observational evidence from direct current measurements for propagation of remotely forced waves on the shelf off the west coast of india 1 we use data from six acoustic doppler current profiler adcp moorings deployed during march september 2008 on the continental shelf and slope off bhatkal goa and jaigarh on the central west coast of india to present evidence for poleward propagation of shelf or coastal trapped waves ctws wave propagation is seen on the shelf in the 20 40 day 10 14 day and 3 5 day period bands the lag from south to north indicates that remote forcing is important even at periods as short as 4 days using quikscat wind data we show that the contribution of remote forcing to the shelf west indian coastal current wicc is significant even when the local alongshore wind is strong as during the summer monsoon onset during may june and forces a strong local response that masks the effect of remote forcing forced wave calculations using ctw theory show that remote forcing of the wicc is present at all times but is most striking when the local winds are weak as during march april the ctw calculations show that the source region for the remote forcing may extend beyond the west coast into the gulf of mannar between india and sri lanka on the slope propagation is seen only at the 4 day period at higher periods the slope wicc decorrelates rapidly along the coast but upward phase propagation implying downward propagation of energy associated with poleward propagation is evident even at these higher periods

signature of la nina in interannual variations of the east india coastal current during spring we have investigated interannual variations of the spring february april average east india coastal current eicc magnitude between 2000 and 2018 using oscar ocean surface current analysis real time current and a linear continuously stratified lcs model interannual variability of the eicc shows significant decrease in magnitude during spring of 2000 2008 and 2011 the years when high negative oni oceanic nino index for sea surface temperature value has been observed due to dominance of strong la nina events our lcs model also successfully simulates these interannual variability of the spring average eicc between 2000 and 2018 we carried out numerical experiments using lcs model related to local and remote forcing response on eicc dynamics of the eicc during spring are dominated by four different forcing processes local wind along east coast of india remote forcing response from the eastern and northern boundary of the bob including islands interior bob and the equatorial indian ocean eio during el nino and normal spring years strong poleward interannual eicc are due to very weak negligible order of 0 5 cm s 1 eicc from eio remote response and in phase poleward eicc formation using other three forcings however during la nina spring years weak order of 0 10 cm s 1 poleward interannual eicc are formed due to destructive interference between equatorward current order of 10 25 cm s 1 from eio forcing and in phase poleward current from other three forcings we have also found propagation of interannual upwelling downwelling favorable kelvin wave from eio via eastern and western boundary of the bob during spring in the el nino la nina years the interannual variations in the propagation of eio kelvin wave are associated with the changes in the eio zonal wind direction by climate mode like enso el nino southern oscillation

spatiotemporal structure of the east india coastal current from satellite altimetry we use a newly processed altimeter data set to present a hitherto unprecedented description of the spatiotemporal structure of the east india coastal current eicc the data set resolves timescales ranging from a few months to a few years and the high along track resolution yields the first description of the cross shore structure of the current the seasonal cycle dominates the variability but the nonannual timescales have similar energy levels all along the eicc path there are short lived intense intraseasonal bursts in contrast to the seasonal cycle the interannual and intraseasonal components are decorrelated along the coast and possible mechanisms for the decorrelation discontinuity in the flow are discussed in the cross shore direction the current is highly correlated at all timescales the eicc is trapped against the shelf with the current offshore flowing in the opposite direction at most locations the eicc appears as an inherently discontinuous flow taking the form of a few recirculating loops along the eicc path with a typical cross shore spatial scale of 150 200 km the loops are highly variable in direction at all timescales from intraseasonal to interannual this discontinuity of the eicc in space and time implies that the basic pathways and advective timescales for the interbasin exchange of water masses between the bay of bengal and the arabian sea are not robust when the full spatiotemporal variability of the eicc is considered

quantitative multiproxy assessment of long term patterns of holocene environmental change from a small lake near abisko northern sweden quantitative reconstructions are made of holocene changes in climatic and environmental conditions from analyses of pollen chironomids and diatoms in identical stratigraphic levels of a sediment c

origins and dynamics of the 90 day and 30 60 day variations in the equatorial indian ocean abstract sea level observations in the equatorial indian ocean show a dominant spectral peak at 90 days and secondary peaks at 30 60 days over an intraseasonal period 20 90 days a detailed investigation of the origins and dynamics of these variations is carried out using an ocean general circulation model namely the hybrid coordinate ocean model hycom two parallel experiments are performed in the tropical indian ocean basin for the period 1988 2001 one is forced by ncep 3 day mean forcing fields together with the climate prediction center cpc merged analysis of precipitation cmap pentad precipitation and the other is forced by monthly mean fields to help to understand the role played by the wind driven equatorial wave dynamics a linear continuously stratified ocean model is also used both the observed and modeled 90 day sea level anomaly fields and hycom surface current clearly show equatorial kelvin and first meridional mode rossby wave structures that are forced by the 90 day winds the

intraseasonal responses of sea surface and deep oceanic temperature anomalies in the northern indian ocean western pacific to the 30 60 day boreal summer atmospheric intraseasonal oscillation the 30 60 day boreal summer atmospheric intraseasonal oscillation bsiso is the predominant intraseasonal variability of the asian summer monsoon and has a strong dynamical and thermodynamical impact on the underlying oceans in the northern indian ocean western pacific this study uses composite analysis of satellite observed sea surface temperature sst data as well as atmospheric and oceanic reanalysis datasets for the period 1998 2013 to identify the intraseasonal behavior of sst and deep ocean temperatures during the life cycle of the bsiso with the bsiso as an organized entity evolving both eastward and northward from the equatorial indian ocean the bsiso induced sst anomalies propagate coherently into several basins including the arabian sea bay of bengal south china sea and western pacific characterized by the alternate occurrence of basin wide positive and negative sst anomalies which primarily respond to the active and suppressed convection phases of the bsiso due to anomalous southwesterlies and northeasterlies together with the resultant surface heating anomalies significant bsiso induced oceanic temperature anomalies occur in the equatorial indian ocean and western pacific with the largest amplitude anomalous signals arising around the thermocline and extending downward into the deep ocean to below 1000 m or more which are associated with the equatorial eastward propagating oceanic kelvin waves forced by anomalous surface wind stress however the local and remote effects of such equatorial oceanic kelvin waves on the sst and deep oceanic temperature anomalies especially north of the equator differ from different basins through the consequential coastal kelvin waves and reflected rossby waves

intraseasonal response of the northern indian ocean coastal waveguide to the madden julian oscillation a new observational record of upper ocean currents at 15 n on the western coast of india is dominated by intraseasonal 55 110 day variations of alongshore currents whereas sea level at the same location has a clear seasonal signal these observations can be interpreted within the framework of linear wave theory at 15 n the minimum period for planetary waves is 90 day meaning that intraseasonal energy is largely trapped at the coast in the form of poleward propagating kelvin waves while lower frequency signals associated with the annual cycle can radiate offshore as planetary waves this dynamical difference results in a steeper offshore slope of sea level at intraseasonal timescale and thus stronger geostrophic alongshore currents a consequence is that the alongshore currents are in phase with intraseasonally filtered sea level near the coast and a gridded satellite product is shown to reproduce the current variations reasonably well the intraseasonal current variations along the west coast of india are part of basin scale sea level fluctuations of the northern indian ocean equatorial and coastal waveguides the wind forcing associated with this basin scale circulation closely matches surface wind signals associated with the madden julian oscillation copyright 2009 by the american geophysical union

origins of wind driven intraseasonal sea level variations in the north indian ocean coastal waveguide 1 in this paper we show that a linear continuously stratified ocean model reproduces observed wind driven intraseasonal sea level variability in the coastal waveguide of the northern indian ocean nio sensitivity experiments with intraseasonal wind forcing selectively applied in the equatorial region bay of bengal and arabian sea show that a large part of the basin scale sea level variations are driven by zonal wind fluctuations along the equator within the nio coastal waveguide the contribution of remote equatorial forcing decreases from 80 90 in the andaman sea to 50 northeast of sri lanka and then increases to 60 70 along the west coast of india during the southwest monsoon intraseasonal wind variations become stronger over the nio resulting in a larger contribution of local wind forcing to sea level variability along the west up to 60 and east up to 40 coasts of india

intraseasonal variability in the upper layer currents observed in the eastern equatorial indian ocean 1 direct observations of the upper ocean velocity in the eastern equatorial indian ocean by an acoustic doppler current profiler from november 2000 to october 2001 on the equator at 90 e demonstrate that the dominant periods of variability in the upper layer zonal and meridional currents are in intraseasonal frequency bands with periods of 30 to 50 days and 10 to 20 days respectively the strong intraseasonal variability in the zonal current obscures the semiannual wyrtki jets which can be seen clearly in the monthly averaged field in addition a zone of strong vertical shear of the zonal current and a distinct equatorial undercurrent with semiannual period are observed the results provide us with a new perspective on importance of the energetic intraseasonal variability in the eastern equatorial indian ocean which indicates strong correlation with the wind variability near the mooring location

intraseasonal to semiannual variability of sea surface height in the astern equatorial indian ocean and southern bay of bengal intraseasonal to semiannual variability of sea surface height ssh in the eastern equatorial indian ocean eeio and southern bay of bengal bob is investigated using altimetric data and solutions to 1 layer first baroclinic mode and linear continuously stratified lcs multi baroclinic mode models the amplitude and dominant period of ssh variability differ regionally large amplitude variability is found along the west coast of sumatra in a zonal band across the bob centered along 5 n east of sri lanka and in the northwestern bob respectively along the sumatran west coast ssh variability peaks at 30 60 days 90 days and 180 days along 5 n and east of sri lanka the 30 60 day variability is dominant sensitivity experiments using a nonlinear version of the 1 layer model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern bob at 30 60 days the solutions show that eddies nonlinear rossby waves propagating from the east rather than local wind forcing account for most of the variance east of sri lanka furthermore they demonstrate that the variance is significantly enhanced by the nonlinear transfer of 90 120 day energy into the intraseasonal band of 30 60 days the lcs solutions show that the first two baroclinic modes explain most of the ssh variance at 90 180 days the second baroclinic mode dominates the ssh variance at 180 days a consequence of basin resonance and strong wind forcing

basin resonances in the equatorial indian ocean abstractprevious studies have investigated how second baroclinic mode n 2 kelvin and rossby waves in the equatorial indian ocean io interact to form basin resonances at the semiannual 180 day and 90 day periods this paper examines unresolved issues about these resonances including the reason the 90 day resonance is concentrated in the eastern ocean the time scale for their establishment and the impact of complex basin geometry a hierarchy of ocean models is used an idealized one dimensional 1d model a linear continuously stratified ocean model lcsm and an ocean general circulation model ogcm forced by quick scatterometer quikscat wind during 2000 08 results indicate that the eastern basin concentration of the 90 day resonance happens because the westward propagating rossby wave is slower and thus is damped more than the eastward propagating kelvin wave results also indicate that superposition with other baroclinic modes further enhances the eastern maximum and weakens sea level

on the physical interpretation of the lead relation between warm water volume and the el nino southern oscillation the warm water volume wwv a proxy for the equatorial pacific heat content is the most widely used oceanic precursor of the el nino southern oscillation enso the standard interpretation of this lead relation in the context of the recharge oscillator theory is that anomalous easterlies during e g la nina favour a slow recharge of the equatorial band that will later favour a transition to el nino here we demonstrate that wwv only works as the best enso predictor during boreal spring i e during enso onset in both observations and cmip5 models at longer lead times the heat content in the western pacific wwvw is the best enso predictor as initially formulated in the recharge oscillator theory using idealised and realistic experiments with a linear continuously stratified ocean model and a comprehensive wave decomposition method we demonstrate that spring wwv mostly reflects the fast kelvin wave response to wind anomalies early in the year rather than the longer term influence of winds during the previous year wwv is hence not an adequate index of the slow recharge invoked in the recharge oscillator the wwvw evolution before spring is dominated by forced rossby waves with a smaller contribution from the western boundary reflection wwvw can be approximated from the integral of equatorial wind stress over the previous 10 months thus involving a longer term time scale than wwv main time scale 3 months we hence recommend using wwvw rather than wwv as an index for the slow recharge before the spring predictability barrier

intraseasonal variability of sea surface height in the bay of bengal intraseasonal variability isv of sea surface height ssh over the bay of bengal bob is studied using altimetry data and an eddy resolving ocean model in both the model hindcast and satellite observations large ssh isv is found along the eastern and northern coasts of the bob in the western bob and in a zonal band across the bay centered near 5 degrees n the isv displays a clear seasonality in the western bob it reaches its annual maximum in spring whereas it does so in summer and autumn southeast of sri lanka driven by equatorial intraseasonal winds equatorial kelvin waves propagate eastward reach the western coast of sumatra and reflect there to propagate around the perimeter of the bob as coastally trapped waves two distinct bands of high eddy activity are detected in the western and central bob respectively in both bands isolated eddies propagate southwestward eddy formation in the eddy train in the central bay is linked to the coastal wave as it bends around the corner of the irrawaddy delta off myanmar eddy activity contributes to the high isv in the central bay to some extent an energetics analysis indicates that high total eddy energy in the western bob is due to barotropic baroclinic instability of the mean current citation cheng x s p xie j p mccreary y qi and y du 2013 intraseasonal variability of sea surface height in the bay of bengal j geophys res oceans 118 816 830 doi 10 1002 jgrc 20075

dynamics of wind forced intraseasonal zonal current variations in the equatorial indian ocean 1 this study examines the structure and dynamics of wind forced intraseasonal zonal current variability in the equatorial indian ocean we take advantage of a variety of satellite and in situ data sets including unprecedented 4 8 year long velocity time series records from the research moored array for african asian australian monsoon analysis and prediction rama program spectral analysis reveals prominent intraseasonal zonal currents variations along the equator with periods of 30 70 days these oscillations are vertically in phase above the thermocline and propagate eastward with the local zonal winds in the thermocline intraseasonal zonal velocity variations also propagate eastward across a broad range of phase speeds expected for low baroclinic equatorial kelvin waves amplitudes decrease with depth with deeper levels leading those near surface collectively these results suggest that the near surface layer responds directly to intraseasonal zonal wind stress forcing and that subsequently energy radiates downward and eastward in the thermocline in the form of wind forced equatorial kelvin waves in addition intraseasonal zonal current variability on the equator is coherent with off equatorial sea surface height fluctuations in the eastern and central of the basin this coherence is primarily due to the fact that equatorial zonal wind variations are associated with off equatorial wind stress curls that can generate local ekman pumping and westward propagating rossby waves

observational evidence for remote forcing of the west india coastal current 1 circulation in the north indian ocean is influenced by both local and remote wind forcing so far however determining the contribution of these two forcing mechanisms at a location has been possible only in numerical experiments here we separate remote and local forcing in observations using field measurements current sea level and wind for a month during march april 2003 off goa in the near coast regime of the west india coastal current wicc we show that the current was driven by local winds only at periods less than 10 days with remote forcing contributing at longer periods the high passed hp period less than 10 days component of the along shore current was strongly correlated with the hp component of the along shore wind the current lagging the wind by half a day the low passed lp components of the wind and current were not correlated the former was unidirectional but the latter reversed during the period of observation the relationship between the hp wind and current was used to estimate the locally forced lp current permitting an estimate of the remote current the lp residual this separation of locally forced and remotely forced currents showed that remote forcing contributed as much as local forcing to the wicc the local current behaved like a classical eastern boundary current forced by local winds the reversal in the remote current was due to winds 700 km farther south along the coast frictional damping had an impact only at periods less than 10 days there being no remotely forced hp current

low frequency currents from deep moorings in the southern bay of bengal abstracthigh resolution currents and hydrographic fields were measured at six deep water moorings in the southern bay of bengal bob by the naval research laboratory as part of an international effort focused on the dynamics of the indian ocean currents temperature and salinity were sampled over the upper 500 m for 20 months between december 2013 and august 2015 one of the major goals is to understand the space time scales of the currents and physical processes that contribute to the exchange of water between the bob and the arabian sea the observations captured southwest and northeast monsoon currents seasonally varying large eddies including a cyclonic eddy the sri lanka dome sld and an anticyclonic eddy southeast of the sld the observations further showed intraseasonal oscillations with periods of 30 70 days near inertial currents and tides monthly averaged velocities commonly exceeded 50 cm s 1 near the surface and extreme velocities exceeded 150 cm s 1 during the southwest monsoon ti

intraseasonal monsoon jets in the equatorial indian ocean the zonal wind in the equatorial indian ocean eqio is westerly almost throughout the year it has a strong semiannual cycle and drives the spring and fall wyrtki jets in addition high resolution daily satellite winds show westerly wind bursts lasting 10 40 days associated with atmospheric convection in the eastern eqio these bursts have the potential to produce intraseasonal eastward equatorial jets in the ocean using an ocean model driven by quikscat scatterometer winds we show that strong westerly bursts associated with summer monsoon intraseasonal oscillations can drive monsoon jets in the eastern eqio which have been observed recently although there are distinct equatorial wind bursts associated with madden julian oscillations in january march they do not produce equatorial jets in the ocean the role of ocean dynamics in producing the selective response of the ocean is discussed

vis nir reflectance of water ice regolith analogue mixtures and implications for the detectability of ice mixed within planetary regoliths permanently shadowed regions at the poles of the moon and mercury have been pointed out as candidates for hosting water ice at their surface we have measured in the laboratory the visible and near infrared spectral range vis nir bidirectional reflectance of intimate mixtures of water ice and the jsc 1af lunar simulant for different ice concentrations particle sizes and measurement geometries the nonlinearity between the measured reflectance and the amount of ice in the mixture can be reproduced to some extent by the mixing formulas of standard reflectance models in particular those of hapke and hiroi which are tested here estimating ice concentrations from reflectance data without knowledge of the mixing coefficientsstrongly dependent on the size shape of the grainscan result in large errors according to our results it is possible that considerable amounts of water ice might be intimately mixed in the regolith of the moon and mercury without producing noticeable photometric signatures