Combined influence of oceanic and atmospheric circulations on Greenland sea ice concentration

The amount and spatial extent of Greenland Sea (GS) ice are primarily controlled by the sea ice export across the Fram Strait (FS) and by local seasonal sea ice formation, melting, and sea ice dynamics. In this study, using satellite passive microwave sea ice observations, atmospheric and a coupled ocean-sea ice reanalysis system, TOPAZ4, we show that both the atmospheric and oceanic circulation in the Nordic Seas (NS) act in tandem to explain the SIC variability in the south-western GS. Northerly wind anomalies associated with anomalously low sea level pressure (SLP) over the NS reduce the sea ice export in the south-western GS due to westward Ekman drift of sea ice. On the other hand, the positive wind stress curl strengthens the cyclonic Greenland Sea Gyre (GSG) circulation in the central GS. An intensified GSG circulation may result in stronger Ekman divergence of surface cold and fresh waters away from the south-western GS. Both of these processes can reduce the freshwater content and weaken the upper-ocean stratification in the south-western GS. At the same time, warm and saline Atlantic Water (AW) anomalies are recirculated from the FS region to the south-western GS by a stronger GSG circulation. Under weakly stratified conditions, enhanced vertical mixing of these subsurface AW anomalies can warm the surface waters and inhibit new sea ice formation, further reducing the SIC in the south-western GS.publishedVersio

Observation of Cloud Base Height and Precipitation Characteristics at a Polar Site Ny-Ålesund, Svalbard Using Ground-Based Remote Sensing and Model Reanalysis

Clouds play a significant role in regulating the Arctic climate and water cycle due to their impacts on radiative balance through various complex feedback processes. However, there are still large discrepancies in satellite and numerical model-derived cloud datasets over the Arctic region due to a lack of observations. Here, we report observations of cloud base height (CBH) characteristics measured using a Vaisala CL51 ceilometer at Ny-Ålesund, Svalbard. The study highlights the monthly and seasonal CBH characteristics at the location. It is found that almost 40% of the lowest CBHs fall within a height range of 0.5–1 km. The second and third cloud bases that could be detected by the ceilometer are mostly concentrated below 3 km during summer but possess more vertical spread during the winter season. Thin and low-level clouds appear to be dominant during the summer. Low-level clouds are found to be dominant and observed in 76% of cases. The mid and high-level clouds occur in ~16% and ~7% of cases, respectively. Further, micro rain radar (MRR2) observed enhanced precipitation and snowfall events during the winter and spring which are found to be associated with the lowest CBHs within 2 km from the ground. The frontal process associated with synoptic-scale meteorological conditions explains the variabilities in CBH and precipitation at the observation site when compared for two contrasting winter precipitation events. The findings of the study could be useful for model evaluation of cloud precipitation relationships and satellite data validation in the Arctic environment

Propagation of tides in the Cochin estuarine system, southwest coast of India

14-24 Analysis of hourly data on sea level collected at four stations in the Cochin estuarine system has been made to understand the tidal and non-tidal sea level variations inside the estuary, for spring and neap phases during March 2000. Spring phase was dominated by semi-diurnal tides whereas neap phase was dominated by diurnal tides. Diurnal and semi-diurnal bands were together responsible for a high percentage of variance of the observed sea level. The dominance of shallow water tides was seen with increasing distance from the mouth. The sea level variance was dominated mainly by tidal signals, but the tidal influence decreased rapidly inside the estuary. Doodson’s Xo filter appears to be efficient for de-tiding the observed sea level time series. </smarttagtype

Sea level and currents in the upper reaches of the Cochin estuarine system during October 2000

155-163Data on sea level, currents, salinity and water temperature collected in the upper reaches of the Cochin estuarine system (southwest coast of India) during October 2000 have been analysed to understand their variability. The tides near to the mouth of the Cochin estuarine system were found to be of a mixed, predominantly semi-diurnal form during the month. The non-tidal sea level at the same location, showed an overall drop of nearly 9 cm during the period. Spectral analysis of the non-tidal sea level revealed the presence of 4 and 21 day period wave phenomena. The study showed that the sea level as well as currents are dominated by tidal signals (diurnal and semi-diurnal bands) even in the upper reaches. However, the amplitudes were seen to decrease with increasing distance from the mouth of the estuarine system. Conspicuous dominance of the shallow water components was noticed in the currents as compared to the sea level. The data on salinity showed tidal signatures whereas that on the water temperature showed strong solar forcing

Currents in the Cochin estuarine system [southwest coast of India] during March 2000

123-132Analysis of current meter data collected in the Cochin estuarine system (southwest coast of India) has been made, to understand variations of currents in the estuary for spring and neap tidal phases during March 2000. The currents were strongest at an interior station as compared to stations close to the mouth of the estuary. The currents were also found to be rectilinear in nature at most of the stations. The observed currents were dominated by tidal signals - spring phase was dominated by semi-diurnal and neap phase by diurnal tidal currents

Intense blooms of Trichodesmium erythraeum (Cyanophyta) in the open waters along east coast of India

Two blooms of Trichodesmium erythraeum were observed during April 2001, in the open waters of Bay of Bengal and this is the first report from this region. The locations of the bloom were off Karaikkal (10°58′N, 81°50′E) and off south of Calcutta (19° 44′N, 89° 04′), both along east coast of India. Nutrients (nitrate, phosphate, silicate) concentration in the upper 30 m of the water column showed very low values. High-integrated primary production (Bloom 1-2160 mgC m -2 d -1 , Bloom 2-1740 mgC m -2 d -1 ) was obtained in these regions, which indicated the enhancement of primary production in the earlier stages of the bloom. Very low NO 3 -N concentrations, brownish yellow bloom colour, undisturbed patches and high primary production strongly suggested that the blooms were in the growth phase. Low mesozooplankton biomass was found in both locations and was dominated by copepods followed by chaetognaths.

Intense blooms of <i>Trichodesmium erythraeum</i> (Cyanophyta) in the open waters along east coast of India

165-167Two blooms of Trichodesmium erythraeum were observed during April 2001, in the open waters of Bay of Bengal and this is the first report from this region. The locations of the bloom were off Karaikkal (10°58N, 81°50E) and off south of Calcutta (19° 44N, 89° 04), both along east coast of India. Nutrients (nitrate, phosphate, silicate) concentration in the upper 30 m of the water column showed very low values. High-integrated primary production (Bloom 1- 2160 mgC m-2 d-1, Bloom 2-1740 mgC m-2 d-1) was obtained in these regions, which indicated the enhancement of primary production in the earlier stages of the bloom. Very low NO3-N concentrations, brownish yellow bloom colour, undisturbed patches and high primary production strongly suggested that the blooms were in the growth phase. Low mesozooplankton biomass was found in both locations and was dominated by copepods followed by chaetognaths

Combined influence of oceanic and atmospheric circulations on Greenland sea ice concentration

The amount and spatial extent of Greenland Sea (GS) ice are primarily controlled by the sea ice export across the Fram Strait (FS) and by local seasonal sea ice formation, melting, and sea ice dynamics. In this study, using satellite passive microwave sea ice observations, atmospheric and a coupled ocean-sea ice reanalysis system, TOPAZ4, we show that both the atmospheric and oceanic circulation in the Nordic Seas (NS) act in tandem to explain the SIC variability in the south-western GS. Northerly wind anomalies associated with anomalously low sea level pressure (SLP) over the NS reduce the sea ice export in the south-western GS due to westward Ekman drift of sea ice. On the other hand, the positive wind stress curl strengthens the cyclonic Greenland Sea Gyre (GSG) circulation in the central GS. An intensified GSG circulation may result in stronger Ekman divergence of surface cold and fresh waters away from the south-western GS. Both of these processes can reduce the freshwater content and weaken the upper-ocean stratification in the south-western GS. At the same time, warm and saline Atlantic Water (AW) anomalies are recirculated from the FS region to the south-western GS by a stronger GSG circulation. Under weakly stratified conditions, enhanced vertical mixing of these subsurface AW anomalies can warm the surface waters and inhibit new sea ice formation, further reducing the SIC in the south-western GS