wind field in a closed breeze cell in ahtopol - … · the sea breeze is a coastal phenomenon...

Science & Technologies

Volume V, Number 3, 2015 Natural & Mathematical science 25

WIND FIELD IN A CLOSED BREEZE CELL IN AHTOPOL - MODELLING AND

OBSERVATIONS

Hristina Kirova, Damyan Barantiev, Valeri Nikolov, Ekaterina Batchvarova

National Institute of Meteorology and Hydrology,

Bulgarian Academy of Sciences,

66, Tsarigradsko Shose blvd Sofia 1784

ABSTRACT The sea breeze is a coastal phenomenon driven by the temperature difference over land

and sea. This thermally driven circulation is observed mainly during the warm seasons and is

characterized with specific wind and temperature conditions influencing all social and economic

activities. Two simulations with the Weather Research and Forecasting (WRF) model with different parameterizations of physical processes are performed and the results are compared

with data from a sodar at Ahtopol. Three days with closed breeze cell are chosen for the study.

The model simulates the wind field adequately in some of them and poorly in others. Key words: closed breeze circulation, vertical profiles, SODAR, WRF

INTRODUCTION

Life in coastal areas is influenced by the sea breeze in different ways: it affects dispersion of

pollutants, distribution of airborne insects, spread of pollens etc. The sea breeze is a thermally

driven circulation, observed mainly during the warm part of the year. The development of the sea

breeze depends on a variety of physical, climatic, orographic conditions (Simpson, 1994). The

breeze influences different recreational (e.g. gliding, ballooning, sailing) and economic activities

determining the importance of studying the phenomenon using long series of measurements and

numerical mesoscale models. Here we investigate the ability of Weather Research and Forecasting

(WRF) model to simulate wind field in a closed sea breeze cell. Tree days with closed breeze cell

are selected: 05.08.2008, 05.09.2008 and 07.05.2009 to be studied. The output of the model is

compared with data obtained by acoustic system for sounding of atmosphere - SCIENTEC Flat

Array middle range instrument (MFAS) sodar with frequency range 1650 – 2750 Hz; 9

emission/reception angles (0°, ±22°, ± 29°); maximum 100 vertical layers; range between 500 –

1000 m; accuracy of horizontal wind speed 0.1 – 0.3 ms-1; range of horizontal wind speed ± 50 ms-

1; accuracy of vertical wind speed 0.03 – 0.1m/s; range of vertical wind speed ± 10 ms-1; accuracy

of wind direction 2 -3 degrees. The climate of the sea breeze circulation based on sodar

measurements have been studied intensively since 2008. The duration of sea breeze at the Southern

Bulgarian coast is about 4 hours, the vertical scale - 600 m, wind speed in the cell is rarely higher

than 5 m/s, observed closed breeze cell are about 6 % per year (Barantiev et al 2013, Barantiev et al.

2011, Batchvarova et al. 2012, Batchvarova et al 2011, , Novitskii et al. 2012 ). The sodar is

operational since July of 2008 at southernmost site at the Bulgarian Black sea coast under a

Bulgarian – Russian joint project between the National Institute of Meteorology and Hydrology -

Bulgarian Academy of Sciences (NIMH-BAS) and the Research and Production Association (RPA)

Figure 1. The meteorological observatory Ahtopol.



“Typhoon” in Obninsk, which is part of the Russian Federal Service on Hydrometeorology

and Environmental Monitoring (Roshydromet).

The sodar is located at meteorological observatory (MO) of Ahtopol (NIMH - BAS) about

400 m inland, 30 m above the sea level. It is mounted on the roof of station building (Figure 1). In

the vicinity of the station the coastline is oriented from NNW to SSE which determines that the

marine conditions are represented by the flows from the sector 0 – 150 degrees (air mass intrusions

from the sector 0-150 degrees represent intrusions from the sea).

MODEL SET UP

Simulations are performed with the Weather Research and Forecasting (WRF) model with

dynamical Advanced Research WRF (ARW) core, version 3.3.1 (Skamarock et al., 2008). The

initial and boundary conditions are provided by the US National Center for Environmental

Prediction Final Analyses (FNL) model with 1x1 degree spatial and 6 hours temporal resolution.

Details on model configuration are described in Table 1. For both configurations (WRF1 and

WRF2) two- way interactive nesting is applied which allows exchange of information between

nested domain and its parent one (Figure 2). The model top is set to 50 hPa. The number of vertical

levels in WRF1 is 50, in WRF2 – 43.

Figure 2. Configuration modelling domains (WRF2) and terrain features of the innermost one.

Table1. Physical options for WRF1 and WRF2 simulations WRF1 WRF2

Microphysics

95 (D1&D2), 5(D3&D4)= Eta

microphysics

8 (D3&D2)= Thompson

graupel scheme; 4(D1)=WSM

5-class scheme Longwave radiation 1 = RRTMG 1 = RRTM

Shortwave radiation 2 = RRTMG 2 = Goddard

Surface layer 2 = Eta similarity 2 = Eta similarity Land surface 1=thermal diffusion scheme Noah LSM

PBL 2 = Mellor-Yamada-Janjic (MYJ)

2 = Mellor-Yamada-Janjic

(MYJ)

Cumulus parameterisation 5 = New Grell (only for D1, D2, D3) 5 = New Grell (D1 & D2)

Urban physics 3 – category Urban Canopy Model



MODEL RESULTS

Evolution of breeze cells is examined through vertical cross –sections of zonal-component of

wind speed (U), wind speed (Wsp), Wdir - wind direction and vertical component of the wind speed

(W) (Figure 3). Both configurations of WRF simulate the observed structure with some delay in

time and with different spatial scale in vertical. WRF1 patterns are with smaller size but closer to

the measured ones, except for W. Sodar WRF1 WRF2

a)

b)

c)

Figure 3. Vertical crossection (07.05.2009) of zonal component of the wind speed a); wind speed b); wind

direction c); vertical component of the wind speed d).

The ability of presented configurations to reproduce the vertical structure during well

recorded closed breeze cells is studied by comparing the model output at every level with

measurements. For every level the correlation coefficient (r) is calculated (Figure 4). The best



overall performance is obtained for the event of 07 May 2009.The lowest values for correlation

coefficient are obtained for the vertical wind speed. As a whole the most stable parameter for

WRF2 simulation is the zonal component of the wind speed.

WRF1 WRF2

05 A

ugu

st 2

008

05 S

epte

mb

er 2

008

07 M

ay 2

009

Figure 4. Variability of the correlation coefficient with height



CONCLUSIONS:

Development of the sea breeze on the Southern coast of Bulgaria has been simulated with

WRF (ARW) and model outputs have been evaluated against data from sodar. Two configuration of

WRF have been applied with widely used Mellor-Yamada-Janjic planetary boundary layer schemes.

Both model configurations reproduced the observed structure shifted in time and with

different vertical scale. WRF1 qualitatively overperforms WRF2 but in the same time better

correlation is achieved for studied parameters for WRF2.

Acknowledgements. This work is result of intergovernmental agreement for scientific

cooperation between Bulgaria and Russia,and in particular it is a part of a research project initiated

between the National Institute of Meteorology and Hydrology – Bulgarian Academy of Sciences

(NIMH-BAS) and the Research and Production Association (RPA) “Typhoon” – Russian Federal

Service on Hydrometeorology and Environmental Monitoring (Roshydromet). This paper has been

prepared with the financial support of the European Social Fund through Project *ВG051РО001-

3.3.06-0063*.NIMH - BAS is solely responsible for the content of this document, and under no

circumstances can be considered as an official position of the EU or the Ministry of Education and

Science.

LITERATURE

1. Barantiev, D., E. Batchvarova, M. Novitsky, (2013). Exploration of the Coastal Boundary

Layer in Ahtopol through Remote Acoustic Sounding of the Atmosphere, paper in conference

proceedings, 2nd National Congress on Physical Sciences, Section: Physics of Earth, Atmosphere

and Space (S07.26), 25-29 September 2013, Sofia, Bulgaria

2. Barantiev D, M Novitsky, E Batchvarova, (2011). Meteorological observations of the

coastal boundary layer structure at the Bulgarian Black Sea coast, Adv. Sci. Res., 6, 251-259

3. Batchvarova, E., D. Barantiev, M. Novitsky, (2012). Costal Boundary layer wind profile

based on SODAR data – Bulgarian contribution to COST Acton ES0702, paper in conference

proceedings, The 16th

International Symposium for the Advancement of Boundary-Layer Remote

Sensing – ISARS 2012, 5-8 June 2012, Boulder, Colorado, USA

4. Batchvarova, E., D. Barantiev, M. Novitzky, 2011: Characteristics of the sea breeze at the

southern Bulgarian Black sea coast based on sodar and eddy correlation measurements.

Energy&Meteorology - Weather and Climate for the Energy Industry, ICEM2011, 8-11 November,

Surfers paradise, Queensland, Australia, p.64

5. Novitskii M. A., Kulizhnikova L. K., Kalinicheva O. Yu., Gaitandzhiev D., Barantiev, D,

Bachvarova E, Krysteva, K., (2012). Characteristics of wind speed and wind direction in the

atmospheric boundary layer on the southern coast of Bulgaria, Russian Meteorology and

Hydrology, 37, 159-164.

6. Simpson J. E: Sea breeze and local wind, 1994. Cambridge University Press

7. Skamarock W., J. B. Klemp, J. Dudhia, D. O. Gill, D. M. Barker, M. G. Duda, Xiang-Yu

Huang, W. Wang, J. G. Powers, 2008. A Description of Advanced Research WRF Version3

http://www.mmm.ucar.edu/wrf/users/docs

wind field in a closed breeze cell in ahtopol - … · the sea breeze is a coastal phenomenon...

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