climatic dependence of stable carbon and oxygen isotope signals recorded in speleothems from soil water to speleothem calcite abstract understanding the relationship between stable isotope signals recorded in speleothems 13 c and 18 o and the isotopic composition of the carbonate species in the soil water is of great importance for their interpretation in terms of past climate variability here the evolution of the carbon isotope composition of soil water on its way down to the cave during dissolution of limestone is studied for both closed and open closed conditions with respect to co 2 the water entering the cave flows as a thin film towards the drip site co 2 degasses from this film within approx 10 s by molecular diffusion subsequently chemical and isotopic equilibrium is established on a time scale of several 10 100 s the 13 c value of the drip water is mainly determined by the isotopic composition of soil co 2 the evolution of the 18 o value of the carbonate species is determined by the long exchange time t ex between oxygen in carbonate and water of several 10 000 s even if the oxygen of the co 2 in soil water is in isotopic equilibrium with that of the water dissolution of limestone delivers oxygen with a different isotopic composition changing the 18 o value of the carbonate species consequently the 18 o value of the rainwater will only be reflected in the drip water if it has stayed in the rock for a sufficiently long time after the water has entered the cave the carbon and oxygen isotope composition of the drip water may be altered by co 2 exchange with the cave air exchange times ex co 2 of about 3000 s are derived thus only drip water which drips in less than 3000 s onto the stalagmite surface is suitable to imprint climatic signals into speleothem calcite deposited from it precipitation of calcite proceeds with time constants p of several 100 s different rate constants and equilibrium concentrations for the heavy and light isotopes respectively result in isotope fractionation during calcite precipitation since t ex p exchange with the oxygen in the water can be neglected and the isotopic evolution of carbon and oxygen proceed analogously for drip intervals t d p the isotopic compositions of both carbon and oxygen in the solution evolve linearly in time the calcite precipitated at the apex of the stalagmite reflects the isotopic signal of the drip water for long drip intervals when calcite is deposited from a stagnant water film long drip intervals may have a significant effect on the isotopic composition of the dic in this case the isotopic composition of the calcite deposited at the apex must be determined by averaging over the drip interval such processes must be considered when speleothems are used as proxies of past climate variability

latitudinal structure and extension of the polar atmospheric disturbance the dissipation of solar wind energy in the upper atmosphere generates a disturbance whose morphology depends on local time season and magnetic activity a statistical analysis of esro 4 data reveals that 1 in the afternoon evening sector the disturbance boundary coincides with the region of electric current dissipation along the auroral oval 2 in the midnight early morning sector dynamical effects extend the disturbance zone to lower latitudes and this expansion is strongly dependent on season and magnetic activity and 3 in the late morning sector direct heating effects along the auroral oval are superimposed on the residuals of the early morning disturbance these results are consistent with previous observations and provide new boundary conditions for upper atmospheric models

impacts of convectively coupled kelvin waves on environmental conditions for atlantic tropical cyclogenesis abstracthigh amplitude convectively coupled equatorial atmospheric kelvin waves cckws are explored over the tropical atlantic during the boreal summer 1989 2009 focus is given to the atmospheric environmental conditions that are important for tropical cyclogenesis cckws are characterized by deep westerly vertical wind shear to the east of its convectively active phase and easterly vertical wind shear to the west of it this dynamical signature increases vertical wind shear over the western tropical atlantic ahead of the convectively active phase and reduces vertical wind shear after its passage the opposite is true over the eastern tropical atlantic where the climatological vertical wind shear is easterly positive total column water vapor tcwv anomalies progress eastward with the convectively active phase of the cckw whereas negative tcwv anomalies progress eastward with the convectively suppressed phase during the passage of the convectively active phase of the cckw a zonally oriented strip o

dependence of thermospheric zonal winds on solar flux geomagnetic activity and hemisphere as measured by champ the thermospheric zonal winds measured by the champ satellite are used to statistically determine climatology under quiet and active geomagnetic conditions by collectively analyzing the bin averaged wind trend with f10 7 and the solar induced difference in wind structures the solar flux dependence of global thermosphere zonal wind is determined the increase of solar flux enhances the eastward winds at low latitudes from 18 06 mlt the increased ion drag reduces the night time eastward wind in the subauroral latitudes and the daytime westward winds from 06 08 mlt at all latitudes decrease with increasing solar flux zonal winds show coupled seasonal extreme ultraviolet euv dependency the equatorial zonal winds from 18 04 mlt indicate weaker eastward winds during the june solstice at high solar flux levels quiet time eastward winds at subauroral latitudes from 16 20 mlt are further decreased in the winter hemisphere influenced by asymmetries in solar illumination and the magnetic field zonal winds show hemispheric asymmetries quiet daytime winds are additionally influenced by solar illumination effects and the westward winds at the middle and subauroral latitudes are always stronger in the summer the night time eastward winds are higher in the winter hemisphere during the solstices as in the southern hemisphere during equinoxes with the winter summer asymmetry lessened or receding at the solar maxima storm induced subauroral westward disturbance winds are higher in the summer hemisphere and in the northern hemisphere during equinoxes at a high level of solar flux the westward disturbance winds are comparable in the two hemispheres during december solstice geomagnetic disturbance wind observations from champ agree well with the empirical geomagnetic disturbance wind model dwm07 except for stronger subauroral westward jets westward winds during the afternoon may be enhanced in the auroral latitudes before the initial time of a storm main phase

cycles and propagation of deep convection over equatorial africa abstractlong term statistics of organized convection are vital to improved understanding of the hydrologic cycle at various scales satellite observations are used to understand the timing duration and frequency of deep convection in equatorial africa a region with some of the most intense thunderstorms yet little has been published about the propagation characteristics of mesoscale convection in that region diurnal subseasonal and seasonal cycles of cold cloud proxy for convective precipitation are examined on a continental scale organized deep convection consists of coherent structures that are characteristic of systems propagating under a broad range of atmospheric conditions convection is triggered by heating of elevated terrain sea land breezes and lake breezes coherent episodes of convection result from regeneration of convection through multiple diurnal cycles while propagating westward they have an average 17 6 h duration and 673 km span most have zonal phase speeds of 8 16 m s 1 p

altitude variations of the horizontal thermospheric winds during geomagnetic storms 1 it is generally assumed that viscosity smooths out vertical gradients of the horizontal thermospheric winds in the upper thermosphere and thus observations of neutral winds at one height can be used at other altitudes in this region in this paper we present neutral wind simulations of the may 1997 geomagnetic storm using the coupled magnetosphere ionosphere thermosphere cmit model the model results show that during quiet periods the assumption of a shearless vertical profile of the horizontal winds is generally valid in low and middle latitudes although vertical shears do occur in wind profiles in the upper thermosphere in some locations at higher latitudes during disturbed periods large variations in the vertical profiles of the upper thermospheric winds are seen globally in the model simulations a diagnostic analysis of the forcing processes in the neutral momentum equations shows that 1 during quiet time there are shearing forces most noticeably the pressure gradient and ion drag in the upper thermosphere that result in a net momentum forcing that changes with height this induces altitude variations in the wind profiles at high latitudes and sometime even at middle latitudes 2 during storm time momentum advection which is relatively weak during the quiet time becomes a dominant force globally pressure gradient forces are also significantly enhanced ion drag on the other hand can be enhanced or suppressed depending on the location of positive or negative effects all these forces exhibit significant altitude variations that lead to a net force that is greatly enhanced and has large vertical shears this produces globally enhanced neutral winds that vary with height 3 viscosity is less important than other forcing processes during both the quiet and storm periods and thus cannot prevent shears from occurring in the vertical profiles of the horizontal winds viscosity has an insignificant effect on vertical shears that change with height linearly it however does restrict vertical shears that vary nonlinearly with height the effectiveness of the viscosity in restricting such shears depends on its magnitude in our simulations viscosity is weaker than other forcing processes and thus is a relatively slow process so it will take a few hours for viscosity to reduce such shears

synoptic wave perturbations and convective systems over equatorial africa abstract spectral analysis of the outgoing longwave radiation olr time series over equatorial africa reveals large oscillations of the convection with periods of between 3 and 6 days in march and april when the intertropical convergence zone itcz migrates northward and crosses equatorial africa this periodic behavior is most pronounced with a marked peak at 5 6 days robust horizontal and vertical patterns consistent with a convectively coupled kelvin wave can be extracted by a simple composite technique based only on the phase of the convective oscillations over equatorial africa the composite reveals differences between continental and adjacent oceanic regions over the continent the stronger oscillation of the convection is associated with larger temperature and moisture anomalies near the surface suggesting an influence of diabatic processes on the amplitude of the perturbations some convective events over equatorial africa are triggered by waves propagating eastward over the equatorial a

convection activity over the guinean coast and central africa during northern spring from synoptic to intra seasonal timescales this study proposes an overview of the main synoptic medium range and intraseasonal modes of convection and precipitation in northern spring march june 1979 2010 over west and central africa and to understand their atmospheric dynamics it is based on daily national oceanic and atmospheric administration outgoing longwave radiation and cloud archive user service tb convection data daily trmm and global precipitation climatology project rainfall products and daily era interim reanalysis atmospheric fields it is first shown that mesoscale convective systems can be modulated in terms of occurrences number and intensity at such time scales based on empirical orthogonal function analyses on the 2 90 day filtered data it is shown that the main mode of convective and rainfall variability is located along the guinean coast with a moderate to weak extension over central africa corresponding regressed deseasonalised atmospheric fields highlight an eastward propagation of patterns consistent with convectively coupled equatorial kelvin wave dynamics then a singular spectrum analysis combined with a hierarchical ascendant classification enable to define objectively the main spectral bands of variability within the 2 90 day band and highlight three main bands 2 8 8 22 and 20 90 day within these three bands space time spectral decomposition is used to identify the relative impacts of convectively coupled equatorial kelvin rossby and inertia gravity waves as well as madden julian oscillation mjo signal it confirms that eastward propagating signals convectively coupled equatorial kelvin wave and mjo are highly dominant in these convection and precipitation variability modes over the guinean coast during northern spring so while rain producing individual systems are moving westward their activity are highly modulated by sub regional and regional scales envelops moving to the east this is a burning issue for operational forecasting centers to be able to monitor and predict such eastward propagating envelops of convective activity

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

an analysis of the environmental moisture impacts of western north pacific tropical cyclones abstractthe present study examines the environmental moisture anomalies present during western north pacific tropical cyclone tc passage using storm relative composites composited precipitable water anomalies reveal asymmetric anomalies with dry anomalies to the northwest and southwest of the tc and moist anomalies to the east of the tc precipitable water anomalies filtered in space and time suggest that the moisture anomalies in the northwest southwest and east regions nwr swr and er respectively are partially due to the tc while the anomalies in the swr are also forced by a convectively suppressed madden julian oscillation mjo and equatorial rossby wave erw composited vertically integrated moisture budgets and backward parcel trajectories reveal that the moisture anomalies in the nwr swr and er are primarily due to the convergence of climatological mean moisture by the anomalous meridional wind this convergence is induced by the secondary circulation of the tc in the nwr and er and b

meridional neutral winds in the thermosphere at arecibo simultaneous incoherent scatter and airglow observations simultaneous measurements of ion and neutral wind velocities have been obtained at arecibo puerto rico on several nights in both the summer and winter seasons the diffusion velocity of o calculated in an analysis by using the accepted value for the ambipolar diffusion coefficient and the msis model atmosphere is found to be in fairly close agreement with the observations incoherent scatter radar data have also been used to derive height profiles of the meridional neutral wind velocity in the spring and summer months the meridional wind is strongest near 2100 ast with a southward velocity ranging from 50 100 m s 1 at about 0100 ast the midnight descent of the f layer occurs in association with a slackening or sometimes a reversal of the meridional wind in general the meridional wind is fairly constant with altitude however prior to midnight in the spring and summer months contours of constant velocity are often observed to slope downward with increasing time some degree of vertical wind shear is often observed between 0200 and 0500 ast as well in the winter months meridional wind velocities are lower and the nocturnal variation of the wind field is less pronounced than it is at other seasons

atlantic seasonal hurricane frequency part i el nino and 30 mb quasi biennial oscillation influences abstract this is the first of two papers on atlantic seasonal hurricane frequency in this paper seasonal hurricane frequency as related to e1 nino events during 1900 82 and to the equatorial quasi biennial oscillation qbo of stratospheric zonal wind from 1950 to 1982 is discussed it is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes hurricane days and tropical storms and moderate or strong 15 cases el nin off the south american west coast a similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and or are becoming more easterly with time during the hurricane season this association of atlantic hurricane activity with el nino can also be made with the southern oscillation index by contrast seasonal hurricane frequency is slightly above normal in non el nino years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and or are bec

the evolution of 13 c and 18 o isotope composition of dic in a calcite depositing film of water with isotope exchange between the dic and a co 2 containing atmosphere and simultaneous evaporation of the water implication to climate proxies from stalagmites a theoretical model abstract the most widely applied climate proxies in speleothems are the isotope compositions of carbon and oxygen expressed by 13c and 18o values however mechanisms which are not related to climate changes overlay the climate signal one is the temporal increase of both 13c and 18o values by kinetic processes during precipitation of calcite isotope exchange between dic in the water and the co2 in the surrounding cave atmosphere can also change isotope composition here we present a theoretical model of the temporal isotope evolution of dic in a thin water layer during precipitation of calcite and simultaneous isotope exchange with the cave atmosphere and simultaneous evaporation of water the exchange of oxygen isotopes in the dic with those in the water is also considered for drip times for tdrip dic t drip e c eq c 0 e t drip eq atm 0 t drip in atm eq water 0 e w t drip t ev t drip water the first term on the right hand side is the contribution from precipitation of calcite the second stems from isotope exchange with the co2 of the cave atmosphere and the third results from isotope exchange between oxygen in the dic and the oxygen in the water e are kinetic parameters is the time scale of precipitation eq atm 0 and eq water 0 are the differences between the corresponding initial value 0 and the value eq atm water if dic were in isotope equilibrium with the atmosphere or in the case of oxygen with the water respectively in atm and water are the time scales of approach to isotope equilibrium by the exchange reactions ceq is the concentration of dic in chemical equilibrium with the co2 in the cave atmosphere and c0 is the initial concentration when the water drips to the stalagmite tev is the time needed for complete evaporation of the water layer ew is the fractionation between water vapor and fluid water for times tdrip 0 2 we find a further increase of dic tdrip until a maximum is passed and a final value is reached if eq atm 0 and eq water 0 are both zero exchange has no influence on the isotope composition for drip times tdrip eq atm 0 is about zero in summer time when most of the co2 comes from the vadose zone ground air and about 12 in winter time in well ventilated caves when most of the co2 stems from earth s atmosphere outside the cave therefore 13c may be affected by isotope exchange for the 18o equilibrium between the dic and the oxygen in the water as well as the oxygen in the co2 of the atmosphere is likely in summer time in winter time co2 from the atmosphere outside the cave with of about 6 vpdb may imprint small signals

interannual to multidecadal variability of vertical shear and tropical cyclone activity abstractspatiotemporal patterns of tropics wide vertical shear variability are extracted after separating a 58 yr data record into high frequency hf periods of 1 5 8 yr and low frequency lf periods greater than 8 yr components the hf vertical shear variability is dominated by circulation anomalies associated with the el nino southern oscillation enso the lf variability is primarily contained in two multidecadal patterns and a near decadal pattern the multidecadal modes are strongest within the tropical atlantic and are correlated with sahel precipitation and interhemispheric sea surface temperature sst anomalies the results suggest that the multidecadal variability of vertical shear over the atlantic is linked to atmospheric circulation anomalies forced by the variability in sahel precipitation the decadal mode is strongest within the central pacific and is correlated with pacific decadal oscillation pdo like sst anomalies the circulation associated with this anomalous shear pattern appea

convectively coupled kelvin waves and tropical cyclogenesis in a semi lagrangian framework abstractthis study examines how convectively coupled kelvin waves interact with the semi lagrangian circulation of easterly waves to modulate tropical cyclogenesis recent studies have shown that fewer tropical cyclones form in the three days before passage of the kelvin wave s peak convection and more develop in the three days thereafter separately other studies have identified the recirculation of moisture and vorticity within easterly waves using a semi lagrangian frame of reference that framework is achieved by subtracting the easterly wave phase speed from the earth relative winds this study combines these recent findings by testing whether the equatorial westerlies from kelvin waves can help close the semi lagrangian circulation past studies have shown that kelvin waves tilt westward with height in the troposphere such that equatorial westerlies build upward from the surface in the days following the convective peak this study shows that the easterly wave s semi lagrangian closed circulation gr

easterly wave regimes and associated convection over west africa and tropical atlantic results from the ncep ncar and ecmwf reanalyses ncep ncar and ecmwf daily reanalyses are used to investigate the synoptic variability of easterly waves over west africa and tropical atlantic at 700 hpa in northern summer between 1979 1995 1979 1993 for ecmwf spectral analysis of the meridional wind component at 700 hpa highlighted two main periodicity bands between 3 and 5 days and 6 and 9 days the 3 5 day easterly wave regime has already been widely investigated but only on shorter datasets these waves grow both north and south of the african easterly jet aej the two main tracks noted over west africa at 5 n and 15 n converge over the atlantic on latitude 17 5 n these waves are more active in august september than in june july their average wavelength phase speed varies from about 3000 km 8 m s 1 north of the jet to 5000 km 12 m s 1 south of the jet rainfall convection and monsoon flux are significantly modulated by these waves convection in the inter tropical convergence zone itcz being enhanced in the trough and ahead of it with a wide meridional extension compared to the 3 5 day waves the 6 9 day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics the only main track is located north of the aej along 17 5 n both over west africa and the atlantic the mean wavelength is higher about 5000 km long and the average phase speed is about 7 m s 1 then the wind field perturbation is mostly evident at the aej latitude and north of it the perturbation structure is similar to that of 3 5 days in the north except that the more developed circulation centers moving more to the north lead to a large modulation of the jet zonal wind component south of the aej the wind field perturbation is weaker and quite different the zonal wind core of the jet appears to be an almost symmetric axis in the 6 9 day wind field pattern a clockwise circulation north of the aej being associated with a counter clockwise circulation south of the jet and vice versa these 6 9 day easterly waves also affect significantly rainfall convection and monsoon flux but in a different way inducing large zonal convective bands in the itcz mostly in the trough and behind it as opposed to the 3 5 day wave regime these rainfall anomalies are associated with anomalies of opposite sign over the guinea coast and the sahelian regions over the continent these waves are more active in june july and in august september over the ocean gate phase i gave an example of such an active 6 9 day wave pattern considered as a sequence of weak easterly wave activity this phase was also a sequence of high 6 9 day easterly wave activity we suggest that the 6 9 day regime results from an interaction between the 3 5 day easterly wave regime maintained by the barotropic baroclinic instability of the aej and the development of strong anticyclonic circulations north of the jet over west africa and both north and south of the jet over the atlantic significantly affecting the jet zonal wind component the permanent subtropical anticyclones azores libya st helena could help initiation and maintenance of such regime over west africa and tropical atlantic based on an a priori period band criterion our synoptic classification has enabled us to point out two statistical and meteorological easterly wave regimes over west africa and tropical atlantic ncep ncar and ecmwf reanalyses are in good agreement the main difference being a more developed easterly wave activity in the ncep ncar reanalyses especially for the 3 5 day regime over the atlantic

case study of a developing african easterly wave during namma an energetic point of view abstract the west african perturbation that subsequently evolved into hurricane helene 2006 during nasa s african monsoon multidisciplinary analysis namma 15 august 14 september 2006 and amma s third special observing period sop 3 15 29 september 2006 has been simulated with the nonhydrostatic meso nh model using parameterized convection the simulated disturbance evolved over west africa and the adjacent eastern tropical atlantic through interactions between different processes at the convective scale mesoscale and synoptic scale the aim of this paper is to quantify the energetics of the simulated disturbance a set of energy equations is first developed in the hydrostatic case to solve the limitations of lorenz s analysis when applied to a finite domain it is shown that this approach is also valid in the compressible and in the anelastic case in order to apply it to the meso nh results application to the simulated pre helene disturbance allows one to determine the most important terms in

an empirical model of the earth s horizontal wind fields hwm07 1 the new horizontal wind model hwm07 provides a statistical representation of the horizontal wind fields of the earth s atmosphere from the ground to the exosphere 0 500 km it represents over 50 years of satellite rocket and ground based wind measurements via a compact fortran 90 subroutine the computer model is a function of geographic location altitude day of the year solar local time and geomagnetic activity it includes representations of the zonal mean circulation stationary planetary waves migrating tides and the seasonal modulation thereof hwm07 is composed of two components a quiet time component for the background state described in this paper and a geomagnetic storm time component dwm07 described in a companion paper

sources of tropical subseasonal skill in the cfsv2 abstractthis study applies fourier filtering to a combination of rainfall estimates from trmm and forecasts from the cfsv2 the combined data are filtered for low frequency lf 120 days variabil

the role of convectively coupled atmospheric kelvin waves on african easterly wave activity abstractthe role of convectively coupled atmospheric kelvin waves cckws on african easterly wave aew activity is explored over tropical africa during boreal summer examination of the pre alberto aew in 2000 highlights the observation that the convective trigger for the initiation of the aew was generated by a strong cckw and that the subsequent intensification of the aew at the west african coast was associated with a second cckw composite analysis shows that generally aew activity increases during and after the passage of the convectively active phase of strong cckws the increase in aew activity is consistent with convective triggering at the leading edge of the convective phase of the cckw this convective triggering occurs in a region where the background low level easterly vertical wind shear is increased by the cckw as the aew propagates westward through the convectively active phase of the cckw it can develop in an environment favorable for convection it is also shown that this phase of

squall lines and convectively coupled gravity waves in the tropics why do most cloud systems propagate westward abstractthe coupling between tropical convection and zonally propagating gravity waves is assessed through fourier analysis of high resolution 3 hourly 0 5 satellite rainfall data results show the familiar enhancement in power along the dispersion curves of equatorially trapped inertia gravity waves with implied equivalent depths in the range 15 40 m i e pure gravity wave speeds in the range 12 20 m s 1 here such wave signals are seen to extend all the way down to zonal wavelengths of around 500 km and periods of around 8 h suggesting that convection wave coupling may be important even in the context of mesoscale squall lines this idea is supported by an objective wave tracking algorithm which shows that many previously studied squall lines in addition to 2 day waves can be classified as convectively coupled inertia gravity waves with the dispersion properties of shallow water gravity waves most of these disturbances propagate westward at speeds faster than the background flow to under

observations of a convectively coupled kelvin wave in the eastern pacific itcz abstract a case study of a convectively coupled kelvin wave in the eastern pacific intertropical convergence zone itcz is presented as observed during the 1997 pan american climate studies pacs tropical eastern pacific process study tepps the large scale convective envelope associated with this disturbance with a zonal scale of approximately 1000 2000 km propagates eastward at 15 m s 1 along the mean convective axis of the itcz this envelope consists of many smaller scale westward moving convective elements with zonal scales on the order of 100 500 km as the convectively coupled kelvin wave disturbance propagates eastward it exerts a strong control on local convection radar and vertical profiler data collected aboard the noaa r v ronald h brown during the wave passage show that convection deepens rapidly as the kelvin wave approaches from the west progressing from isolated shallow cumuli to organized deep convective features within just 12 h initially rainfall in the vicinity of the s

on the generation decay of the storm enhanced density plumes role of the convection flow and field aligned ion flow storm enhanced density sed plumes are prominent ionospheric electron density increases at the dayside middle and high latitudes the generation and decay mechanisms of the plumes are still not clear we present observations of sed plumes during six storms between 2010 and 2013 and comprehensively analyze the associated ionospheric parameters within the plumes including vertical ion flow field aligned ion flow and flux plasma temperature and field aligned currents obtained from multiple instruments including gps total electron content tec poker flat incoherent scatter radar pfisr super dual auroral radar network and active magnetosphere and planetary electrodynamics response experiment the tec increase within the sed plumes at the pfisr site can be 1 4 5 5 times their quiet time value the plumes are usually associated with northwestward e b flows ranging from a couple of hundred m s 1 to 1 km s 1 upward vertical flows due to the projection of these e b drifts are mainly responsible for lifting the plasma in sunlit regions to higher altitude and thus leading to plume density enhancement the upward vertical flows near the poleward part of the plumes are more persistent while those near the equatorward part are more patchy in addition the plumes can be collocated with either upward or downward field aligned currents facs but are usually observed equatorward of the peak of the region 1 upward fac suggesting that the northwestward flows collocated with plumes can be either subauroral or auroral flows furthermore during the decay phase of the plume large downward ion flows as large as 200 m s 1 and downward fluxes as large as 1014 m 2 s 1 are often observed within the plumes in our study of six storms enhanced ambipolar diffusion due to an elevated pressure gradient is able to explain two of the four large downward flow flux cases but this mechanism is not sufficient for the other two cases where the flows are of larger magnitude for the latter two cases enhanced poleward thermospheric wind is suggested to be another mechanism for pushing the plasma downward along the field line these downward flows should be an important mechanism for the decay of the sed plumes

tropical cyclogenesis associated with kelvin waves and the madden julian oscillation abstractthe madden julian oscillation mjo influences tropical cyclone formation around the globe convectively coupled kelvin waves are often embedded within the mjo but their role in tropical cyclogenesis remains uncertain this case study identifies the influences of the mjo and a series of kelvin waves on the formation of two tropical cyclones typhoons rammasun and chataan developed in the western north pacific on 28 june 2002 two weeks earlier conditions had been unfavorable for tropical cyclogenesis because of uniform trade easterlies and a lack of organized convection the easterlies gave way to equatorial westerlies as the convective envelope of the madden julian oscillation moved into the region a series of three kelvin waves modulated the development of the westerlies cyclonic potential vorticity pv developed in a strip between the growing equatorial westerlies and the persistent trade easterlies farther poleward rammasun and chataan emerged from the apparent breakdown of this strip the

first palmer and millstone hill midlatitude conjugate observation of thermospheric winds the first midlatitude conjugate thermospheric wind observations in the american sector showed various degrees of conjugacy between palmer 64 s 64 w magnetic latitude mlat 50 s and millstone hill 42 82 n 71 5 w mlat 53 n under three different geomagnetic conditions recovery after a substorm moderately active and quiet the agreement with the national center for atmospheric research s thermosphere ionosphere electrodynamics general circulation model tiegcm simulations also varies with the geomagnetic activity level during substorm recovery the observations at palmer pa and millstone hill mh both showed strong westward zonal winds which the standard tiegcm greatly underestimated inadequate ion convection pattern size and lack of effect from subauroral polarization streams saps may be the cause of the large discrepancy the tiegcm with a saps model produced stronger westward zonal winds near pa but did not change the zonal wind near mh the empirical saps model needs further refinements in general there is better conjugacy with moderate geomagnetic activity levels the tiegcm also agrees better with the observations under geomagnetically quiet conditions the meridional winds appear to be less conjugate the agreement between the observations and model is reasonable optical conjugate observations are severely limited by the seasons and weather conditions in the two hemispheres yet they are necessary to understanding the thermospheric dynamics in the subauroral region and its relationship with geomagnetic activity levels the comparisons with tiegcm are necessary for future model improvements

a climatological study of transient mean flow interactions over west africa a statistical study is made of the relationship between intraseasonal variations in mid tropospheric flow over west africa and transient eddy activity during the june september monsoon season in order to investigate the interaction between the african easterly jet aej african easterly waves aews and convection ncep2 reanalyses are used together with outgoing long wave radiation olr data from june september 1979 2007 intraseasonal variability in the 600 hpa zonal wind is isolated using a 10 120 day filter the leading empirical orthogonal function eof describes north south displacements of the jet axis episodes of aew activity over the continent are evaluated in terms of the perturbation kinetic energy pke of the less than six day high pass filtered wind at 700 and 850 hpa pke and olr are also filtered for the intraseasonal signal lag covariance analyses reveal a two way interaction between the aej and synoptic scale transients prior to episodes of enhanced transient activity the aej is strengthened in the jet entrance region during and following these episodes the aej is strengthened on the northern flank of the jet exit region e vector analysis shows that this displacement of the aej is consistent with forcing by transients that have an aew like structure analysis of olr shows that periods of enhanced transient activity over west africa are associated with enhanced convection over the region at intraseasonal time scales and are correlated with prior episodes of enhanced convection to the east in the convective trigger region identified by thorncroft et al copyright 2009 royal meteorological society

three dimensional structure and dynamics of african easterly waves part i observations the mean structure of african easterly waves aews over west africa and the adjacent atlantic is isolated by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered satellite derived outgoing longwave radiation these results are compared with previous studies and an idealized modeling study in a companion paper which provides evidence that the waves bear a close structural resemblance to the fastest growing linear normal mode of the summertime basic state flow over africa there is a significant evolution in the three dimensional structure of aews as they propagate along 10 n across west africa at this latitude convection occurs in northerly flow to the east of the greenwich meridian then shifts into the wave trough and finally into southerly flow as the waves propagate offshore into the atlantic itcz in contrast to the north of the african easterly jet along 15 n convection remains in southerly flow throughout the waves trajectory along 10 n over west africa the location of convection is consistent with the adiabatic dynamical forcing implied by the advection of perturbation vorticity by the mean thermal wind in the zonal direction as in the companion paper offshore and along 15 n the relationship between the convection and dynamics is more complex and not as easily explained in terms of dynamical forcing alone

multidecadal variability in north atlantic tropical cyclone activity abstract recent increases in atlantic basin tropical cyclone activity since 1995 and the associated destructive u s landfall events in 2004 and 2005 have generated considerable interest into why there has been such a sharp upturn natural variability human induced global warming or a combination of both factors have been suggested several previous studies have discussed observed multidecadal variability in the north atlantic over 25 40 yr time scales this study using data from 1878 to the present creates a metric based on far north atlantic sea surface temperature anomalies and basinwide north atlantic sea level pressure anomalies that shows remarkable agreement with observed multidecadal variability in both atlantic basin tropical cyclone activity and in u s landfall frequency

origin of convectively coupled kelvin waves over south america convectively coupled kelvin waves over the south american continent are examined through the use of temporal and spatial filtering of reanalysis satellite and gridded rainfall data they are most prominent from november to april the season analyzed herein the following two types of events are isolated those that result from preexisting kelvin waves over the eastern pacific ocean propagating into the continent and those that apparently originate over amazonia forced by disturbances propagating equatorward from central and southern south america the events with precursors in the pacific are mainly upper level disturbances with almost no signal at the surface those events with precursors over south america on the other hand originate as upper level synoptic wave trains that pass over the continent and resemble the cold surges documented by garreaud and wallace as the wave train propagates over the andes it induces a southerly low level wind that advects cold air to the north precipitation associated with a cold front reaches the equator a few days later and subsequently propagates eastward with the characteristics of a kelvin wave the structures of those waves originating over the pacific are quite similar to those originating over south america as they propagate to eastern south america and into the atlantic south america kelvin waves that originate over neither the pacific nor the midlatitudes of south america can also be identified in a composite sense these form over the eastern slope of the andes mountains close to the equator there are also cases of cold surges that reach the equator yet do not form kelvin waves the interannual variability of the pacific originating events is related to sea surface temperatures in the central eastern pacific ocean when equatorial oceanic conditions are warm there tends to be an increase in the number of disturbances that reach south america from the pacific

a statistical analysis of sporadic e layer occurrence in the midlatitude china region a statistical analysis of sporadic e layer recorded from september 2011 to september 2015 at four chinese ionospheric sounding stations of mohe 122 37 e 53 50 n beijing 116 25 e 40 25 n wuhan 114 61 e 30 53 n and hainan 109 13 e 19 52 n are presented to investigate the characteristics of sporadic e layer at the middle latitudes over china the occurrence of the sporadic e layer in mid latitude china region shows strong dependence on local time and season consistent with previous studies the occurrence of the mid latitude sporadic e layer is prominent at local daytime in summer season the results also reveal that the post sunset sporadic e layer is statistically pronounced in mid latitude china region possibly related to the nighttime mid latitude e region irregularities the mid latitude sporadic e layer is modulated by atmospheric tidal waves and planetary waves at different latitudes the occurrence of the mid latitude sporadic e layer also tends to increase with the level of geomagnetic activity on basis of both the statistical analysis and case study

analysis of convectively coupled kelvin waves in the indian ocean mjo abstract the active convective phase of the madden julian oscillation hereafter active mjo comprises enhanced moist deep convection on its own temporal and spatial scales as well as increased variance in convection associated with higher frequency modes synoptic scale cloud superclusters apparently associated with convectively coupled kelvin waves occur within the active convective envelopes of most mjo events these convectively coupled kelvin waves also occur during the suppressed convective phase of the mjo hereafter suppressed mjo this observational study presents an analysis of outgoing longwave radiation and reanalysis data to determine how these waves behave differently as they propagate through the active and suppressed mjo time indices of the mjo and kelvin waves are derived for over the equatorial indian ocean dates of local extrema in these indices are used to composite data to discern how the waves and associated circulations behave on average then further composites are made based o

a climatology of waves in the equatorial region abstract propagating anomalies of moisture and moist deep convection in the tropics are organized into a variety of large scale modes these include but are not limited to the so called intraseasonal oscillations convectively coupled waves similar to those predicted by shallow water theory on the equatorial beta plane and tropical depression type disturbances along with the annual and diurnal cycles these modes act and interact to control much of the variance of tropical convection analyses of 10 yr of outgoing longwave radiation olr and precipitable water pw data are carried out to develop comparative climatologies of these wavelike modes the analysis relaxes the commonly used cross equatorial symmetry constraints which allows study of the portions of the wavelike processes that are asymmetric across the equator mean background states are found for olr and for pw as functions of day of the year examination of anomalies together with the background reveals much about how the waves are affec

convectively coupled kelvin waves over tropical africa during the boreal summer structure and variability the structure and variability of convectively coupled kelvin waves during the boreal summer are explored using satellite observed brightness temperature data and ecmwf reanalyses kelvin wave activity is most prominent between the central and eastern pacific across africa and the indian ocean composite analysis shows that over sub saharan africa kelvin wave convection is peaked north of the equator while the dynamical fields tend to be symmetric with respect to the equator convectively coupled kelvin waves propagate faster over the pacific and western atlantic 24 m s 1 and slow down over tropical africa 14 m s 1 consistent with stronger coupling between the dynamics and convection over tropical africa the kelvin waves observed over africa generally propagate into the region from anywhere between the eastern pacific and the atlantic and decay over the eastern indian ocean basin results show marked interannual variability of kelvin wave activity over africa anomalously high kelvin wave variance tends to occur during dry years while low variance occurs during wet years african kelvin wave activity is positively correlated with sst anomalies in the equatorial east pacific the same warm sst anomalies that are favorable for enhanced kelvin wave activity suppress the mean rainfall over tropical africa via a more slowly varying teleconnection and associated subsidence a brief analysis of an intense kelvin wave in august 1987 a dry year shows a clear impact of the wave on convective development and daily rainfall over tropical africa this kelvin wave was also associated with a series of easterly wave initiations over tropical africa

average daytime f region disturbance neutral winds measured by uars initial results thermospheric neutral winds play important roles on the dynamics of the upper atmosphere we use extensive f region zonal and meridional wind data measured by the wind imaging interferometer windii instrument on board the upper atmosphere research satellite uars to study the mid and low latitude daytime average perturbation winds during magnetically disturbed periods we have determined the perturbation winds by subtracting the quiet time wind values along the satellite orbits our data indicate large changes in the latitudinal profiles of both the zonal and meridional disturbance winds from morning to afternoon hours the early morning zonal disturbance winds are eastward near the equator and at upper mid latitudes above 50o and westward at lower mid latitudes the mid morning and afternoon zonal disturbance wind patterns show very small amplitudes at low latitudes and increasing westward winds at mid latitudes these latitudinal profiles are in excellent agreement with the patterns derived from zonal wind measurements on board the de 2 satellite the meridional daytime perturbation winds are equatorward and have magnitudes increasing linearly with latitude with largest values in the early morning sector the

an analysis of west african dynamics using a linearized gcm abstract this study utilizes a linear primitive equation spherical model to study the development and propagation of easterly wave disturbances over west africa perturbations are started from an initial disturbance consisting of a barotropic vortex and the governing equations are integrated forward in time the perturbations are introduced into basic states corresponding to the observed dynamical and thermodynamical characteristics of two wet years in the sahel and two dry years the model simulations show consistent contrasts in wave activity between the wet and dry years the waves are markedly stronger in the wet years and show a barotropic structure throughout the troposphere the waves tend to extend throughout the troposphere to the level of the tropical easterly jet tej in the wet years but not in the dry years the upper tropospheric shear which is stronger in wet years appears to be a key factor in wave development this shear is dependent on the intensity of the tej suggesting that the t

tropical storm development from african easterly waves in the eastern atlantic a comparison of two successive waves using a regional model as part of nasa amma 2006 abstract two successive african easterly waves aews from august 2006 are analyzed utilizing observational data the european centre for medium range weather forecasts reanalysis and output from the national center for atmospheric research national oceanic and atmospheric administration weather research and forecasting model wrf to understand why the first wave does not develop over the eastern atlantic while the second wave does the first aew eventually forms hurricane ernesto over the caribbean sea but genesis does not occur over the eastern atlantic the second wave although weaker than the first over land leaves the west african coast and quickly intensifies into tropical storm debby west of the cape verde islands this study shows that the environmental conditions associated with the first aew s passage inhibited development these conditions include strong low and midtropospheric vertical wind shear owing to a stronger than normal african easterly jet lower than normal relative humidity a

comment on maximilian hansen denis scholz bernd r schone christoph spotl simulating speleothem growth in the laboratory determination of the stable isotope fractionation δ13c and δ18o between h2o dic and caco3 chemical geology 509 2019 20 44 abstract in this comment it is shown that analysis of the fractionation constants of the dic describing the enrichment of 13c and 18o along the flow path of a thin water layer flowing down an inclined marble plate precipitating calcite in analogy to precipitation to speleothems enables one to decide whether the rayleigh distillation model or the kinetic model is valid appropriate analysis of etot values for carbon and oxygen as reported by hansen et al 2019 reveals the validity of the kinetic model and allows determining the constants ekin and this is in contrast to findings of hansen and coauthors and gives a deeper understanding of the meaning of kinetic fractionation during precipitation of calcite

the earth s thermospheric superrotation from dynamics explorer 2 neutral thermospheric zonal winds measured from the wind and temperature experiment on dynamics explorer 2 have been analyzed to provide a measure of the superrotation of the neutral thermosphere the data were averaged in local time in 10 degree bands from the equator to 40 degrees latitude the results show an average wind velocity on the order of 18 m s to the east at the equator and a westward wind of the same magnitude at mid latitudes within the range of altitudes of the data base 200 to 700 km no evidence of any significant altitude dependence was found averaging our data over the latitude bands studied indicates a net corotation of the thermosphere this result is not in agreement with the superrotation value reported by king hele and walker on the basis of satellite drag analysis

observations and simulations of quasiperiodic ionospheric oscillations and large scale traveling ionospheric disturbances during the december 2006 geomagnetic storm 1 a numerical simulation was performed to investigate quasiperiodic ionospheric oscillations that were observed with periods of 4 5 h by the ionosonde network okinawa yamagawa kokubunji and wakkanai in japan during the 15 december 2006 magnetic storm this simulation used the coupled magnetosphere ionosphere thermosphere cmit 2 0 model the cmit model reproduced the main characteristics of the observed ionospheric oscillations although it remains a challenging task to simulate the observations in a quantitative sense term analysis of the ion continuity equation demonstrated that the ionospheric oscillations in this event were mainly induced by the disturbed neutral winds which were associated with the large scale thermospheric circulation and traveling atmospheric disturbances tads during the storm the tads simulated from the model were then compared with those observed by the gps earth observation network geonet in japan to validate the simulation results a prominent northward propagating large scale traveling ionospheric disturbance lstid during daytime seen by the geonet total electron content tec data was captured by the cmit model two southward lstids observed by geonet gps network were also reproduced by the cmit model however the model gave faster phase speeds for the southward propagating lstid occurred during 0620 0800 ut and the northward propagating lstid furthermore the model missed the lstid seen in the tec perturbation data during 0140 0220 ut finally both observations and simulations showed a strong hemispheric asymmetry for the tad propagation that occurred during 0000 0400 ut which may be associated with the hemispheric asymmetry of the change of joule heating at high latitude

the madden julian oscillation s influence on african easterly waves and downstream tropical cyclogenesis abstractthe influence of the madden julian oscillation mjo over tropical africa and atlantic is explored during the northern hemisphere summer months the mjo is assessed by using real time multivariate mjo rmm indices these indices divide the active convective signal of the mjo into 8 phases convection associated with the mjo is enhanced over tropical africa during rmm phases 8 1 and 2 convection becomes suppressed over tropical africa during the subsequent rmm phases phases 3 7 african convective signals are associated with westward propagating equatorial rossby waves the mjo modulates african easterly wave aew activity aew activity is locally enhanced during rmm phases 1 3 and suppressed during rmm phases 6 8 enhanced aew activity occurs during periods of enhanced convection over tropical africa consistent with stronger or more frequent triggering of aews as well as more growth associated with latent heat release enhanced aew activity occurs during the low level westerly wind phase of

altitude dependence of middle and low latitude daytime thermospheric disturbance winds measured by windii 1 thermospheric neutral winds exhibit strong altitudinal and latitudinal variation during geomagnetically quiet and active times we use daytime middle and low latitude neutral winds measured by the wind imaging interferometer windii instrument on board the upper atmosphere research satellite uars over the 90 275 km height range to study the altitude and season dependent climatology of disturbance winds i e with quiet time patterns removed in magnetic coordinates the daytime perturbations winds are generally equatorward and westward and decrease toward the magnetic equator both the zonal and meridional components decrease sharply below 120 km and are essentially insignificant below 100 km the seasonal dependence of the disturbance winds is strongest in the early morning sector the zonal disturbance winds are predominantly westward with largest magnitudes near 150 km at late afternoon upper midlatitudes magnetic latitudes 50 60 and near 120 km in the early morning winter between 25 and 45 at upper midlatitudes in the early morning sector the zonal perturbation winds are eastward above 120 km in the summer hemisphere and between 120 and 180 km in the winter hemisphere eastward perturbations are also observed near the magnetic equator with largest values near noon at 250 km the meridional perturbation winds are mostly equatorward and nearly height independent above 150 km with the largest magnitudes occurring in the early morning winter hemisphere in the late afternoon sector the upper midlatitude meridional disturbance winds are poleward and there is a small winter to summer flow at lower latitudes in general the storm time dependence of the disturbance winds is quite complex the perturbation winds begin to develop after 0 9 hours and tend to saturate 12 24 hours after storm onset the development does not change much with altitude and the seasonal dependence is generally important only at storm times greater than 6 12 hours

the west african monsoon dynamics part iii the quasi biweekly zonal dipole abstract this paper presents an investigation of the mechanisms giving rise to the main intraseasonal mode of convection in the african monsoon during northern summer here identified as the quasi biweekly zonal dipole qbzd the qbzd is primarily characterized by a quasi stationary zonal dipole of convection whose dimension is larger than the west african monsoon domain with its two poles centered along the guinean coast and between 30 and 60 w in the equatorial atlantic the qbzd dynamical processes within the atlantic africa domain are examined in some detail the qbzd has a dipole pattern associated with a walker type circulation in the near equatorial zonal plane it is controlled both by equatorial atmospheric dynamics through a kelvin wave like disturbance propagating eastward between its two poles and by land surface processes over africa inducing combined fluctuations in surface temperatures surface pressure and low level zonal winds off the coast of west africa when convection is at a min

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

modulation of the convectively coupled kelvin waves over south america and the tropical atlantic ocean in association with the madden julian oscillation abstractin this study evidence of the strong modulation of the convectively coupled kelvin wave cckw activity by the madden julian oscillation mjo is presented with a particular focus over the south america and tropical atlantic region the mjo impacts on cckws over this region as noted in anomalous fields of rainfall as well as vertical profiles of wind moisture and temperature are primarily through the modulation of kelvin wave amplitude with secondary effects on vertical structure and little impact on wavenumber cckw activity is enhanced during mjo phases 8 1 and 2 and damped during mjo phases 4 5 and 6 further analyses reveal that the strong modulation of the mjo on the cckw activity could be largely through two factors namely the vertical zonal wind shear and the lower to middle tropospheric specific humidity the cckw activity tends to be enhanced during mjo phases when the easterly vertical wind shear and positive low to midtroposphere moisture anomalies are present and vice ve

extratropical forcing of convectively coupled kelvin waves during austral winter abstract observations are presented that link extratropical rossby wave disturbances excited in the southern hemisphere subtropical jet to the initiation of convectively coupled kelvin waves in the pacific intertropical convergence zone itcz during austral winter a baroclinic zonal wavenumber 6 eastward propagating rossby wave train in the subtropical jet turns northeastward in the vicinity of australia inducing upper tropospheric divergence and vertical motion fields that spread equatorward and induce cloudiness anomalies in the tropics lower tropospheric pressure surges excited from the extratropics also induce kelvin wave like geopotential height and temperature anomalies at the surface providing additional lower tropospheric convergence and vertical motion forcing the tropical outgoing longwave radiation olr and circulation fields propagate eastward in tandem with the extratropical rossby wave train at approximately 17 m s 1 kelvin wave activity in the central pacific itcz thus appears to

dynamics of the west african monsoon part iv analysis of 25 90 day variability of convection and the role of the indian monsoon this paper is part of a series of studies addressing the dynamics of the west african summer monsoon at intraseasonal time scales between 10 and 90 days the dominant mode of 25 90 day convective variability in the african monsoon was investigated starting from previous results involving the excitation of dry equatorial kelvin and rossby waves by a negative diabatic heat source located over the warm pool this evolution is consistent with a significant contribution by a convectively coupled equatorial rossby wave and the mjo on the other hand convectively coupled kelvin waves as well as the dry kelvin wave signal have a very weak impact however there is more to the global control of the african summer monsoon than convectively coupled wave dynamics the active break cycle of the indian monsoon controlled by a northward moving dipole of diabatic heating in the indian sector can also influence the african monsoon through atmospheric teleconnections simulations performed with a dry primitive equation model show that this influence may be transferred through the northern indian heat source which excites a rossby cyclonic circulation propagating westward over north africa that is cut off by the northward arrival of the equatorial indian heat source and the associated intrusion of an anticyclonic ridge low level westerly winds and moisture advection within the itcz consequently increase over africa the mean time lag between an active phase over india and over africa is about 15 20 days

an examination of the thermodynamic impacts of western north pacific tropical cyclones on their tropical tropospheric environment abstractthe present study examines the tropospheric thermodynamic anomalies induced by western north pacific tropical cyclone tc passage using storm relative composites negative moist static energy mse anomalies containing embedded westward propagating anomalies generally occur only following larger tcs for two months following tc passage in a region extending from the domain center to 3000 km to its west larger tcs force negative mse anomalies likely because of feedbacks from stronger broader tc induced negative sea surface temperature sst anomalies and the excitation of tc induced rossby waves to the southeast of the tc the negative mse anomalies are composed of lower and midtropospheric negative latent energy anomalies with smaller contributions from boundary layer and upper tropospheric negative sensible heat anomalies the lower and midtropospheric negative mse anomalies are forced by the tc whereas the upper tropospheric negative mse anomalies are forced by the madden julian oscillatio

on the relationship between african easterly waves and the african easterly jet this idealized modeling study investigates how convectively triggered african easterly waves aews are influenced by the intraseasonal variability of the african easterly jet aej a set of 10 day averaged zonally varying basic states is constructed with the ncep 2 reanalysis 1979 2006 a primitive equation model is used to simulate linear aews on each of these basic states using the same idealized convective heating localized over the darfur mountains as an initial trigger it is shown that the transient response depends strongly on the basic state with the same trigger many configurations of the aej fail to produce a wave disturbance while others produce strong easterly wave structures necessary conditions for the development of strong waves can be characterized by a strong jet a strong vertical shear or a strong and extended potential vorticity reversal in strong wave cases the jet is extended to the south and west and the jet core is aligned with the maximum of surface westerlies maximizing the vertical shear the pattern that is optimal for generating easterly waves also closely resembles the dominant mode of variation of the aej revealed by an empirical orthogonal function eof analysis of the set of basic states

analysis of african easterly wave structures and their role in influencing tropical cyclogenesis abstract composite structures of african easterly waves aews that develop into named tropical cyclones in the atlantic are compared and contrasted with nondeveloping aews using the 40 yr ecmwf re analysis era 40 data and satellite brightness temperature between 1979 and 2001 developing aews are characterized by a more distinctive cold core structure two days before reaching the west african coast as they move westward the convective activity increases further in the vicinity of the guinea highlands region at the same time the aew trough increases its vorticity at low levels consistent with a transformation toward a more warm core structure before it reaches the ocean as the aew moves over the ocean convection is maintained in the trough consistent with the observed tropical cyclogenesis the nondeveloping aew has a similar evolution before reaching the coast except that the amplitudes are weaker and there is less convective activity in the guinea highlands region the nondeveloping aew composite

the influence of amazon rainfall on the atlantic itcz through convectively coupled kelvin waves abstract using outgoing longwave radiation olr and tropical rainfall measuring mission trmm daily rain rate data systematic changes in intensity and location of the atlantic intertropical convergence zone itcz were detected along the equator during boreal spring it is found that the changes in convection over the tropical atlantic may be induced by deep convection in equatorial south america lagged regression analyses demonstrate that the anomalies of convection developed over the land propagate eastward across the atlantic and then into africa the eastward propagating disturbances appear to be convectively coupled kelvin waves with a period of 6 7 5 days and a phase speed of around 15 m s 1 these waves modulate the intensity and location of the convection in the tropical atlantic and result in a zonal variation of the atlantic itcz on synoptic time scales the convectively coupled kelvin wave has substantial signals in both the lower and upper troposphere both a reanalysis dataset and the qui

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

a numerical study on the effects of environmental flow on tropical storm genesis abstract the role of the environmental wind in tropical storm genesis is studied using a numerical simulationmodel the model used is an 11 level primitive equation model covering a channel domain of 25 span withopen lateral boundaries at 5 5 and 30 5 n a number of experiments were integrated for 96 h in which theinitial zonal mean flow was specified differently the superposed initial wave disturbances were identicalin all experiments the dynamic coupling between the upper level winds and the low level movement of the disturbance wasfound to be an important factor in explaining the role of the environmental wind in storm genesis anotherimportant factor is the impact of the low level winds on the latent energy supply this supply is affectedby the relative inflow into a disturbance and by the transfer of momentum from aloft into the boundarylayer in a large area surrounding the disturbance according to the model results the storm genesis potential is definitely biased toward easterly verticalshear

observations of seven african easterly waves in the east atlantic during 2006 abstract the african monsoon multidisciplinary analyses amma experiment and its downstream nasa extension namma provide an unprecedented detailed look at the vertical structure of consecutive african easterly waves during august and september 2006 seven easterly waves passed through the namma domain two waves developed into tropical cyclones debby and helene two waves did not develop and three waves were questionable in their role in the development of ernesto florence and gordon ncep global data assimilation system gdas analyses are used to describe the track of both the vorticity maxima and midlevel wave trough associated with each of the seven easterly waves dropsonde data from namma research flights are used to describe the observed wind structure and as a tool to evaluate the accuracy of the gdas to resolve the structure of the wave finally satellite data are used to identify the relationship between convection and the organization of the wind structure results support a necessary d

atlantic tropical cyclogenesis a three way interaction between an african easterly wave diurnally varying convection and a convectively coupled atmospheric kelvin wave abstractthis paper explores a three way interaction between an african easterly wave aew the diurnal cycle of convection over the guinea highlands ghs and a convectively coupled atmospheric equatorial kelvin wave cckw these interactions resulted in the genesis of tropical storm debby over the eastern tropical atlantic during late august 2006 the diurnal cycle of convection downstream of the ghs during the month of august is explored convection associated with the coherent diurnal cycle is observed off the coast of west africa during the morning later convection initiates over and downstream of the ghs during the afternoon these convective features were pronounced during the passage of the pre debby aew the superposition between the convectively active phase of a strong cckw and the pre debby aew occurred shortly after merging with the diurnally varying convection downstream of the ghs the cckw aew interaction preceded tropical cyclogenesis by 18 h the cckw provided a favorable environment

on the madden julian oscillation atlantic hurricane relationship abstract the large scale equatorial circulation known as the madden julian oscillation mjo has been shown to impact tropical cyclone activity in several basins around the globe in this paper the author utilizes an mjo index created by wheeler and hendon to examine its impacts on tropical genesis and intensification in the atlantic large differences in frequency and intensity of tropical cyclone activity are seen both in the tropical atlantic as well as in the northwest caribbean and gulf of mexico depending on the mjo phase coherent changes in upper and lower level winds and relative humidity are likely responsible for these differences since the mjo shows potential predictability out to about two weeks the relationships discussed in this paper may be useful for short term predictions of the probability of tropical cyclone activity in the atlantic as a complement to the already available longer term seasonal predictions

analysis of the dominant mode of convectively coupled kelvin waves in the west african monsoon abstract the dominant mode of convectively coupled kelvin waves has been detected over the atlantic and africa during northern summer by performing composite analyses on observational fields based on an eof reconstructed convection index over west africa propagating eastward many waves originate from the pacific sector interact with deep convection of the marine itcz over the atlantic and the continental itcz over west and central africa and then weaken over east africa and the indian ocean it has been shown that they are able to modulate the life cycle and track of individual westward propagating convective systems their mean kinematic characteristics comprise a wavelength of 8000 km and a phase speed of 15 m s 1 leading to a period centered on 6 to 7 days the african kelvin wave activity displays large seasonal variability being highest outside of northern summer when the itcz is close to the equator facilitating the interactions between convection and these equatorially trapped waves the co

kelvin waves and tropical cyclogenesis a global survey abstractconvectively coupled atmospheric kelvin waves are among the most prominent sources of synoptic scale rainfall variability in the tropics but large uncertainties surround their role in tropical cyclogenesis this study identifies the modulation of tropical cyclones relative to the passage of a kelvin wave s peak rainfall i e its crest in each basin tropical cyclogenesis is generally inhibited for 3 days before the crest and enhanced for 3 days afterward composites of storms forming in the most favorable lags illustrate the dynamical impacts of the waves in most basins the tropical cyclone actually forms during the convectively suppressed phase of the wave the 850 hpa equatorial westerly anomalies provide the cyclonic vorticity for the nascent storm and 200 hpa easterly anomalies enhance the outflow the wind anomalies persist at both levels longer than the kelvin wave s period and are often related to the madden julian oscillation mjo the onset of these wind anomalies occurs with the

simulating speleothem growth in the laboratory determination of the stable isotope fractionation δ13c and δ18o between h2o dic and caco3 abstract here we present novel cave analogue experiments directly investigating stable carbon and oxygen isotope fractionation between the major involved species of the carbonate system hco3 co2 caco3 and h2o in these experiments which were performed under controlled conditions inside a climate box a thin film of solution flew down an inclined marble or glass plate after different distances of flow and thus residence times on the plate ph electrical conductivity supersaturation with respect to calcite precipitation rate as well as the 18o and 13c values of the dissolved inorganic carbon dic and the precipitated caco3 were obtained progressive precipitation of caco3 along the plate is accompanied by degassing of co2 and stable isotope fractionation and the system is driven out of isotope equilibrium we observe a strong enrichment of the 13c values with increasing residence time and a smaller enrichment in 18o the temporal evolution of the 18o and 13c values of both the dic and the precipitated caco3 can be explained by a rayleigh fractionation model but the observed enrichment in 13c values is much larger than expected based on isotope equilibrium fractionation factors our setup enables to determine the fractionation between caco3 and hco3 i e ecaco3 hco3 carbon isotope fractionation 13ecaco3 hco3 is strongly negative for all experiments and much lower than equilibrium isotope fractionation 0 1 in addition 13ecaco3 hco3 decreases with increasing residence time on the plate and thus decreasing supersaturation with respect to calcite thus isotope fractionation depends on precipitation rate and consequently occurs under kinetic conditions this is in contrast to previous studies which found no rate dependence and no or even a positive carbon isotope fractionation between caco3 and hco3 oxygen isotope fractionation 18ecaco3 hco3 is also negative and dependent on precipitation rate since no literature values for 18ecaco3 hco3 are available we calculated 18ecaco3 hco3 using equilibrium oxygen isotope fractionation factors between water and calcite and water and hco3 respectively at the beginning of the plate the fractionation is in agreement with the fractionation calculated using fractionation factors determined in cave systems the observed fractionation between caco3 and water 1000ln18 is also in good agreement with the values determined in cave systems and shows a very similar temperature dependence 1000 ln 18 16 516 1 267 10 3 t 26 141 4 356 however with progressive precipitation of caco3 along the plate the system is forced out of isotope equilibrium with the water and 1000ln18 increases the large negative rate dependent isotope fractionations observed in this study suggest that precipitation of speleothem calcite is strongly kinetically controlled and may thus have a large effect on speleothem 18o and 13c values since these values may erroneously be interpreted as reflecting changes in past temperature precipitation and or vegetation density these results have important implications for paleoclimate reconstructions from speleothems

what percentage of western north pacific tropical cyclones form within the monsoon trough abstractit is frequently stated that 70 80 of western north pacific tropical cyclones form within the monsoon trough but without an objective definition of the term several definitions are tested here when the monsoon trough mt is defined as the contiguous region where long term 1988 2010 mean july november 850 hpa relative vorticity is positive 73 of all july november tropical cyclones form within the mt this percentage varies interannually however from as low as 50 to nearly 100 the percentage correlates with the nino 3 4 index with more storms forming within the mt during warm periods when the mt is defined instead using long term monthly mean 850 more than 80 of tropical cyclones form within the mt in all months except july and august when more than 30 of storms form poleward of the mt it is hypothesized that the known peak in the frequency of upper tropospheric midlatitude wave breaking in july and august is responsible it is argued that any long term mean provides a suita

barotropic aspects of itcz breakdown abstract in satellite images the itcz intertropical convergence zone is sometimes observed to undulate and break down into a series of tropical disturbances tropical cyclones may later develop within these disturbances and move into higher latitudes allowing the itcz to reform it has been proposed that itcz breakdown results from a convectively modified form of combined barotropic and baroclinic instability of the mean flow an unstable mean flow can be produced by itcz convection in just a couple of days in this sense the itcz produces favorable conditions for its own instability and breakdown in this study a nonlinear shallow water model on the sphere is used to simulate barotropic aspects of itcz breakdown in the shallow water model the itcz is simulated by a prescribed zonally elongated mass sink near the equator the mass sink produces a cyclonic potential vorticity pv anomaly that has a reversed meridional pv gradient on its poleward side according to the ripa theorem a flow that has a