Journal of the Georgian Geophysical Society,
Issue B. Physics of Atmosphere,Ocean and Space Plasma, v.12, 2008, pp.
Simulation and forecast of hydrophysical fields in the part of the
Georgian Black Sea coastal zone
Avtandil A. Kordzadze, Demuri D. Demetrashvili
M. Nodia Institute of Geophysics, 1,Alexidze Str., 0193, Tbilisi, Georgia,
e-mail: akordzadze@yahoo.com, demetr_48@yahoo.com
Abstract
A 3-D baroclinic model of the Black Sea dynamics was adapted and successfully tested for simulation
and forecast of the Black Sea circulation and thermodynamic fields in the part of the Georgian
coastal zone (1 km resolution) within the International project ARENA. A pilot experiment on
functioning of the Black Sea Nowcasting/Forecasting System in the near-real time regime has been
carried out for the first time in the Black Sea region during 22-26 July 2005. This regional model was
nested in a basin-scale model (BSM) of Marine Hydrophysical Institute (MHI) of Sevastopol
(Ukraine). All input data required for 2-days forecasts were obtained from MHI by means of Internet.
Comparison of results of forecasts computed from BSM and high resolution nested grid model showed
that the improvement of the spatial resolution together with other factors is very important in order
to adequately reproduce coastal eddies of small sizes near the Georgian seashore.
1. Introduction
At the present time an ecological situation of the Black Sea is in the disturbing conditions and its
pollution level is considerably growing. Especially shelf and coastal zones of the sea are, in most
cases, areas of the intensive anthropogenic loading [1, 3]. Here there are processes of dispersion and
transformation of polluting substances, lithodynamical processes (transport of the weighed and
carrying deposits, erosion of coast, formation of beaches), physical and chemical processes, etc. The
studying and forecast of such processes is closely connected with understanding and forecasting of
circulating processes. Ability to diagnose and predict the marine environment state allows to make
operatively administrative decisions and to avoid negative consequences of anthropogenic influence.
Development of the Black Sea Nowcasting/Forecasting System was one of the main objects of
the International project ARENA funded by EU. The first stage in the realization of this object was
testing of this System in the near-real time. A pilot experiment on functioning of the Black Sea
Nowcasting/Forecasting System in the near real time regime has been carried out for the first time in
the Black Sea region from 22 till 26 July 2005 within the project ARENA [4]. Leading
oceanographyc scientific teams of all Black Sea riparian countries (Bulgaria, Georgia, Romania,
Russia, Turkey, Ukraine) participated in the pilot experiment. One of the principle parts of the
experiment was calculation of forecasts of hydrophysical fields with high resolution in the Georgian
sector of the Black Sea. With this purpose the 3-D baroclinic prognostic model of the Black Sea
dynamics [5-8] was adapted to the some part of the Georgian Black Sea coastal zone and was nested in
a basin-scale model of the Black Sea dynamics (BSM) of Marine Hydrophysical Institute (MHI,
Sevastopol/Ukraine). This nested grid regional model was applied for simulation and forecast of the
Black Sea regional circulation and thermodynamic fields with 1 km resolution. It should be note that
the basin scale model [5-8] may be consider as continuation of previous works [9-11] on simulation of
dynamical processes in the Black Sea based on the full system of ocean hydrothermodynamic
equations
In this paper the methodology of realization of nested grid modeling and results of forecasts of
hydrophysical fields in the Georgian nearshore zone of the Black Sea are presented.
2. Methodology of functioning of Nowcasting/Forecasting System
The essence of the international scientific and technical experiment was the following [4]. In
the appointed day in the National Hydrometeorological Administration of Romania started atmosphere
forecasting System ALADIN, which gave the information about the atmosphere current condition
over the Black Sea, and also its forecast for two days. This data were transmitted by means of
Internet in MHI, where 2-days marine forecasts were calculated for entire Black Sea basin on the basis
of BSM of MHI. After finishing of calculations, these calculated prognostic data were transferred in
the Marine Research Centres of all the riparian countries including M. Nodia Institute of Geophysics
(Tbilisi, Georgia). In these Centres these data were entered into regional mathematical models with
the purpose to calculate 2-days marine forecasts in the separate local areas with high resolution. The
results of marine forecasts, obtained from regional models, were transferred in MHI, where were
analyzed and located on the Internet site.
3. Simulation and forecast of regional circulation
Simulation and forecast of regional circulation processes in the Georgian near-shore zone of
the Black Sea was carried out on the basis of the regional model (developed on the basis [5-8]), which
was nested in the grid of BSM of MHI. The regional area was limited by Georgian coastline and liquid
boundary along 410E covering Sokhumi, Poti and Batumi ports.
3.1. Model description
The regional nested grid model of the Black Sea circulation is based on the full system of the
ocean hydrothermodynamic equations in hydrostatic approximation. The equations are written in zcoordinates for deviations of thermodynamic values from their standard vertical distributions.
Atmospheric forcing is taken into account by boundary conditions on the sea surface considered as a
rigid surface, where the wind stress components are given as known functions, for temperature and
salinity the Neumann conditions are used by given of heat fluxes, evaporation and atmospheric
precipitations. On the sea bottom the velocity components, heat and salt fluxes are equal to zero
On the lateral surfaces, limiting the area of solution, two following kinds of boundary
conditions are considered: a) On the rigid boundaries, shearing the sea basin from land, components of
current velocity, gradients of temperature and salinity normal to boundary surface are equal to zero; b)
On the liquid boundary, values of velocity, temperature and salinity obtained from BSM of MHI were
used.
The coefficient of horizontal turbulent viscosity is assumed as a function of a horizontal grid
step and horizontal gradients of velocity components [12], and for the definition of turbulent heat and
salt diffusion coefficients the modified Obukhov’s formula is used [13].
3.2 Method of solution
The existence and uniqueness theorems of 3D nonstationary problem of sea dynamics are
established in [14-16]. For numerical solution of the problem two-cycle splitting method regarding
physical processes, coordinate planes and lines is used [17, 18].
3.3 Methodology of nested grid modelling and input data
At realization of the suggested regional model for the local area the sea surface was covered with a
grid using horizontal constant step equal 1 km and grid nodes 69 and 203 along axes x and y,
respectively. On a vertical the non-uniform grid with 27 calculated levels on depths: 1, 3, 5, 7, 11, 15,
25, 35, 55, 85, 135, 205, 305, …, 1505 m were considered. Time step t  1 h.
All input data needed for forecast of hydrophysical fields were obtained from MHI on a grid of
BSM with 5 km spacing. These input data represented the initial fields corresponded to the Georgian
water area and two-hour-step data of forecast obtained by BSM and atmosphere forcing data during 48
hours. Particularly, these data were following: (1) Wind stress components on the Black Sea surface,
(2) surface heat fluxes, (3) evaporation, (4) precipitation, (5) 3-D hydrophysical fields (temperature,
salinity, current velocities) as at initial moment t=0, also their prognostic values (obtained from BSM)
for oar location area.
During realization of the nested grid model the received 3-D initial fields and atmosphere
forcing data were interpolated from the grid of BSM (with 5 km resolution) to the grid of nested grid
model (with 1 km resolution). Besides, after each 2 hours during integration from 3-D prognostic
hydrophysical fields have been obtained lateral boundary conditions for velocity components,
temperature and salinity on the liquid boundary.
The regional model outputs were 1-day and 2-days forecasts of current, temperature and
salinity fields with 1 km spacing on all calculated levels in the Georgian nearshore zone.
4.4 Results of forecast
Before carrying out of the pilot experiment on functioning of near-operational system there was
preparatory stage the main goal of which was joining of the regional model with the BSM of MHI.
With this purpose test numerical experiment on forecast of Black Sea regional circulation was carry
out for time period 7 June, ooh, 2003 – 15 June, 00h, 2003. All needed input data received from
MHI were the same as described in previous section, but there were climatic atmospheric input data
instead of prognostic one. Integration of the model equation system started on 00h, 7 June 2003 with
duration 8 days.
Figures 1-4 show calculated current fields computed from the regional high resolution model
(left side) and from BSM of MHI (right side) at different time moments on depths 5 and 55 m.
8 June 2003, 18 h
(a)
(b)
Fig. 1. Computed current fields obtained (a) from regional model and (b) from BSM of MHI.
on depth of 5m at time moment 18h 8 June 2003.
8 June 2003, 18 h
Fig. 2. The same as in Fig.1, but on depth of 55m.
10 June 2003, 18 h
Fig.3. The same as in Fig.1, but at time moment 18 h, 10 june 2003
10 June 2003, 18 h
Fig.4. The same as in Fig.3, but on depth of 55 m
From comparison of current patterns received from these models it is visible that results of
regional simulation closely follow the simulation of the BSM. The main difference is in the narrow
shelf region - the high-resolution nested-grid model describes well formation of small coastal eddies
while they are not observed in BSM results.
After that, during five days from 22 July till 26 July 2005 the experiment on operational
functioning of the Black Sea Nowcasting/Forecasting System has been carried out. The experiment
started at 12-00 o’clock of 22 July 2005. Every day during this period we calculated forecasts of
hydrophysical fields (currents, temperature, salinity) for 48 hours and placed results of calculations on
ftp-site for the time moments of 24 and 48 hours after the beginning of calculations.
To illustrate the results of forecast there are presented prognostic fields in case of following
forecast times:
12-00 h, 22 July – 12-00 h, 24 July and 12-00 h, 26 July – 12-00 h, 28 July
Forecast time: 12-00 h 22 July - 12-00 h, 24 July
23 July 12-00 o’clock
Fig.5. Calculated fields of current, temperature and salinity on the sea surface at 12-00
o’clock, 23 July 2005.
Fig.6. The same as in Fig.5, but on depth of 25 m
Forecast time: 12-00 h 26 July - 12-00 h, 28 July
28 July 12-00 o’clock
Fig.7. The same as in Fig.5, but at 12-00 o’clock, 28 July 2005.
Fig.8. The same as in Fig.7, but on depth of 10 m.
The analysis of results of marine forecasts, which was carried out in MHI, has shown, that
results of the forecast are in the good agreement with observational data. It is necessary to notice that
the conducted International scientific and technical experiment on functioning of the Black Sea
Nowcasting/Forecasting System has caused wide interest and both its scientific and practical value
has been highly appreciated by experts-oceanologists of the Black Sea riparian countries [19].
5. Summary
The pilot experiment on operational functioning of the Black Sea Nowcasting/Forecasting
System has been carried out for the first time for the Black Sea region, which showed that developed
system can function in the near-real time regime. In this experiment, which is carry out in the
framework of the International project ARENA, forecast of hydrophysical fields in the Georgian
nearshore zone with high resolution (1 km spacing) were calculated on the basis of the regional nested
grid model developed on the basis [5-8]. Comparison of results of forecasts computed from BSM of
MHI and high resolution nested grid model showed that the spatial resolution increase together with
other factors is very important in order to adequately reproduce coastal eddies of small sizes near the
Georgian seashore.
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Моделирование и прогноз гидрофизических полей в части Грузинской
прибрежной зоны Черного моря
Автандил А. Кордзадзе, Демури И. Деметрашвили
Резюме
Трёхмерная бароклинная модель динамики Чёрного моря была адаптирована и успешно
испытана для моделирования и прогноза циркуляции и термодинамических полей в
определённой части Грузинского сектора Чёрного моря (с разрешением 1 км) в рамках
международного проекта ARENA. В течение 22-26 июля 2005 г. в первые для региона Чёрного
моря был осуществлён пилотный эксперимент по функционированию системы диагноза и
прогноза состояния Черного моря в режиме близком к реальному времени. Эта региональная
модель была вставлена в модель динамики для всего бассейна Чёрного моря (с разрешением 5
км) морского гидрофизического Института (МГИ) национальной Академии наук Украины (г.
Севастополь). В течение проведения пилотного эксперимента все входные данные,
необходимые для прогноза с заблаговременностью 2 дней, получались из МГИ с помощью
Интернета. Сравнение результатов прогноза, полученных из модели МГИ и региональной
модели с высоким разрешением, показало, что повышение пространственного разрешения
модели вместе с другими факторами является необходимым шагом для того, чтобы адекватно
воспроизводить прибрежные вихри малых размеров в Грузинской прибрежной зоне Чёрного
моря.
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