Anna I. Ginzburg

Mesoscale eddies and related processes in the northeastern Black Sea

Abstract Mesoscale dynamics in the northeastern Black Sea in Autumn 1993 and 1997 is considered on the basis of analysis of the NOAA AVHRR imagery together with relevant hydrographic measurements and meteorological information. Over the course from 6 September to 8 October 1997, five near-shore anticyclonic eddies (NAEs) about 40 km in diameter were observed within the region between Tuapse and the Kerch Strait, their movement speed reaching about 15 cm/s at separate parts of their trajectories. Separation of an NAE (NAE-1) from the coast in the region of a widening shelf/slope west of Novorossiysk and its transformation into deep-sea eddy was traced. Lifetime of the anticyclone was no less than 1 month, its mean offshore speed was about 4.3 cm/s. According to the SeaWiFS data, the increased chlorophyll a concentration (compared with the mean concentration at the center of the eastern part of the sea) was observed on 8 October 1997 in four “young” NAEs after an intense precipitation, the decreased one at the same time occurred in NAE-1, which was depleted of supply by shelf waters. In Summer 1993, a large NAE (about 95 km in diameter) was observed in the region between Tuapse and Gelendzhik. Evolution of the eddy from 3 June to 8 November 1993 was traced. Lifetime of the eddy exceeded 5 months. Its mean offshore speed to the southwest since its separation from the coast (around 17 August) in the Novorossiysk region was about 1.2 cm/s. The difference between dynamic situations in the same season (autumn) of 2 years, 1997 and 1993, was likely associated with peculiarities of atmospheric circulation and related intensity of cyclonic circulation in the Black Sea.

Oceanic eddies in synthetic aperture radar images

Continuous observations since 1991 by using synthetic aperture radar (SAR) on board the Almaz1, ERS-1/2, JERS-1, and RADARSAT satellites support the well-known fact that oceanic eddies are distributed worldwide in the ocean. The paper is devoted to an evaluation of the potential of SAR for detection of eddies and vortical motions in the ocean. The classification of typical vortical features in the ocean detected in remote sensing images (visible, infrared, and SAR) is presented as well as available information on their spatial and temporal scales. Examples of the Almaz-1 and ERS-1/2 SAR images showing different eddy types, such as rings, spiral eddies of the open ocean, eddies behind islands and in bays, spin-off eddies and mushroom-like structures (vortex dipoles) are given and discussed. It is shown that a common feature for most of the eddies detected in the SAR images is a broad spectrum of spatial scales, spiral shape and shear nature. It is concluded that the spaceborne SARs give valuable information on ocean eddies, especially in combination with visible and infrared satellite data.

Exploiting satellite altimetry in coastal ocean through the ALTICORE project

Altimeter-derived information on sea level and sea state could be extremely important for resolving the complex dynamics of the coastal ocean. Satellite altimetry was not originally conceived with coastal ocean in mind, but future missions (AltiKa and CryoSat-2) promise much improved nearshore capabilities. A current priority is to analyze the existing, under-exploited, 15-year global archive of coastal altimeter data to draw recommendations for these missions. There are intrinsic difficulties in processing and interpretation of the data, e.g.: the proximity of land, control by the seabed, and rapid variations due to tides and atmospheric effects. But there are also unexploited possibilities, including higher along track data rates and multi-altimetry scenarios that need to be explored. There are also difficulties of accessing and manipulating data from multiple sources, many of which undergo regular revision and enhancement. In response to these needs, the ALTICORE (ALTImetry for COastal REgions - www.alticore.eu) project started in December 2006, funded for two-years by the European INTAS scheme (www.intas.be). The overall aim of ALTICORE is to build up capacity for provision of altimeter-based information in support of coastal ocean studies in some European Seas (Mediterranean, Black, Caspian, White and Barents). ALTICORE will also contribute to improved cooperation between Europe and Eastern countries and enhance networking of capacity in the area of satellite altimetry. This paper discusses the approach, summarizes the planned work and shows how the coastal community should eventually benefit from better access to improved altimeter-derived information.

Thermal regime of the Aral Sea in the modern period (1982–2000) as revealed by satellite data

Abstract A weekly mean Multi-Channel Sea Surface Temperature (MCSST) data set based on NOAA satellite measurements (spatial and temperature resolution of about 18 km and 0.1 °C) was used to reveal the changes of SST of the Aral Sea and of its individual regions during the modern anthropogenic period (1982–2000). By a joint analysis of satellite SST and in situ measurements in the 1950s, it was found that by 2000, with water level lowering by 19 m as compared with the conventionally natural period (prior to 1960), the monthly mean SSTs in August and May increased by 2–2.5 and 4–5 °C, respectively, whereas in November, the temperature decreased by 1.5–2.5 °C. A shift of the spring and autumn temperature phases (by a month and half month, respectively) occurred in the direction of their earlier onset. Because of increasing mean-August SSTs (higher than 25.5 °C) and decreasing winter SSTs, the seasonal temperature amplitude exceeded 27 °C (in the 1950s, it was 24 °C). Since 1995, a decrease of the annual mean SST has been observed (to 11.7 °C by 2000). On the whole, the results support the predictions made in the 1950s concerning the upcoming changes of the Aral Sea thermal state associated with its desiccation, except for some increases of the annual mean SSTs between 1980s and the mid-1990s.

Vortex dynamics in the southeastern Baltic Sea from satellite radar data

The analysis of radar satellite images shows that vortex dipoles are a typical element of the water circulation in the southeastern part of the Baltic Sea. The wide range of spatial dimensions of observed vortices (from approximately 2 to 25 km) corresponds to mesoscale and submesoscale vortex formations (signifying whether the diameter is respectively larger or smaller than the baroclinic Rossby radius of deformation, equal to 5–6 km). Vortex dipoles typical for different areas and their spatial characteristics are considered. These areas were the Hel Spit, the Taran Cape, the central part of the Gulf of Gdañsk and the area northward of the Gulf. It is shown that the mesoscale vortex dipoles and the associated jets condition horizontal water exchange in an area comparable with the size of the considered water area. The differences in the appearance of the cyclonic and anticyclonic components of vortex dipoles revealed in satellite radar images are discussed.

Satellite Altimetry Applications in the Barents and White Seas

The Barents and White Seas are the seas of the Arctic Ocean. Today complicated hydrodynamic, tidal, ice, and meteorological regimes of these seas may be investigated on the basis of remote sensing data, specifically of satellite altimetry data. Results of calibration and validation of satellite altimetry measurements (sea surface height and sea surface wind speed) and comparison with regional tidal model show that this type of data may be successfully used in scientific research and in monitoring of the environment. Complex analysis of the tidal regime of the Barents and White Seas and comparison between global and regional tidal models show advantages of regional tidal model for use in tidal correction of satellite altimetry data. Examples of using the sea level data in studying long-term variability of the Barents and White Seas are presented. Interannual variability of sea ice edge position is estimated on the basis of altimetry data.

Satellite Altimetry Applications in the Black Sea

Physical processes in the coastal zone of the Black Sea which can contribute to a correlation between altimeter-derived SLA (sea level anomaly) data and corresponding in situ measurements are briefly reviewed. Examples of using the SLA data in studying long-term variability of the Black Sea level and mesoscale water dynamics are presented. Results of comparison between observed (in situ) and altimeter-derived SLA and wind speed values made for several coastal locations are discussed. A new approach is proposed for better consistency between altimeter-derived and observed wind speed values, which is on the basis of the decomposition of the wind directions in four quadrants in relation to the coastline orientation.

Reprocessing Altimeter Data Records along European Coasts: Lessons Learned from the Alticore Project

A coastal-oriented processing strategy has been developed in the Northwestern part of the Mediterranean Sea and has showed that improved altimetry in the coastal ocean is feasible and could be extended to other regions. In this work, we will provide an overview of current capabilities and challenges of existing altimetry products in Black, Caspian, White and Barents seas, in the prospect of increasing the quantity and quality of data in these regions. With respect to the work done in the project called ALTICORE (ALTImetry for COastal REgions - www.alticore.eu), the obstacles limiting the use of the data and the possible areas of improvement are highlighted and discussed.

ALTICORE - A consortium serving european seas with coastal altimetry

In this paper, we describe the ALTICORE (value added satellite ALTImetry in COastal REgions) initiative, a consortium aiming at providing high quality coastal altimetry over some European seas. Taking the Ligurian Sea in the NW Mediterranean as an example, which acts as a test zone for this work, we show the improvement in availability and quality of ENVISAT data, through our processing, when compared with the official altimetric products delivered by AVISO. We also introduce the building concepts of solutions for data search, extraction, update and delivery based on web-services. This grid-type infrastructure is being designed within ALTICORE.

Comprehensive Satellite Monitoring of Caspian Sea Conditions

Satellite data on sea surface temperature (SST), visible and infrared imagery as well as altimetry and radar measurements were used to monitor different parameters of the Caspian Sea. Interannual variability of sea level (1993–2015) and SST (1982–2015) is considered. The elements of mesoscale water dynamics (vortices, jet-like flows, fine structure of upwelling frontal zone, internal waves, etc.) are discussed and examples of oil pollution are shown.