the role of barents sea ice in the wintertime cyclone track and emergence of a warm arctic cold siberian anomaly abstractsea ice variability over the barents sea with its resultant atmospheric response has been considered one of the triggers of unexpected downstream climate change for example east asia has experienced several major cold events while the underlying temperature over the arctic has risen steadily to understand the influence of sea ice in the barents sea on atmospheric circulation during winter from a synoptic perspective this study evaluated the downstream response in cyclone activities with respect to the underlying sea ice variability the composite analysis including all cyclone events over the nordic seas revealed that an anticyclonic anomaly prevailed along the siberian coast during light ice years over the barents sea this likely caused anomalous warm advection over the barents sea and cold advection over eastern siberia the difference in cyclone paths between heavy and light ice years was expressed as a warm arctic cold siberian wacs anomaly the lower baroclinicity over the barents se

sea surface temperature in the north tropical atlantic as a trigger for el nino southern oscillation events the el nino southern oscillation in the pacific ocean influences temperature in other tropical ocean basins reanalysis data and model simulations suggest that temperature anomalies in the north tropical atlantic may also influence the development of la nina events

dominant interannual and decadal variability of winter surface air temperature over asia and the surrounding oceans to clarify the interannual variability of winter surface air temperature sat over asia and the surrounding oceans the authors applied principal component analysis to normalized monthly sats the first mode represents the asian north south dipole pattern with a node over the tibetan plateau this component has close relationships to the arctic oscillation and cold surge variability around southeast asia showing decadal oscillation with signal changes in 1988 and 1997 the second mode is the inner asian mode with a center to the north of the tibetan plateau this component connects to fluctuations of not only the western siberian high but also the icelandic low which is associated with the pattern of the polar vortex over eurasia a recent warming trend and possible relationship to solar activity are also shown the modes of asian sat variability associated with enso are extracted as the north south dipole mode over the tropical western pacific and japan the third mode and silk road mode the fourth mode the two independent modes appear to be caused by different sea surface temperature sst anomalies over the western pacific and indian ocean and their associated atmospheric rossby wave responses the atmospheric wave trains over both the north and south of the tibetan plateau in the third mode and the atmospheric wave train that propagates toward the silk road via greenland in the fourth mode

changes in the relationship between northeast china summer temperature and enso 1 northeast china nec summer temperature tends to be lower higher than normal in el nino la nina developing years during 1950s through mid 1970s the relationship between the nec summer temperature and el nino southern oscillation enso is weakened or even becomes opposite in 1980s and 1990s the present study documents this interdecadal change and investigates plausible reasons for this change before the late 1970s enso affects the nec summer temperature through modulating the south asian heating and consequently the midlatitude asian circulation after the late 1970s the connection between enso and the indian summer monsoon and that between the south asian heating and the midlatitude asian circulation have been weakened this leads to a weakening of enso impacts on the nec summer temperature it is found that the nec summer temperature variations are closely related to the north atlantic sea surface temperature sst and circulation changes in 1980s and 1990s in particular a tripole north atlantic sst anomaly pattern in boreal spring is a good precursory for the nec summer temperature anomalies the nec summer temperature displays a negative correlation with the summer sst surrounding the maritime continent in 1980s and 1990s in many years the tropical north pacific and the north atlantic sst anomalies can contribute in concert to the midlatitude asian circulation changes and the nec summer temperature anomalies these effects overcome those of the central and eastern equatorial pacific sst anomalies leading to a same sign relationship between the nec summer temperature and the central and eastern equatorial pacific sst anomalies

stratocumulus cloud top height estimates and their climatic implications a depth dependent boundary layer lapse rate was empirically deduced from 156 radiosondes released duringsixmonth longresearchcruisestothe southeastpacificsamplingavarietyofstratocumulusconditions thelapse ratedependenceonboundarylayerheightisweak decreasingfromabestfitof7 6to7 2k km 21 as theboundarylayerdeepensfrom800mto2km ship basedcloud baseheightsupto800mcorrespondwellto liftingcondensationlevels indicatingwell mixedconditions withcloud bases 800moften 200 600m higher than the lifting condensation levels the lapse rates were combined with moderate resolution imaging spectrometer 11 mm derived cloud top temperatures and satellite microwave derived sea surface temperatures to estimate stratocumulus cloud top heights the october mean cloud top height structure of the southeast pacific was then spatially and diurnally characterized coastal shoaling is apparent but so is a significant along coast cloud top height gradient with a pronounced elevation of the cloud top heights above thearicabightat 208s diurnalcloud topheightvariations inferredfromirregular4 times dailysampling can locally reach 250 m in amplitude and they can help to visualize offshore propagation of free tropospheric vertical motions a shallow boundary layer associated with the chilean coastal jet expands to its north and west in the afternoon cloud top heights above the arica bight region are depressed in the afternoon which may mean that increased subsidence from sensible heating of the andes dominates an afternoon increase in convergence upward motion at the exit of the chilean coastal jet in the southeast atlantic during october thestratocumuluscloud topheightsaretypicallylowerthanthoseinthesoutheastpacific acoastaljetregion can also be identified through its low cloud top heights coastal shoaling of the south atlantic stratocumulus region is mostly uniform with latitude in keeping with the more linear namibian angolan coastline the southeast atlantic shallow cloudy boundary layer extends farther offshore than in the southeast pacific particularly at 158s

relationship between the indian monsoon rainfall and the tropospheric temperature over the eurasian continent based on climatological data such as the all india rainfall air for 1949 98 air temperatures in the troposphere and at the land surface for 1949 98 as well as precipitation and outgoing long wave radiation olr for 1979 98 the statistical relationship between the indian monsoon rainfall and tropospheric temperature tt over the eurasian continent is examined by using the correlation analysis and singular value decomposition svd analysis methods the main results are summarized as follows 1 the june september jjas air has significant positive correlations with the 200 700 hpa tt averaged for eurasia in jjas the area with the highest simultaneous correlation of upper tt with air for jjas is located in western eurasia there is also a region with positive simultaneous correlations in the southern subtropics covering southern africa the jjas air also shows significant positive correlations with tt over the eurasian continent in march may mam and with the tt averaged over the tibetan plateau in september and october although some precursory springtime temperature signals for the anomalous summer monsoon are found in the upper tt over eurasia the variation in the upper tt appears mostly independent from that of the land surface temperature 2 the anomalies of upper tt in jjas are closely coupled with the variations in olr related to the monsoon rainfall over tropical asia and africa the spatial structure of the first svd mode for olr anomalies shows the coherent variations in convective activity from northern tropical africa to india while the pattern of the first svd mode for 300 hpa temperature anomalies shows a distribution which is nearly symmetric with respect to the equator with variations of the same sign over subtropical areas in both hemispheres and variations of the opposite sign around equatorial africa this pair of coupled patterns suggests that when the monsoon rains from tropical africa to india become more intense the upper troposphere from northern africa to western asia and over southern africa becomes warmer 3 the observed temperature variation in the upper troposphere over the eurasian continent especially western eurasia during the summer monsoon season is considered to be a result of the anomalous subsidence and thermal advection dynamically induced by anomalous tropical heating associated with the enhanced monsoon rainfall this study suggests that the tropical convective activity linked to the indian monsoon rainfall has an impact on the atmospheric variability on a global scale

view angle dependence of cloud optical thicknesses retrieved by moderate resolution imaging spectroradiometer modis 1 this study examines whether cloud inhomogeneity influences the view angle dependence of modis cloud optical thickness retrieval results the degree of cloud inhomogeneity is characterized through the local gradient in 11 m brightness temperature the analysis of liquid phase clouds in a 1 year long global data set of collection 4 modis data reveals that while optical thickness retrievals give remarkably consistent results for all view directions if clouds are homogeneous they give much higher values for oblique views than for overhead views if clouds are inhomogeneous and the sun is fairly oblique the mean optical thickness retrieved for the most inhomogeneous third of cloudy pixels is more than 40 higher for oblique views than for overhead views if the solar zenith angle exceeds 60 after considering a variety of possible scenarios the paper concludes that the most likely reason for the increase lies in three dimensional radiative interactions that are not considered in current one dimensional retrieval algorithms namely the radiative effect of cloud sides viewed at oblique angles seems to contribute most to the enhanced optical thickness values the results presented here will help understand and estimate cloud retrieval uncertainties related to cloud inhomogeneity and may eventually help correct for the observed view angle dependent biases

observations of three dimensional radiative effects that influence modis cloud optical thickness retrievals abstract when cloud properties are retrieved from satellite observations current calculations apply one dimensional 1d theory to the three dimensional 3d world they consider only vertical processes and ignore horizontal interactions this paper proposes a novel approach that estimates 3d effects in cloud optical thickness retrievals the proposed method combines visible and thermal infrared images to see whether 3d radiative effects make clouds appear asymmetric that is whether cloud surfaces tilted toward the sun are systematically brighter than surfaces tilted away from it the observed asymmetries are then used to estimate 3d effects for 1 km size pixels as well as 50 km size areas initial results obtained for moderate resolution imaging spectroradiometer modis images reveal that 3d effects cause abundant uncertainties in the 1 km resolution 1d retrievals averaging over 50 km by 50 km areas greatly reduces the errors but does not remove them completely conservative estimates show that the m

a link between reduced barents kara sea ice and cold winter extremes over northern continents the recent overall northern hemisphere warming was accompanied by several severe northern continental winters as for example extremely cold winter 2005 2006 in europe and northern asia here we show that anomalous decrease of wintertime sea ice concentration in the barents kara b k seas could bring about extreme cold events like winter 2005 2006 our simulations with the echam5 general circulation model demonstrate that lower troposphere heating over the b k seas in the eastern arctic caused by the sea ice reduction may result in strong anti cyclonic anomaly over the polar ocean and anomalous easterly advection over northern continents this causes a continental scale winter cooling reaching 1 5 c with more than three times increased probability of cold winter extremes over large areas including europe our results imply that several recent severe winters do not conflict the global warming picture but rather supplement it being in qualitative agreement with the simulated large scale atmospheric circulation realignment furthermore our results suggest that high latitude atmospheric circulation response to the b k sea ice decrease is highly nonlinear and characterized by transition from anomalous cyclonic circulation to anticyclonic one and then again back to cyclonic type of circulation as the b k sea ice concentration gradually reduces from 100 to ice free conditions we present a conceptual model which may explain the nonlinear local atmospheric response in the b k seas region by counter play between convection over the surface heat source and baroclinic effect due to modified temperature gradients in the vicinity of the heating area

reflected solar radiances from broken cloud scenes and the interpretation of scanner measurements if an adequate model of the reflection characteristics of a given scene is available the reflected solar irradiance from the scene may be determined from radiance measurements made by satellite borne scanning radiometers a theoretical analysis of the reflection functions of broken cloud scenes is presented using monte carlo simulations of the radiative transfer in various three dimensional geometries it is shown that the reflection functions of horizontally extensive stratiform and horizontally limited cumuliform clouds are generally quite different the differences are greatest for nadir and limb views but tend to vanish for reflected radiances with a zenith angle of 60 deg applications to satellite observations suggest potential errors of a factor of 2 in the inferred irradiance are likely due to scene misidentification when the radiances are interpreted indiscriminantly selection of preferred satellite viewing directions however can significantly reduce this error

northeast china summer temperature and north atlantic sst a previous study revealed a close relationship between interannual variations ofnortheast china nec summer temperature and a tripole sea surface temperature sst anomaly pattern in the north atlantic in preceding spring the present study investigatesthe change in the above relationship and the plausible causes for the change a tripole sstindex is defined with its positive value corresponding to positive sst anomalies in thetropics and midlatitudes and negative sst anomalies in the subtropics the tripole sstanomaly pattern has a weak correlation with nec summer temperature during the 1950sthrough the mid 1970s in sharp contrast to the 1980s and 1990s this change is related tothe difference in the persistence of the tripole sst pattern before the late 1970s thetripole sst pattern weakened from spring to summer and thus the spring north atlantictripole sst pattern had a weak connection with nec summer temperature on thecontrary after the late 1970s the tripole sst pattern displayed a tendency of persistencefrom spring to summer contributing to circulation changes that affected nec summertemperature there are two factors for the persistence of the tripole sst pattern fromspring to summer one is the north atlantic air sea interaction and the other is thepersistence of sst anomalies in the eastern equatorial pacific during the decay ofel nino southern oscillation enso it is shown that the north atlantic sst anomaliescan have an impact on nec summer temperature independent of enso

case study of inhomogeneous cloud parameter retrieval from modis data 1 cloud parameter retrieval of inhomogeneous and fractional clouds is performed for a stratocumulus scene observed by modis at a solar zenith angle near 60 the method is based on the use of neural network technique with multispectral and multiscale information it allows to retrieve six cloud parameters i e pixel means and standard deviations of optical thickness and effective radius fractional cloud cover and cloud top temperature retrieved cloud optical thickness and effective radius are compared to those retrieved with a classical method based on the homogeneous cloud assumption subpixel fractional cloud cover and optical thickness inhomogeneity are compared with their estimates obtained from 250m pixel observations this comparison shows a fairly good agreement the cloud top temperature appears also retrieved quite suitably

observed interannual oscillations of planetary wave forcing in the northern hemisphere winter 1 using ncep ncar reanalysis data from 1958 to 1998 two interannual oscillations in the eddy forcing due to planetary waves wavenumbers 1 3 are found in the northern hemisphere winter called as the stratospheric interannual oscillation sio and the tropospheric interannual oscillation tio the temporal evolutions are different between the sio and the tio suggesting different dynamic mechanisms the planetary waves tend to be bent equatorward in the troposphere during a positive tio phase and in the mid and upper stratosphere during a positive sio phase the result also suggests that upward propagation of planetary waves into the polar waveguide across the tropopause is closely associated with the tio further regression and correlation analyses suggest that the tio is closely linked to the northern annular mode nam whereas the sio is closely associated with the el nino southern oscillation enso

inference of marine stratus cloud optical depths from satellite measurements does 1d theory apply abstract the validity of plane parallel 1d radiative transfer theory for cloudy atmospheres is examined by directly comparing calculated and observed visible reflectances for one month of global area coverage advanced very high resolution radiometer satellite observations of marine stratus cloud layers off the coasts of california peru and angola marine stratus are an excellent testbed as they arguably are the closest to plane parallel found in nature optical depths in a 1d radiative transfer model are adjusted so that 1d model reflectances match those observed at nadir on a pixel by pixel basis the 1d cloud optical depth distributions are then used in the plane parallel model to generate reflectance distributions for different sun earth satellite viewing geometries these reflectance distributions are directly compared with the observations separate analyses are performed for overcast and broken cloud layers as identified by the spatial coherence method when 1d reflectances are directly compare

the potential for improved boundary layer cloud optical depth retrievals from the multiple directions of misr abstract the multiangle imaging spectroradiometer misr views the earth with nine cameras ranging from a 70 zenith angle viewing forward through nadir to 70 viewing aft misr does not have an operational cloud optical depth retrieval algorithm but previous research has hinted that solar reflection measured in multiple directions might improve cloud optical depth retrievals this study explores the optical depth information content of misr s multiple angles using a retrieval simulation approach hundreds of realistic boundary layer cloud fields are generated with large eddy simulation les models for stratocumulus small trade cumulus and land surface forced fair weather cumulus reflectances in misr directions are computed with three dimensional radiative transfer from the les cloud fields over an ocean surface and averaged to misr resolution and sampled at misr 275 m pixel spacing neural networks are trained to retrieve the mean and standard deviation of optical depth over different size pixel pa

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

influence of low arctic sea ice minima on anomalously cold eurasian winters 1 influence of low arctic sea ice minima in early autumn on the wintertime climate over eurasia is investigated observational evidence shows that significant cold anomalies over the far east in early winter and zonally elongated cold anomalies from europe to far east in late winter are associated with the decrease of the arctic sea ice cover in the preceding summer to autumn seasons results from numerical experiments using an atmospheric general circulation model support these notions the remote response in early winter is regarded as a stationary rossby wave generated thermally through an anomalous turbulent heat fluxes as a result of anomalous ice cover over the barents kara seas in late autumn which tends to induce an amplification of the siberian high causing colder conditions over the far east the late winter cold anomalies over eurasia are also reproduced in our experiment which is associated with the negative phase of the north atlantic oscillation

impacts of early autumn arctic sea ice concentration on subsequent spring eurasian surface air temperature variations this study reveals a close relation between autumn arctic sea ice change sic in the laptev sea eastern siberian sea beaufort sea and subsequent spring eurasian surface air temperature sat variation specifically more less sic over the above regions in early autumn generally correspond to sat warming cooling over the mid high latitudes of eurasia during subsequent spring early autumn arctic sic affects spring eurasian sat via modulating spring arctic oscillation ao associated atmospheric changes the meridional temperature gradient over the mid high latitudes decreases following the arctic sea ice loss this results in deceleration of prevailing westerly winds over the mid latitudes of the troposphere which leads to increase in the upward propagation of planetary waves and associated eliassen palm flux convergence in the stratosphere over the mid high latitudes thereby westerly winds in the stratosphere are reduced and the polar vortex is weakened through the wave mean flow interaction and downward propagation of zonal wind anomalies a negative spring ao pattern is formed in the troposphere which favors sat cooling over eurasia the observed autumn arctic sic spring eurasian sat connection is reproduced in the historical simulation 1850 2005 of the flexible global ocean atmosphere land system model spectral version 2 fgoals s2 the fgoals s2 also simulates the close connection between autumn sic and subsequent spring ao further analysis suggests that the prediction skill of the spring eurasian sat was enhanced when taking the autumn arctic sic signal into account

relationship between ural siberian blocking and the east asian winter monsoon in relation to the arctic oscillation and the el nino southern oscillation this study attempts to assess the possible linkage between ural siberian blocking and the east asian winter monsoon eawm during the boreal winter the dominance of blocking thermally enhances cold advection downstream the frequent occurrence of ural siberian blocking potentially promotes a cold eawm and vice versa the seasonal blocking activity can be regarded as the combined effect of the arctic oscillation ao and the el nino southern oscillation enso weakened strengthened meridional flow in the positive negative phase of the ao is unfavorable favorable for the formation of blocking highs because the ao shows a close relationship with the north atlantic oscillation nao its teleconnection with ural siberian blocking may exist in the form of an eastward propagating wave train be that as it may the wave train signal across east asia may be disturbed by the external effect of a strong enso event which probably enhances weakens the westerlies near siberia in its warm cold phase consequently the blocking eawm relationship is stronger weaker when the ao and enso are in phase out of phase if both ao and enso attain the positive negative phase the siberian high tends to be weaker stronger and the temperature tends to be higher lower in east asia with less more ural siberian blocking on the other hand if they are out of phase they are not strongly linked to the intensity of the siberian high and the blocking activity over ural siberia is unclear

neural network retrieval of cloud parameters of inhomogeneous clouds from multispectral and multiscale radiance data feasibility study 1 in this paper we investigated the feasibility of retrieving cloud parameters of inhomogeneous and fractional clouds from simulated multispectral and multiscale radiometric data by using mapping neural networks a radiometric database prepared for neural network training consists of area averaged radiance data for two pixel scales i e 1 km 1 km and 0 25 km 0 25 km pixels respectively the cloud parameter retrieval assumes a vertically uniform inhomogeneous and fractional cloud defined with 6 parameters i e the mean and standard deviation of optical thickness the mean and standard deviation of effective radius the fractional cloud cover and the cloud top temperature all defined at a scale of cloud parameter retrieval the retrieval procedure comprises two separate steps the first one is relative to the angular interpolation and correction of radiance data surface reflection and thermal emission contribution the second step concerns the cloud parameter retrieval as such from interpolated and corrected radiance data the input vector to the retrieval mnns consists of 8 radiometric data in addition to a number of necessary ancillary data such as surface temperature and ground albedo the 8 radiometric data are 5 area averaged radiances over 1 km 1 km pixel and 3 standard deviations of radiance over 1 km 1 km pixel estimated from 0 25 km 0 25 km pixel radiances after evaluating the performance of the neural networks trained for each step we tested the whole retrieval procedure for three types of inhomogeneous and fractional clouds flat top bounded cascade clouds and flat top and non flat top gaussian process clouds all the cloud parameters of these clouds can be retrieved with reasonable accuracy in spite of the fact that the mean and standard deviation of optical thickness of non flat top clouds exhibit some dispersion the inclusion of 0 25 km 0 25 km pixel radiance data as input vector components improved significantly the performance of the cloud parameter retrieval finally we analyzed the consequences of some simplifying assumptions on the retrieved cloud parameters and discussed the perspectives of the cloud parameter retrieval based on the neural networks

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

interannual variations of stationary planetary wave activity in the northern winter troposphere and stratosphere and their relations to nam and sst 1 with the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data from 1958 to 1998 two teleconnection patterns in the eliassen palm ep flux divergence field due to stationary planetary waves with wavenumbers wns 1 to 3 are studied in the northern hemisphere winter both patterns appear as dipole structures with divergence of ep flux in the north and convergence in the south or vice versa one dipole evolves mainly in the stratosphere and is referred to as the stratospheric interannual oscillation sio the other evolves mostly in the troposphere and is referred to as the tropospheric interannual oscillation tio the tio and the sio are shown to be associated with anomalous meridional planetary wave propagation in the troposphere and stratosphere respectively the upward and poleward refraction of planetary waves into the polar waveguide across the tropopause is closely linked to the tio examination of individual waves indicates that the tropospheric dipole ofep flux divergence comes basically from wn 3 whereas the stratospheric one comes totally from wns 1 and 2 the reduced refraction of planetary waves into the polar waveguide across the tropopause associated with positive tio index is dominantly contributed from both wns 1 and 2 regression and correlation analyses suggest that the tio is closely related to the northern annular mode nam its relation to the sea surface temperature sst is consistent with previous studies on the relation of nam to sst on the other hand the sio is shown to be closely associated with anomalous zonal mean winds in the subtropics of the midstratosphere and has a moderate correlation with an augmented pacific north american pna pattern in 500 hpa geopotential height for the leading eof of stratospheric u variability the sio accounts for a smaller fraction than the tio however with the teleconnectivity in stratospheric ep flux divergence one can distinguish a stratospheric variation of anomalous north south planetary wave propagation from the total amount of wave activity entering the stratosphere which may help us to understand the variability of transport circulation in the stratosphere significant correlation of sio with tropical sst reveals that tropical sst is leading the sio by up to around 9 months which suggests a strong impact of el nino southern oscillation enso on the sio planetary waves tend to be bent poleward in the midstratosphere when there is a warm event the situation tends to be reverse during a cold event

increased eurasian tropical temperature amplitude difference in recent centuries implications for the asian monsoon 1 a warmer eurasian continent and stronger land sea temperature gradient between eurasia and the tropical oceans contribute to an intensified summer monsoon we evaluate changes in the temperature difference between eurasia and the tropics over 250 years using proxies of eurasian surface air temperatures tree rings and tropical sea surface temperatures indo pacific corals these records show low frequency correspondence with each other over this interval and with other temperature and precipitation sensitive proxies from the asian monsoon regime greater warming is estimated for eurasia amplitude 1 70 0 28 c 1801 20 vs 1976 95 relative to the tropics 0 61 0 29 c 1806 25 vs 1937 56 the amplitude change from the 18th to 20th centuries is thus estimated to be about three times 1 5 6 greater over eurasia than the tropics this change may have contributed to an intensified asian monsoon system over recent centuries and to a decoupling of the monsoon and el nino southern oscillation in recent decades

spring arctic oscillation east asian summer monsoon connection through circulation changes over the western north pacific in the present study the links between spring arctic oscillation ao and east asian summer monsoon easm was investigated with focus on the importance of the north pacific atmospheric circulation and sea surface temperature sst to reduce the statistical uncertainty we analyzed high pass filtered data with the inter annual time scales and excluded the el nino southern oscillation signals in the climate fields using a linear fitting method the significant relationship between spring ao and easm are supported by the changes of multi monsoon components including monsoon indices precipitation and three dimensional atmospheric circulations following a stronger positive spring ao an anomalous cyclonic circulation at 850 hpa appears in southeastern asia and the western north pacific in summer with the easterly anomalies spanning from the pacific to asian continent along 25 n 30 n and the westerly anomalies south of 15 n at the same time the summer western north pacific subtropical high becomes weaker consistently the positive precipitation anomalies are developed over a broad region south of 30 n stretching from southern china to the western pacific and the negative precipitation anomalies appear in the lower valley of the yangtze river and southern japan the anomalous cyclone in the western north pacific persisting from spring to summer plays a key role in modulating easm and monsoon precipitation by a positive air sea feedback mechanism during spring the ao associated atmospheric circulation change produces warmer ssts between 150 e 180 near the equator the anomalous sensible and latent heating in turn intensifies the cyclone through a gill type response of the atmosphere through this positive feedback the tropical atmosphere and sst patterns sustain their strength from spring to summer that consequently modifies the monsoon trough and the western north pacific subtropical high and eventually the easm precipitation moreover the sst response to ao circulation is supported by the numerical simulations of an ocean model and the anomalous atmospheric circulation over the western north pacific is also reproduced by the dedicated numerical simulations using the coupled atmosphere ocean model the observation evidence and numerical simulations suggest the spring ao can impact the easm via triggering tropical air sea feedback over the western north pacific

decadal variations of the relationship between the summer north atlantic oscillation and middle east asian air temperature 1 the relationship between the summer july september north atlantic oscillation snao and simultaneous east asian air temperature is investigated the results show that the snao is related to middle east asian summer air temperature however this linkage varies with time on decadal timescale a strong connection appears after the late 1970s but a weak connection before the late 1970s further analysis indicates that this instable relationship may have resulted from the shift of the snao mode around the late 1970s in the period of 1979 2003 the centers of the snao mode are located more eastward a positive phase negative phase snao produces a strong lower level divergence convergence over the asian jet entrance region in turn stimulates a strong upper level convergence divergence via the ekman pumping such a convergence divergence then excites a zonally oriented quasi stationary barotropical rossby wave train along the asian upper level jet thus the snao signal is transported eastward to east asia resulting in an anomalous summer air temperature over middle east asia however in the period of 1951 1975 the centers of the snao mode are located more westward the associated upper level divergence convergence is away from the asian jet entrance region and the snao signal cannot be transported eastward to east asia hence the connection is broken

change in the contribution of spring snow cover and remote oceans to summer air temperature anomaly over northeast china around 1990 sea surface temperature sst snow cover and soil moisture anomalies are factors for climate variability over land regions the present study found that the relationship between in situ spring snow cover and northeast china summer surface temperature variations is not steady it is significant during mid 1970s through late 1980s but weak during the 1990s and 2000s this interdecadal change in the spring snow cover summer temperature relationship is found to relate to the effects of sst anomalies in the tropical indian ocean and western pacific regions during the recent decades these sst anomalies induce a meridional circulation pattern along the east asian coast the remote sst forcing induced circulation and precipitation anomalies overcome local snow cover induced soil moisture anomalies and thus disrupt the spring snow cover summer temperature connection during the recent decades the present study indicated that both the north atlantic sst anomaly pattern and local spring snow cover anomalies contribute to northeast china summer temperature variations during mid 1970s through late 1980s during the 1990s and 2000s the influence of the north atlantic sst anomalies is weakened and the sst anomaly in the tropical indo western pacific region is a major player in northeast china summer temperature variations

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

use of misr measurements to study the radiative transfer of an isolated convective cloud implications for cloud optical thickness retrieval 1 radiative transfer simulations of an isolated deep convective cloud reconstructed with stereo techniques from the multiangle imaging spectroradiometer misr are compared with the reflectances measured at the nine misr viewing angles the simulations were done using a three dimensional monte carlo model in which ocean reflectance aerosol and rayleigh scattering were prescribed to match the surrounding clear sky misr measurements making reasonable assumptions regarding the vertical and horizontal distribution of the volume extinction coefficient we were able to reproduce the misr measurements with the 3d radiative calculations while the uniqueness of the these distributions cannot be proven they all lead to retrievals of much larger cloud optical thickness and cloud water content than for a 1d retrieval averaged over the cloud the difference was a factor of about 3 rising to 9 locally this is a consequence of horizontal photon transport that serves to highlight the inadequacy of 1d retrievals for the case of deep convective cloud concerning the internal cloud properties we noticed the angular distribution of modeled radiances did not match the measured radiances when an ice crystal phase function was applied better estimates of the optical depths and water contents of deep convective clouds appear to be obtainable by integrating an estimate of the extinction coefficient over the vertical cloud extent when this can assessed than by attempting to invert the radiance measured from a single angle view using 1d theory