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Semyon A. Grodsky

Bio: Semyon A. Grodsky is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Sea surface temperature & Tropical Atlantic. The author has an hindex of 28, co-authored 75 publications receiving 2273 citations. Previous affiliations of Semyon A. Grodsky include National Academy of Sciences of Ukraine & University of Maryland, Baltimore.


Papers
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Journal ArticleDOI
TL;DR: In this paper, a reanalysis of the global ocean circulation is used to distinguish between the steric and eustatic components of sea level rise, and the contribution from steric effects is explored using the new eddy-permitting Simple Ocean Data Assimilation version 1.2 (SODA1.2) reanalysis.
Abstract: [1] A new reanalysis of the global ocean circulation is used to distinguish between the steric and eustatic components of sea level rise. Recent altimeter observations indicate an increase in the rate of sea level rise during the past decade to 3.2 mm/yr, well above the centennial estimate of 1.5–2 mm/yr. This apparent increase could have resulted from enhanced melting of continental ice or from decadal changes in thermosteric and halosteric effects. The contribution from steric effects is explored using the new eddy-permitting Simple Ocean Data Assimilation version 1.2 (SODA1.2) reanalysis of global temperature, salinity, and sea level spanning the period 1958–2001. The applicability of this ocean reanalysis for sea level studies is evaluated by comparing subseasonal variability with a collection of 20 tide gauge station sea level records, comprising a total of 740 years of data. A positive relationship is found at all gauge stations, with an average correlation of r = 0.7 after correction for the inverted barometer effect. Dynamic height calculated relative to 1000m from the SODA1.2 reanalysis, used as a proxy for the steric component of sea level, is compared with satellite-derived sea level for the years 1993–2001. During this 9-year period dynamic height increases at a global rate of 2.3 ± 0.8 mm yr−1, a substantial acceleration beyond the multidecadal steric rate of 0.5 mm yr−1. The similarity of the rate of increase in the thermosteric contribution to sea level rise as well as the similarity of its spatial structure in comparison with satellite-derived sea level rise suggests that the recent acceleration in sea level rise is explainable to within the error estimates by fluctuations in warming and thermal expansion of the oceans.

250 citations

Journal ArticleDOI
TL;DR: In this article, the authors analyzed the mixed layer heat balance at eight PIRATA mooring locations and found that the seasonal cycles of latent heat loss and absorbed shortwave radiation are responsible for seasonal SST variability in the northwest basin (8°N-15°N along 38°W).
Abstract: [1] This paper addresses the atmospheric and oceanic causes of the seasonal cycle of sea surface temperature (SST) in the tropical Atlantic on the basis of direct observations Data sets include up to 4 years (September 1997 to February 2002) of measurements from moored buoys of the Pilot Research Array in the Tropical Atlantic (PIRATA), near-surface drifting buoys, and a blended satellite in situ SST product We analyze the mixed layer heat balance at eight PIRATA mooring locations and find that the seasonal cycles of latent heat loss and absorbed shortwave radiation are responsible for seasonal SST variability in the northwest basin (8°N–15°N along 38°W) Along the equator (10°W–35°W), contributions from latent heat loss are diminished, while horizontal temperature advection and vertical entrainment contribute significantly Zonal temperature advection is especially important during boreal summer near the western edge of the cold tongue, while horizontal eddy temperature advection, which most likely results from tropical instability waves, opposes temperature advection by the mean flow The dominant balance in the southeast (6°S–10°S along 10°W) is similar to that in the northwest, with both latent heat loss and absorbed solar radiation playing important roles

164 citations

Journal ArticleDOI
TL;DR: In this paper, a new sea surface salinity (SSS) observations from the Aquarius/SACD and SMOS satellites help elucidate the ocean response to hurricane Katia, which crossed the plume in early fall 2011.
Abstract: [1] At its seasonal peak the Amazon/Orinoco plume covers a region of 106 km2in the western tropical Atlantic with more than 1 m of extra freshwater, creating a near-surface barrier layer (BL) that inhibits mixing and warms the sea surface temperature (SST) to >29°C. Here new sea surface salinity (SSS) observations from the Aquarius/SACD and SMOS satellites help elucidate the ocean response to hurricane Katia, which crossed the plume in early fall, 2011. Its passage left a 1.5 psu high haline wake covering >105 km2 (in its impact on density, the equivalent of a 3.5°C cooling) due to mixing of the shallow BL. Destruction of this BL apparently decreased SST cooling in the plume, and thus preserved higher SST and evaporation than outside. Combined with SST, the new satellite SSS data provide a new and better tool to monitor the plume extent and quantify tropical cyclone upper ocean responses with important implications for forecasting.

120 citations

Journal ArticleDOI
TL;DR: In this article, a methodology is applied to the data to automatically reanalyze drogue presence based on anomalous downwind ageostrophic motion, and results indicate that the downwind slip of undrogued drifters is approximately 50% higher than previously believed.
Abstract: Satellite-tracked drifting buoys of the Global Drifter Program have drogues, centered at 15-m depth, to minimize direct wind forcing and Stokes drift. Drogue presence has historically been determined from submergence or tether strain records. However, recent studies have revealed that a significant fraction of drifters believed to be drogued have actually lost their drogues, a problem that peaked in the mid-2000s before the majority of drifters in the global array switched from submergence to tether strain sensors. In this study, a methodology is applied to the data to automatically reanalyze drogue presence based on anomalous downwind ageostrophic motion. Results indicate that the downwind slip of undrogued drifters is approximately 50% higher than previously believed. The reanalyzed results no longer exhibit the dramatic and spurious interannual variations seen in the original data. These results, along with information from submergence/tether strain and transmission frequency variations, are now being used to conduct a systematic manual reevaluation of drogue presence for each drifter in the post-1992 dataset. Satellite-tracked drifting buoys (hereafter ‘‘drifters’’) of the Global Drifter Program (GDP) have been collecting near-surface ocean current observations in the tropical Pacific since 1979, with observations in the other basins also now spanning more than 15 years. The GDP is a branch of the National Oceanic and Atmospheric Administration’s (NOAA) Global Ocean Observing System and a scientific project of the Data Buoy Cooperation Panel, and is funded by NOAA’s Climate Program Office. Its objectives are to maintain a global array of ;1250 drifters and to provide a data processing system for scientific use of the resulting observations, which support short-term (seasonal to interannual) climate predictions, climate research, and climate monitoring. A subset of the driftersalso includes barometers for improved numerical weather forecasting efforts. The GDP works with a large number of national and international partners

98 citations


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01 Jun 2005

3,154 citations

Journal ArticleDOI
TL;DR: In this paper, a 2° resolution global climatology of the mixed layer depth (MLD) based on individual profiles is constructed and a new global seasonal estimation of barrier layer thickness is also provided.
Abstract: [1] A new 2° resolution global climatology of the mixed layer depth (MLD) based on individual profiles is constructed. Previous global climatologies have been based on temperature or density-gridded climatologies. The criterion selected is a threshold value of temperature or density from a near-surface value at 10 m depth (ΔT = 0.2°C or Δσθ = 0.03 kg m−3). A validation of the temperature criterion on moored time series data shows that the method is successful at following the base of the mixed layer. In particular, the first spring restratification is better captured than with a more commonly used larger criteria. In addition, we show that for a given 0.2°C criterion, the MLD estimated from averaged profiles results in a shallow bias of 25% compared to the MLD estimated from individual profiles. A new global seasonal estimation of barrier layer thickness is also provided. An interesting result is the prevalence in mid- and high-latitude winter hemispheres of vertically density-compensated layers, creating an isopycnal but not mixed layer. Consequently, we propose an optimal estimate of MLD based on both temperature and density data. An independent validation of the maximum annual MLD with oxygen data shows that this oxygen estimate may be biased in regions of Ekman pumping or strong biological activity. Significant differences are shown compared to previous climatologies. The timing of the seasonal cycle of the mixed layer is shifted earlier in the year, and the maximum MLD captures finer structures and is shallower. These results are discussed in light of the different approaches and the choice of criterion.

2,345 citations

Journal ArticleDOI
TL;DR: In this article, the authors found that anomalous warming events different from conventional El Nino events occur in the central equatorial Pacific, where a horseshoe pattern is flanked by a colder sea surface temperature anomaly (SSTA) on both sides along the equator.
Abstract: [1] Using observed data sets mainly for the period 1979–2005, we find that anomalous warming events different from conventional El Nino events occur in the central equatorial Pacific. This unique warming in the central equatorial Pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly (SSTA) on both sides along the equator. empirical orthogonal function (EOF) analysis of monthly tropical Pacific SSTA shows that these events are represented by the second mode that explains 12% of the variance. Since a majority of such events are not part of El Nino evolution, the phenomenon is named as El Nino Modoki (pseudo-El Nino) (“Modoki” is a classical Japanese word, which means “a similar but different thing”). The El Nino Modoki involves ocean-atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution, analogous to the Southern Oscillation in the case of El Nino. Hence the total entity is named as El Nino–Southern Oscillation (ENSO) Modoki. The ENSO Modoki events significantly influence the temperature and precipitation over many parts of the globe. Depending on the season, the impacts over regions such as the Far East including Japan, New Zealand, western coast of United States, etc., are opposite to those of the conventional ENSO. The difference maps between the two periods of 1979–2004 and 1958–1978 for various oceanic/atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline. This appears to be a cause of more frequent and persistent occurrence of the ENSO Modoki event during recent decades.

2,340 citations

Journal ArticleDOI
TL;DR: The Simple Ocean Data Assimilation (SODA) reanalysis of ocean climate variability is described in this article, where a model forecast produced by an ocean general circulation model with an average resolution of 0.25° 0.4° 40 levels is continuously corrected by contemporaneous observations with corrections estimated every 10 days.
Abstract: This paper describes the Simple Ocean Data Assimilation (SODA) reanalysis of ocean climate variability. In the assimilation, a model forecast produced by an ocean general circulation model with an average resolution of 0.25° 0.4° 40 levels is continuously corrected by contemporaneous observations with corrections estimated every 10 days. The basic reanalysis, SODA 1.4.2, spans the 44-yr period from 1958 to 2001, which complements the span of the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA-40). The observation set for this experiment includes the historical archive of hydrographic profiles supplemented by ship intake measurements, moored hydrographic observations, and remotely sensed SST. A parallel run, SODA 1.4.0, is forced with identical surface boundary conditions, but without data assimilation. The new reanalysis represents a significant improvement over a previously published version of the SODA algorithm. In particular, eddy kinetic energy and sea level variability are much larger than in previous versions and are more similar to estimates from independent observations. One issue addressed in this paper is the relative importance of the model forecast versus the observations for the analysis. The results show that at near-annual frequencies the forecast model has a strong influence, whereas at decadal frequencies the observations become increasingly dominant in the analysis. As a consequence, interannual variability in SODA 1.4.2 closely resembles interannual variability in SODA 1.4.0. However, decadal anomalies of the 0–700-m heat content from SODA 1.4.2 more closely resemble heat content anomalies based on observations.

1,614 citations

Journal ArticleDOI
01 Mar 1980-Nature

1,327 citations