EGU General Assembly 2014 Vienna/Austria

27 April – 2 May 2014

Regional Forecasting System of Marine State and Variability of Dynamical Processes in the Easternmost Part of the Black Sea

Avtandil Kordzadze and Demuri Demetrashvili

M. Nodia Institute of Geophysics of Iv. Javakhishvili Tbilisi State University

Tbilisi, Georgia

A Regional forecasting system of the Black Sea state for the easternmost part is developed at M. Nodia Institute of Geophysics of Iv. Javakhishvili Tbilisi State University within the framework of EU International projects ARENA and ECOOP [1-5]. The regional forecasting system is one of the parts of the Black Sea Nowcasting/Forecasting System and enables to calculate 3 days’ forecasts of current, temperature and salinity fields for the easternmost part (including Georgian Black Sea coastal zone) with 1 km spacing. In Fig.1 the scheme of functioning of the regional forecasting system is shown.

The regional forecasting system is based on a high-resolution 3-D regional prognostic model of the Black Sea dynamics developed at the Institute of Geophysics (RM-IG). The model with 1 km grid step, which is based on a primitive equation system of ocean hydrothermodynamics, is nested in the basin-scale model (BSM) of the Black Sea dynamics of Marine Hydrophysical Institute (MHI, Sevastopol/Ukraine) with 5 km grid step [6].

Data needed on open and upper boundaries, also the 3-D initial hydrophysical fields for the easternmost regional area are provided operatively from MHI via ftp site. These data on the open boundary are values of velocity components, temperature and salinity predicted by the BSM of MHI; on the sea surface 2-D meteorological boundary fields predicted by the atmospheric model ALADIN are used.

To solve the problem we used the two-cycle method of splitting the model equation system with respect to both physical processes and coordinate planes and lines, which was proposed to solve problems of ocean and atmosphere dynamics by Marchuk [7, 8].

The regional area of forecasting is separated from the open part by the western liquid boundary coinciding approximately with the meridian 39.08E (Fig.2). There is used a grid having 215 x 347 points on horizons with 1 km spacing. On the vertical the non-uniform grid with 30 calculated levels on depths: 2, 4, 6, 8, 12, 16, 26, 36, 56, 86, 136, 206, 306 ,…, 2006 m are considered. The time step is equal to 0.5 h.

215x347

Fig.1. The scheme of functioning of the regional forecasting system.

Fig.2. The regional area of forecasting.

With the purpose of validating the regional forecasting system comparison of predicted fields with real data have been done during the pilot experiment within the project ARENA in 2005, which showed an ability of the regional forecasting system to predict hydrophysical fields with sufficient accuracy [9]. Currently we are able to carry out a comparison of the calculated SST (sea surface temperature) with SST satellite images derived from NOAA (the marine portal site NSA of Ukraine, http://dvs.net.ua/mp). Some examples of validation of forecasted SST are shown in Fig.3, where periods August and October 2010 are chosen. An analysis of the comparison show good qualitative and quantitative agreement between the forecasted and measured temperature fields; in most points the error does not exceed 0.6-0.8 c.

Fig.3. Forecasted (on the left side) and satellite SST derived from NOAA (on the right side).

Fig.4. Sea configuration and bottom topography of the eastern area used in the model

72 h forecasts of sea current predicted by RM-IG (Tbilisi/Georgia)

Predicted by BSM of MGI (Sevastopol/Ukraine)

Fig.5. Predicted sea surface circulation fields by both RM-IG and BSM of MGI.

The comparative analysis of predicted fields by both RM-IG and BSM of MHI shows that to use the model with high resolution is very important factor for identification of coastal eddies of small sizes (Fig.5).

Sumulation for 27 November 2013, 00:00 GMT

Sea flow SalinityTemperature

Fig. 6. Predicted sea surface circulation (a), temperature (b) and salinity (c) for 27.11.2013

(a) (b) (c)

Variability of circulation processes in the easternmost part of the Black Sea for 2010-2014

2010

2011

Fig. 7. Predicted sea surface circulation fields for 2010-2011.

2012

2013

Fig. 8. Predicted sea surface circulation fields for 2012-2013.

2014

Fig. 9. Predicted sea surface circulation fields for 2014.

The analysis of simulated and forecasted hydrophysical fields for 2010-2014 period shows that the easternmost water area of the Black Sea represents a dynamically active zone, where the continuous generation, deformation and disapearance of the cyclonic and anticyclonic vortexformations of different sizes occur. In Figs. 7-9 the computed surface current fields from June 2010 to April 2014 are shown.

The analysis of results of simulation and forecast of dynamical processes carried out on the basis of the regional forecasting system for the easternmost part of the Black Sea (including Georgian water area) shows that this water area of the basin is dynamically very active zone, where during all seasons generation, deformation and disappearance of anticyclonic and cyclonic vortex formations of different sizes continuously takes place. The regional circulating processes in the warm and cold periods arein the certain degree different. In the warm period the most intensive vortical formation is frequently well known Batumi anticyclonic eddy which is very stable formation and predetermines a specific hydrological mode in this part of the Black Sea. Most intensive and steady the Batumi eddy was in summer 1010 when was abnormal hot for last decades. The anticyclonic formations similar to the Batumi eddy can also occur in winter season but they are less steady and can not exist for the long period. In most cases, a narrow zone along the Caucasian coast with a width of about 20-30 km is formed, where generation of small unstable eddies with diameter 5-20 km is observed. The comparative analysis of predicted fields by both RM-IG and BSM of MHI shows that to use the model with high resolution is very important factor for identification of coastal eddies of small sizes. vortical formations weaken at strong atmospheric winds which has a smoothing action on sea circulation.

CONCLUSIONS

References

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