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Remote sensing-based investigation of ice flow dynamics of Polar Record glacier (PRG) during December–April of 2016-2019 has been conducted in this work. Using offset tracking method on the Sentine...

Significant changes in the interannual variation of Arctic snow and sea ice are connected to changes in the global climate. Retreat of ice sheets/glaciers is due to increased melting in many regions of the cryosphere. Active microwave sensors are frequently used to detect surface melting because of their sensitivity to the liquid water presence in snow/ice. We mapped the annual melt duration and summer melt onset for the Svalbard archipelago using microwave scatterometers flown on QuikSCAT, OSCAT, ASCAT, and OSCAT-2, providing one of the longest continuous records of radar backscatter to estimate snowmelt onset and melt duration on Svalbard spanning 2000–17. A single threshold-based model was used to detect the timing of snowmelt; the threshold was calculated using meteorological data from manned weather stations. The results capture the timing and extent of melt events caused by warm air temperature and precipitation, as a consequence of the influx of moist, mild air from the Norwegian and Barents seas. The highest melt duration and earlier melt onset occurred in southernmost and western Svalbard, in response to the influence of the warm West Spitsbergen Current. Compared to earlier studies, we found considerable interannual variability and regional differences. Though the record is short, there is an indication of an increasing trend in total days of melt duration and earlier summer melt onset date, possibly linked to the general warming trend. Climate indices such as Interdecadal Pacific Oscillation and Pacific Decadal Oscillation are well correlated with onset melt and duration across Svalbard. With the reported year-after-year decrease in sea ice cover over the Arctic Ocean, the trend toward longer snowmelt duration inferred from this study is expected to enhance the Arctic amplification.

The study explores modes of variability in the Southern Polar Cell and their relationship with known global climate modes and Antarctic sea ice. It is found that Polar Cell is barotropic in nature and 500 hPa geo-potential height (Z500) field can satisfactorily represent variability in the Polar Cell. First, three leading Empirical Orthogonal Function (EOF) modes of Z500 account for nearly 80% of observed variability in the Polar Cell. Dominant mode (PC1500) comprises of high pressure divergence zone over Antarctica. Second leading mode (PC2500) is low pressure zone covering Amundsen-Bellingshausen Sea (ABS) similar to ABS low feature. A new climate mode called Polar Coastal Index (PCI) is defined, which describes more than 15% and close to 30% variability of circumpolar trough and ABS low, respectively. Out of four modes defined in this study, only PCI and PC2500 show linear trends and clear seasonality. Interestingly, both modes are affected by modulation of ABS low due to tropical ENSO forcing. SAM signature is present in Polar Cell as PC1500 shares large variance with it. The largest impact on sea ice comes from PC2500 followed by PC1500 in the Antarctic Dipole regions. However, this study suggests contemporary sea ice trends cannot be sustained, and can reverse given that trends in PCI and PC2500 favour a reversal. These results indicate that ENSO-driven Polar Cell variability plays a crucial role influencing Antarctic sea ice as it interacts with other climate modes and leads the combined impact at the interannual time scale.

Anthropogenic warming of near-surface atmosphere in the last 50 years is dominant over the west Antarctic Peninsula. Ozone depletion has led to partly cooling of the stratosphere. The positive polarity of the Southern Hemisphere Annular Mode (SAM) index and its enhancement over the past 50 years have intensified the westerlies over the Southern Ocean, and induced warming of Antarctic Peninsula. Dictated by local ocean-atmosphere processes and remote forcing, the Antarctic sea ice extent is increasing, contrary to climate model predictions for the 21st century, and this increase has strong regional and seasonal signatures. Models incorporating doubling of present day CO2 predict warming of the Antarctic sea ice zone, a reduction in sea ice cover, and warming of the Antarctic Plateau, accompanied by increased snowfall.

High density CTD and XBT sections were covered from 35° to 56°S along 45°E and 57°30′E to investigate the morphology of the main fronts in the southwest Indian Ocean, as a part of the Indian pilot expedition to the Southern Ocean on board ORV Sagar Kanya. Northern branch of the Subtropical Front (NSTF) was observed at ∼ 35°30′S along 45°E. Along 57°30′E, the signature of the Agulhas Return Front (ARF) + Subtropical Front (STF) was identified with a rapid decrease in surface temperature between 43°30′ and 45°S and it is located with a southward shift compared to that at 45°E. The Subantarctic Front (SAF) was distinguished as two fronts as northern SAF (SAF1) and southern SAF (SAF2) along both the meridional sections. Polar Front1 (PF1) was identified between 49° and 50°S whereas Polar Front2 (PF2) was identified between 52° and 54°S along 45°E. This study reveals a southward shift of the oceanic fronts (ARF + STF) from west to east, with a maximum southward displacement of > 2° latitude at 57°30′E. A novel finding of this study is that along 45°E, SAF1 merged with ARF and SSTF and SAF2 ∼ 4° latitude southwards from the merged fronts whereas along 57°30′E, SAF1 was not identified as a merged front with ARF and STF as opposed to earlier studies [Belkin, I.M., Gordon, A.L., 1996. Southern Ocean fronts from the Greenwich Meridian to Tasmania. Journal of Geophysical Research 101, 3675–3696]. The thermocline region was absent south of PF. An enhancement in the mixed layer thickness from 42° to 52°S occurred in association with the strengthening of the wind forcing. Major water masses like Subtropical Surface Water, Subantarctic Surface Water, Mode Water, Antarctic Intermediate Water, Circumpolar Deep Water and Antarctic Bottom Water were identified along 45°E. Upper-ocean heat-content computation revealed a remarkable drop of 989 × 107 J m−2 at ∼ 42°S and 1405 × 107 J m−2 at ∼ 44°S along 45° and 57°30′E, respectively. We believe that this sudden drop in heat content affects the meridional heat transfer which is crucial to the regional climatic variability.

Using QuikScat-based vector wind data for 1999–2003, surface wind stress and turbulent heat (Q) have been mapped for the tropical Indian Ocean (IO) to understand their seasonal variability. During July wind stress is enhanced by ∼ 70% in the Arabian Sea compared to that during January. The Arabian Sea experiences a large Q loss (150–200 W/m2) during the summer and winter monsoons, which is nearly 1.3 times of that in the Bay of Bengal. The southeasterlies are strengthened during the southern hemisphere winter. Empirical Orthogonal Function analysis captures different phases of monsoon-induced variability in wind stress and Q, ranging from seasonal to high-frequency perturbations. Coherency between time coefficients of EOF-1 for wind stress and Q suggests that former leads the latter with a temporal lag of 20–40 days for period > 322 days. At high frequencies (< 21 days) Q leads wind stress with a temporal lag of 2 days. Possible explanation for wind stress leading Q over an annual time scale is offered based on the marine atmospheric boundary layer physics and pre-conditioned ocean surface, while on shorter time scales (21 days) ocean thermodynamics through mixed layer processes cause Q to lead wind stress.

Large-scale surface atmospheric convergence and divergence patterns in the Indian Ocean are mapped using high-spatial resolution, merged scatterometer wind vectors during 1991–2000. The convergence zone evolves to north of 15°S as a result of convection promoted by warm (> 28 °C) equatorial sea surface temperature (SST), and it exhibits strong intensity during boreal summer and winter. A divergence zone evolves to the south of 15°S as a result of subdued convection caused by colder SST (

Sea surface temperature (SST) patterns along the west India shelf, extending from 8° to 24°N, are analyzed during 1993–1996 to characterize seasonal variability using the advanced very high-resolution radiometer (AVHRR) SST, momentum and heat fluxes derived from ERS-1 winds and NCEP/NCAR reanalysis data. During winter monsoon (December–March), a 4-year mean SST spatial pattern shows a strong cooling north of 15°N due to surface heat depletion, while warm SSTs evolve in the south due to the intrusion of warm equatorial water. Cold water occupies the entire shelf during summer monsoon, with high degree of SST cooling dominating the Kerala coast, where Ekman pumping and upwelling promoted by the dominant alongshore wind stress component overwhelms the surface heat loss. The spectral analysis reveals semiannual and annual peaks in SST and forcing functions, which highlight the influence of monsoon forcing on the SST variability along the west India shelf.

The northern Arabian Sea is a semienclosed sea with high primary productivity and a complicated flow pattern consisting of several eddies. This paper reports on phytoplankton blooms, which were associated with a cold eddy in the northern Arabian Sea during November 1996, inferred from Ocean Color and Temperature Scanner (OCTS) and Sea-view Wide Field-of-view Sensor (SeaWiFS)-derived chlorophyll a (Chl-a hereafter), AVHRR sea surface temperature (SST), and other available oceanography data. The blooms emerged at 100 km from both coasts in the Gulf of Oman (60.5°E, 24.5°N) where the depth is about 3000 m. The Chl-a concentrations patch first appeared on November 2 and decayed after about 4 weeks (December 3, 1996). The high Chl-a concentrations patch was about 100 km in diameter and it was located at 60.3–61.3°E, 23.5–24.5°N. The bloom, having a mean Chl-a concentration of 6.8 mg m−3 on November 6, was located in a cold SST eddy, which was accompanied by another feature, an anticyclone eddy (of 100 km in diameter) with high SST and low Chl-a concentrations to the southwest (61.5°E, 22.5°N). An SST drop occurred around November 14, which coincides with a peak of the vertical pumping velocity derived from NSCAT-derived wind stress. Two SeaWiFS-derived Chl-a images obtained in November 1998 and 1999 show good agreement in terms of the locations and features with those described above through the OCTS observations. The possible mechanism for this newly identified Chl-a patch is discussed.

This work addresses the analysis of winter monsoon forcing and sea surface temperature (SST) cooling events in the Gulf of Mannar, which is situated between the southeast of the Indian tip and northwest of Sri Lanka, using a 7-year data set derived from satellite sensors. The surface forcing consists of wind stress and turbulent heat flux, which were estimated through the TOGA/COARE algorithm using Special Sensor Microwave Imager (SSM/I) wind, Advanced Very High Resolution Radiometer (AVHRR) SST, and surface atmospheric conditions derived from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses data. Net heat flux was derived by combining the turbulent heat flux with net short- and long-wave radiation from the NCEP/NCAR reanalysis data set. SST cooling was monitored by using 9-km spatial resolution pathfinder SST that was derived from the AVHRR. The 7-year weekly mean maps of wind stress, net heat flux, and SST indicate that SST cooling is locally influenced by surface forcing in- and offshore of the Gulf of Mannar. A time series of these parameters near the Indian tip reveal that the strong wind stress and high surface heat loss, which are punctuated in time varying from 15 days to more than a month, occur every winter and lower SST by ∼1.5°C. The occurrence of such a phenomenon is referred to as an event in this work. The bell-shaped events, which have a periodicity of 15 days with a maximum wind stress around Day 8, occur every winter and are characterized by the SST cooling of less than a degree. The features of these events are studied by using the statistical correlation and composite technique. It is inferred that the SST cooling is strongly correlated with the surface forcing.

Upper layer (0}400 m) geostrophic volume transport associated with the major current systems of the tropical Indian Ocean along the near-meridional TOGA-India XBT tracklines from Mumbai to Mauritius during 1992}1996 is discussed. The transport of the eastward #owing Indian Monsoon Current (IMC) varies between 9 and 14 Sv (1 Sv"106 m3 s~1) during southwest monsoon. The westward #owing North Equatorial Current (NEC) transports about 8 Sv during boreal winter. The westward #owing south equatorial current (SEC) has its lowest transport (10}12 Sv) during austral fall and spring and highest transport (18}21 Sv) during austral winter and summer. The northern boundary of the SEC extends equatorward as far north as for 4}53S during southwest monsoon from its usual location of 8}103S. The eastward #owing South Equatorial Counter Current (SECC) exhibits highest transport (37 Sv) during peak austral summer (January) and between 5 and 20 Sv during the rest of the year. In March and May, eastward undercurrents are noticed near the equator. In June and July, the undercurrents are present south of Sri Lanka away from the equator. The equatorial #ow in the zonal belts 1}23N and 1}23S exhibits westward transport of 6}20 Sv during January}February. This broad westward #ow and the SECC constitute an anticlockwise equatorial gyre during boreal winter. In addition to the above current systems, signatures of a warm-core anticyclonic eddy centered at 83N, 72.53E and a cold-core cyclonic eddy centered at 10.53N, 72.53E are also noticed in February and October, respectively, o! the southwest coast of India. The volume transport associated with the warm-core eddy is about 10 Sv directed equatorward and that with the cold-core eddy is 2.5 Sv directed poleward. ( 2000 Elsevier Science Ltd. All rights reserved.

This report addresses a case of topographic air–sea interaction in the Gulf of Mannar, near the Indian tip, for the winter monsoon of 1996–1997. Using high spatial resolution NASA-Scatterometer (NSCAT) wind data, a 1°×1° region of strong wind is identified in the Gulf during the peak of the winter monsoon. The characteristic topography of South India and Sri Lanka and their orientation to the monsoon wind tend to channel this strong wind. Air–sea heat flux analyses, using the NSCAT wind and the European Center for Medium-Range Weather Forecast objective analyses surface data, reveal that the strong winter monsoon bursts cause large latent heat loss (180 W/m2) from a wind-fetch region centered on 7.5°N, 77.5°E during January. Weak air–sea temperature gradients result in weak sensible heat loss (

[1] Topographic meandering of Antarctic Circumpolar Current (ACC) is found to be an impediment in the propagation of Antarctic Circumpolar Wave (ACW) in the Indian Ocean sector of Antarctica. Reasons for this are attributed to the southward advection of the ACW anomalies associated with the topographic meandering of the ACC. The southward meandering of ACC facilitates warming up of the region east of 20°E by about 1°C during winter, thereby reducing the sea ice; these processes interfere with the eastward propagating positive sea‐ice anomalies, and reduce its strength. Warming of ocean induced by topographic meandering leads to upward vertical velocities between 40°–60°E, where the ocean surface velocities are weak and southward, and the vertical/meridional advection of temperature dominates the zonal advection in the atmosphere. This results in the decoupling of the ACW in the region east of 40°E. In regions out side the Indian Ocean sector, vertical advection is minimum and zonal velocity of ACC becomes positive, which facilitates the ACW propagation in the Central Pacific, Ross and Weddell Seas. Citation: Nuncio, M., A. J. Luis, and X. Yuan (2011), Topographic meandering of Antarctic Circumpolar Current and Antarctic Circumpolar Wave in the ice‐ ocean‐atmosphere system, Geophys. Res. Lett., 38, L13708

[1] Seasonal variability of surface wind stress derived from SeaWINDS onboard the NASA's QuikSCAT satellite is mapped over the latitude range 30°–60°S in the Southern Ocean for the period from August 1999 to July 2003. Seasonal variability is pronounced on basin-wide scale which dominates the Atlantic-Indian Ocean sector during austral winter. Harmonic analysis reveals that seasonal harmonic captures larger than 60% of the variance on regional scales. The cyclonic wind stress curl induces divergence around Antarctica and facilitates ACC meandering equatorward in the Atlantic-Indian Ocean sector of the Southern Ocean.

Atmospheric convergence regions over the tropical Indian Ocean have been mapped for the first time using 31 years of vector wind data. The convergence fields reveal that the energetic summer monsoon winds enhance convergence in the central Arabian Sea and in the eastern Bay of Bengal when compared with weak winter monsoon winds. The summer monsoon is also effective in spatial migration of convergence regions in both basins. Area-integrated convergence time series reveals an annual cycle with high amplitude during summer monsoon, which occurs in phase with Indian rainfall. The study explores the prospects of using the convergence as one of the predictors of Indian rainfall.

[1] We report on sea surface temperature (SST) cooling in the Gulf of Oman during winter monsoon 1993 using evidence from the advanced very high resolution radiometer (AVHRR). A combination of the AVHRR SST and scatterometer-based momentum and heat fluxes is used to discuss the SST-cooling mechanism. Cold SST evolves in the gulf during an intense outbreak of wintertime winds. The turbulence generated by these winds in the surface atmospheric boundary layer depletes large heat from the sea surface and cause 1–2°C SST cooling during January–March. Additionally, the alongshore component of the wind stress promotes Ekman dynamics and further enhances SST cooling along the periphery of the gulf.

[1] Wintertime sea surface temperature (SST) cooling south of the Indian tip (hereafter tip) is investigated during a 14 day gap wind event (21 January to 3 February 1997) using satellite data and the three-dimensional, primitive equation, sigma coordinate Princeton Ocean Model (POM). The advanced very high resolution radiometer SST reveals surface cooling of 1.5°C over the 14 day period near west of Sri Lanka. A spatial-mean time series of surface forcing west of Sri Lanka indicate a bell-shaped pattern, which is characterized by maximum wind stress and outgoing heat flux (sum of turbulent heat flux and net surface long-wave radiation) of 0.12 N/m2 and 450 W/m2, respectively, on 27 January. POM simulation is performed with realistic bottom topography, with seasonal stratification, and with daily mean surface forcing derived from NASA scatterometer (NSCAT) winds and National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) meteorological variables. During 21–28 January, Ekman dynamics together with positive wind stress curl promote SST cooling along the west coast of Sri Lanka. Thereafter irregular and shallow topography near the tip promotes diapycnal mixing, and the characteristic surface circulation significantly influences the evolution of the SST pattern along the periphery of the tip. An anticyclonic circulation evolves in the Gulf of Mannar under the influence of local negative wind stress curl after 27 January. Examination of a zonal section of density and vertical heat diffusion reveals that the initial stratification in the vicinity of the tip weakens because of diapycnal mixing and vertical diffusion of the surface heat. The mixed layer heat budget near the west of Sri Lanka and south of the tip reveals that the surface heat depletion dictates SST changes throughout the event. From our earlier works [Luis and Kawamura, 2000, 2001] and from the results of the present investigation it is inferred that the wintertime SST cooling in the vicinity of the tip is a case of topography-monsoon-ocean interaction.

This paper addresses analysis of surface meteorological and hydrographic data collected along the transects Durban–India Bay, Antarctica (Track-1) and Prydz Bay–Mauritius (Track-2) during February–March 2007 as part of the International Polar Year project (IPY#70). Strong winds (>12 m s−1) resulted in enhanced turbulent heat loss north of 45°S. Whereas a highly stable marine atmospheric boundary layer (MABL) and strong winds facilitated the release of latent heat of condensation along Track-1, a highly unstable MABL and strong winds resulted in large turbulent heat loss from the sea surface along Track-2, in the 40–45°S belt. The northern and southern branches of Subantarctic Front on both tracks coalesce, while the Agulhas Retroflection Front (AF) and South Subtropical Front (SSTF) merge between 43° and 44°S on Track-2. The southern branch of the Polar Front (PF2) meanders 550 km southward towards the east. The Subtropical Surface Water, Central Water, and Mode Water are located north of 43.5°S, while the Subantarctic Surface Water, Antarctic Surface Water, Antarctic Intermediate Water, and Circumpolar Deep Water are encountered in the region of the Antarctic Circumpolar Current (ACC). Baroclinic transport relative to 1000 db reveals that the ACC is enhanced by 10 × 106 m3 s−1 eastward, and a four-fold increase in transport occurs south of the ACC. Nearly 50% of the ACC transport occurs in the 100–500 m slab. We discuss the effects of the feedback of AC and hydrological fronts on the MABL.