the representation of flows to partially penetrating rivers from layered and anisotropic aquifers abstract it has previously been shown that it is possible to represent the flow of water from a homogeneous isotropic aquifer to a river or drain by using a dupuit forcheimer groundwater flow model coupled with equations to calculate the magnitude of the flow to the river this work has now been extended to include anisotropic and layered aquifers results obtained from two dimensional free surface seepage models are used to assess the accuracy of the results from the dupuit forcheimer models it is shown that such models can be used to accurately estimate the flow to a river for a wide variety of situations

multiyear satellite observations of the atmospheric response to atlantic tropical instability waves 1 high resolution satellite measurements from the tropical rainfall measuring mission trmm quick scatterometer quikscat and special sensor microwave imager ssm i are used to study the variability of sea surface temperature sst surface wind velocity water vapor cloud liquid water and precipitation associated with westward moving tropical instability waves tiws in the atlantic ocean from 1998 to 2005 coherent ocean atmosphere patterns are shown during these 8 years southeasterly trades strengthen and water vapor increases over warm sst anomalies associated with tiws the opposite is true over cold tiw sst anomalies the cloud liquid water and rain response to the ssts follows a similar pattern appearing generally downstream of sst anomalies in the central tropical atlantic the atmospheric response to the tiw sst anomalies extends north of the tiw active region suggesting a remote response to the tiws the atmospheric response to the atlantic tiws also exhibits interannual variations in 1999 owing to the southward movement of the atlantic intertropical convergence zone itcz the rainfall response to the tiw sst anomalies is much larger than in other years when the atlantic itcz moves south it is more susceptible to tiw influence

quasi lagrangian large eddy simulations of cross equatorial flow in the east pacific atmospheric boundary layer using a large eddy simulation les the atmospheric boundary layer abl is numerically modeled along 958w from 88 st o 48n during boreal autumn and compared to observations from the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 since the local abl winds are predominantly southerly in this season a quasi lagrangian forcing is used in which the abl air column is forced as if it were advecting northward with the mean september october 2001 meridional wind across the equatorial cold tongue and the rapidly warming ssts to the north pressure gradients and large scale zonal advective tendencies are prescribed as a function of latitude where possible observations from the epic 2001 experiment are used for forcing and for comparison with model results the abl s modeled vertical structure accords with the conceptual model of wallace et al and agrees well with observations surface stability accounts for the minimum in surface wind over the equatorial cold tongue and the maximum over the warm water to the north stability of the lower abl over the cold tongue allows a jet to accelerate at about 500 m height relatively uncoupled to the frictional surface layer vertical mixing over the warm water to the north distributes this momentum to the surface additional simulations were performed to explore the modeled abl s sensitivity to pressure gradients zonal advection free tropospheric humidity and initial conditions the model abl was robust changing the forcings resulted in little change in the modeled structure the strongest sensitivity was of stratocumulus clouds over the cold tongue to cloud top radiative cooling once formed at the southern edge of the cold tongue modeled stratocumulus clouds demonstrate a remarkable ability to maintain themselves over the cold tongue in the absence of surface fluxes by radiative cooling at their tops the persistence of thin stratocumulus clouds in this lagrangian model suggests that horizontal advection of condensate might be an important process in determining cloudiness over the cold tongue

synoptic systems interacting with the rocky mountain barrier observations and theories abstractusing a composite analysis for strong sea level pressure perturbations off the west coast of north america the evolution of large amplitude synoptic systems upstream of the rocky mountains is investigated for the winter season corresponding previous analyses are refined by avoiding multiple counting of events and extended by including potential vorticity vertical motion and deformation in the analysis cyclonic and anticyclonic anomalies behave similarly with weak local extrema forming in the lee of the mountain range southeast of the parent systems however neither the geopotential anomaly nor the associated potential vorticity anomaly cross the mountain range nevertheless these anomalies contribute to the sea level pressure anomaly in the lee for both positive and negative anomalies potential vorticity exhibits a bipolar structure with lobes over the reference point and over the cordillera respectively the relevance of several theories describing the interaction between synoptic syste

the influence of sea surface temperature on surface wind in the eastern equatorial pacific weekly to monthly variability abstract temporal correlations between near equatorial surface wind and sea surface temperatures sst at 11 w in the eastern pacific ocean are investigated using data from an array of moored sensors between 5 n and 5 s the signature of tropical instability waves with periods of 20 30 days is apparent in time series of sst and both the meridional and zonal wind components results indicate the existence of a band of pronounced horizontal divergence in the surface wind field associated with the large meridional sst gradient equatorial front normally located just north of the equator perturbations of the equatorial front by the instability waves induce fluctuations in the overlying winds evidence of the air sea coupling is stronger in time series of the meridional gradients of wind and sst than between time series of the variables themselves the meridional differencing serves as a high pass filter in the space domain which removes planetary scale wind fluctuations that are unrelated to the local sst

coupled ocean atmospheric waves on the equatorial front striking 20 30 day sea surface temperature waves observed along the equatorial front in the later half of the year are generally believed to be of an oceanic origin here we report the detection of atmospheric waves that are unambiguously tied to these oceanic waves using new satellite measurements of surface winds a general circulation model simulation reveals that these atmospheric waves have a shallow vertical structure trapped in the planetary boundary layer pbl unlike el nino southern oscillation where changes in deep convection are the cause of anomalous winds vertical wave motion penetrates well above the pbl and is likely to impact the distribution and transport of climatically important gas species such as ozone and dimethyl sulfide

the representation of flows to partially penetrating rivers using groundwater flow models abstract although partially penetrating rivers have been successfully represented in groundwater flow models the assessment of the resistance coefficient in the equation used to calculate the flow between the aquifer and the river has always been a problem various methods have previously been presented but their derivations contain major assumptions in this paper the various methods are reviewed tested and found to be inaccurate a new more accurate method is presented and modifications are made to the existing methods to improve their accuracy finally a practical example of the use of the methods is given which shows that they can be applied to field problems with confidence

a new perspective of the climatological features of upper level cut off lows in the southern hemisphere this study presents a detailed view of the seasonal variability of upper level cut off lows cols in the southern hemisphere the cols are identified and tracked using data from a 36 year period of the european centre for medium range weather forecast reanalysis era interim the objective identification of the cols uses a new approach which is based on 300 hpa relative vorticity minima and three restrictive criteria of the presence of a cold core stratospheric potential vorticity intrusion and cut off cyclonic circulation the highest col activity is in agreement with previous studies located near three main continental areas australia south america and africa with maximum frequencies usually observed in the austral autumn the col mean intensity values show a marked seasonal and spatial variation with maximum minimum values during the austral winter summer a unique feature that has not been observed previously in studies based on the geopotential the link between intensity and lysis is examined and finds that weaker systems are more susceptible to lysis in the vicinity of the andes cordillera associated with the topographic rossby wave lysis and genesis regions are close to each other confirming that cols are quasi stationary systems also cols tend to move eastward and are faster over the higher latitudes the mean growth decay rates coincide with the major genesis and lysis density regions such as the significant decay values across the andes all year as a consequence of using vorticity for the tracking method a longer lifetime of cols is detected than in other studies but this does not affect the total frequency of occurrence comparisons with other studies suggest that the differences in seasonality are due to uncertainties in the reanalyses and the methods used to identify cols

local and remote atmospheric response to tropical instability waves a global view from space a la nina took place in the equatorial pacific in 1999 and strong tropical instability waves tiws developed causing large meanders of a sea surface temperature sst front between the equator and 3 n high resolution satellite measurements are used to describe the variability of sst surface wind velocity column integrated water vapor cloud liquid water and precipitation associated with these strong tiws in 1999 coherent ocean atmosphere patterns emerge in both the pacific and atlantic revealing rich regional characteristics in the far eastern pacific southeasterly trades strengthen weaken over positive negative sst anomalies apparently due to enhanced reduced mixing with high speed winds aloft in the central pacific we find evidence that sst induced sea level pressure changes also contribute substantially to wind fluctuations similar sst wind covariability also exists in the southern hemisphere along 2 s but the wind variability induced by unit sst anomaly is much larger than that north of the equator in the central pacific where the equatorial front is broad the northern sst pattern has a large meridional scale and reaches as far north as 6 n further to the north in the intertropical convergence zone itcz where local sst anomalies are small significant variability is found in clouds and precipitation which is further correlated with surface wind convergence in the atlantic tiw signals in sst are strongly trapped near the equator but they induce significant remote response in the itcz which takes a more southern position than its pacific counterpart and thus more susceptible to tiw influence

horizontal and vertical components of flow deduced from groundwater heads abstract this paper which supplements that of connorton 1985 shows how velocity components can be deduced from information about the groundwater head even though the groundwater head remains constant with depth it is possible to estimate both the vertical and horizontal flow components from the groundwater head distribution the accuracy of these calculated flow components can be assessed by comparing with results obtained from solutions in terms of the groundwater potential which is a function of both horizontal and vertical co ordinates examples considered include confined and unconfined aquifers aquifers having a sloping base and time variant behaviour a study of an aquifer with a horizontal band of lower hydraulic conductivity shows that in this situation the groundwater head approximation may not be acceptable

barometric pressure variations associated with eastern pacific tropical instability waves abstract barometric pressure surface temperature and wind time series in the eastern equatorial pacific are analyzed to determine if oceanic tropical instability wave tiw sea surface temperature variations cause barometric pressure gradients large enough to influence the atmospheric boundary layer during the study period from april 2001 to september 2002 11 tiws propagated westward past 110 w causing a spectral peak at 20 30 days in the sea surface temperature sst meridional difference between 2 n 110 w and 0 110 w likewise the meridional pressure difference also had a spectral peak in the 20 30 day tiw band cross spectral analysis shows that within the tiw band sst induced pressure variations were roughly 0 1 hpa c 1 in magnitude the resulting pressure gradient force is comparable in magnitude to other terms in the meridional momentum balance implications about the role of the boundary layer capping in the adjustment to sst forcing are discussed

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

the influence of sea surface temperature gradients on stratiform cloudiness along the equatorial front in the pacific ocean abstract satellite observations of visible cloudiness and sea surface temperature sst are used to test the hypothesis that the configuration of cool low level winds blowing across a sharp sst front in the equatorial eastern pacific gives rise to stratiform clouds on the warm downstream side of the front the results show that there is a maximum in low clouds over the equatorial front during the cold season of 1988 when the front and cross isotherm winds were strong the low cloud maximum was reduced in the warm el nino year of 1987 consistent with the weakening of the front instability waves along the equatorial front were pronounced during the summer and autumn of 1988 the results show a strong association between visible cloud and the sst waves with enhanced reduced cloudiness in the warm troughs cold crests of the waves

mathematical model of shallow water flow over porous media a conjunctive mathematical model for a surface subsurface flow system is developed the unsteady surface flow is explored by a set of one dimensional dynamic wave equations for shallow water which are solved by using a four point implicit finite difference scheme the transient subsurface flow is two dimensional with potential gradients in the vertical direction as well as the surface flow direction the porous medium may be saturated or unsaturated or both and it can be nonhomogeneous and anisotropic the subsurface flow equation is solved by employing a successive line over relaxation implicit finite difference scheme the surface and subsurface flow components are coupled at the ground surface considering the mass conservation and pressure relationships the model is verified by using existing experimental data and analytical solutions for special cases

the influence of sea surface temperature on surface wind in the eastern equatorial pacific seasonal and interannual variability abstract the climate of the eastern pacific exhibits a pronounced equatorial asymmetry boundary layer air originating in the southern hemisphere trades crosses the equator and flows into the intertropical convergence zone itcz whose southern limit is nearly always located at least 4 to the north of the equator the sea surface temperature sst distribution is characterized by a prominent cold tongue centered 1 s a strong frontal zone centered 2 n and a warm eastward current centered near 5 n the surface wind field exhibits a pronounced horizontal divergence as the air flows northward across the oceanic frontal zone these features vary in strength in response to the annual cycle and the el nino southern oscillation phenomenon the northward cross equatorial surface winds the cold tongue and the frontal zone all tend to be strongest during the cold season july through november during the cold season of the coldest years when the cold tongue is most prominent the cross equatorial flow t

coupling of groundwater and open channel flow abstract the paper describes an approach to incorporating drainage and the interaction of groundwater and open channel flow in a physically based hydrologic response model two classes of exchange are distinguished the first is concerned with the influence of minor conduits which require too much refinement to be modelled on an individual basis but amalgamated make an important contribution to the water budget of a region on an areal basis the second class of exchange is direct seepage from or into the larger waterways in which the flow is significant and is modelled as a distinct hydrologic process in the first part of the paper a theory for treating the exchange phenomena is developed the basis is formed by the hooghoudt ernst formula of drainage design and the theory of additional seepage resistances the remainder of the paper is devoted to the technical implementation of this theory a number of practical steps to limit the data and organization required are outlined the main technical hurdle dealt with is the coupling of the two fundamentally incompatible numerical schemes for groundwater and open channel flow in such a way that a conservative water balance is maintained details of the complete hydrologic response model are presented as an appendix

atmospheric response to atlantic tropical instability waves in community atmosphere model version 3 1 tropical instability waves tiws are 20 to 40 day waves that appear along the sea surface temperature sst front of the equatorial cold tongues in this study we investigate the atmospheric planetary boundary layer response to tiw induced sst variations in the tropical atlantic ocean using community atmosphere model version 3 cam3 developed at the national center for atmospheric research and compare the model simulation with available satellite measurements cam3 is used to simulate the response to atlantic tiws with t85 and t42 horizontal resolutions forced with daily tropical rainfall measuring mission microwave imager tmi ssts and t85 horizontal resolution forced with weekly tmi and reynolds ssts all four runs exhibit an atmospheric response to the sst anomalies but the amplitude of the response is different in each case the model simulates winds convergence column integrated water vapor and precipitation perturbations associated with tiws that are similar in many respects to the satellite observations however the wind convergence and divergence anomalies in the satellite observations are located west of the sst anomalies in the cam3 simulations the wind convergence is more in phase with sst anomalies differences between the observations and the model simulations appear to be due to both differences in the boundary layer response and differences in the horizontal advection process

a numerical modeling study of warm offshore flow over cool water abstract numerical simulations of boundary layer evolution in offshore flow of warm air over cool water are conducted and compared with aircraft observations of mean and turbulent fields made at duck north carolina two models are used a two dimensional high resolution mesoscale model with a turbulent kinetic energy closure scheme and a three dimensional large eddy simulation les model that explicitly resolves the largest turbulent scales both models simulate general aspects of the decoupling of the weakly convective boundary layer from the surface as it is advected offshore and the formation of an internal boundary layer over the cool water two sets of experiments are performed which indicate that complexities in upstream surface conditions play an important role in controlling the observed structure the first land sea experiments examine the transition from a rough surface having the same temperature as the ambient lower atmosphere to a smooth ocean surface that is 5 c cooler in the seco

tropical instability wave kinematics observations from the tropical instability wave experiment the kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measurements from an array of acoustic doppler current profilers deployed in the equatorial pacific during the tropical instability wave experiment a distinctive wave season was observed from august to december 1990 with wave energy confined primarily above the core of the equatorial undercurrent particle motions in the horizontal plane are described by eccentric ellipses oriented toward the north but tilting into the cyclonic shear of the south equatorial current the tilt is maximum near the surface just north of the equator and decreases to the south and with depth the distribution of wave variance is narrowband in both frequency and zonal wavenumber with central period zonal wavelength and westward directed phase propagation estimated to be 500 hours 1060 km and 59 cm s 1 respectively neither the meridional nor the vertical wavenumber component is statistically different from zero these results generally agree with previous findings on tropical instability waves from the atlantic and pacific oceans and in the undersampled arena of geophysical measurements they provide an example where statistical inference is supported by an ensemble of independent measurements

lee cyclogenesis part i analytic studies abstract the growth of synoptic scale cyclones imbedded in a baroclinically unstable zonal flow over a long straight mountain range is investigated two different analytical models of the phenomenon are used the first model uses the linearized quasi geostrophic equations it allows a simple superposition of a steady state mountain forced solution and a transient eady wave there is no dynamic interaction between the two solutions but the time evolution of the combined solution reproduces many characteristics of a disturbance passing over the rocky mountains the semigeostrophic equations are used in the second model these equations allow a linear solution in transform space but the transformation of the solution to physical space is nonlinear this allows an interaction between the mountain forced and transient solutions the minimum pressure developed by the semigeostrophic system is the same as that of the quasi geostrophic system however the shape of the wave is distorted this effect is caused b

atmospheric manifestation of tropical instability wave observed by quikscat and tropical rain measuring mission observations from two new spaceborne microwave instruments in 1999 clearly reveal the atmospheric manifestation of tropical instability waves north of the pacific equatorial cold tongue a unique zonal temporal band pass filter enables the isolation of the propagating signals and the determination of their phase differences the phase differences between the propagation of wind and sea surface temperature sst signals observed from space and the vertical wind profiles measured from a research ship are consistent with the hypothesis that the coupling between wind and sst is caused by buoyancy instability and mixing which reduces the wind shear in the atmospheric boundary layer the coupling causes higher evaporative cooling over the warm phase and infers a negative thermal feedback

observations of 20 day period meridional current oscillations in the upper ocean along the pacific equator abstract prominent oscillations of the meridional current with a mean period of approximately 20 days have been observed in the upper ocean over several years from may 1979 to october 1985 using moored current measurements along the pacific equator at 95 110 124 140 w and 152 w as well as off but near the equator at 110 and 140 w the fluctuations are relatively narrowband 0 005 cpd in frequency a 95 statistically significant peak in power spectra of meridional current occurred at 110 124 and 140 w but not at 95 and 152 w where the spectral peaks were smaller the dominant wave period decreased by about 4 from 110 to 140 w maximum amplitude was measured at 124 w the amplitude above 80 m was maximum at the equator and decreased poleward from the equator at 15 m the annual averaged root mean square amplitude was about 20 5 cm s 1 and individual peak to trough values reached 150 cm s 1 the wave amplitude decreased with depth and the wave was essentially confined to the upper 80 m