The extreme phenomena and the thresholds for the values of corresponding parameters, by definition, vary from place to place for natural reasons (different climates), because the extreme value of given meteorological parameter at one place, can be within the normal range at another place. A reason to apply different values is their application to socio-economic activities and needs, which also differ with climate. Although the extreme meteorological events do not occur often, they could be dangerous and harmful for the health of people, can cause large infrastructure damages, can influence the economics and cause loss of human life. Therefore, to study, understand, and to characterize the extreme meteorological events and the climate of extremes in time and space with using specific methodologies for their definition and to identify corresponding thresholds is of primary interest for meteorologists worldwide.
For prevention from the hazardous meteorological events which happen more often during last years (heavy rains, extreme temperatures, high winds) and cause significant socio-economic costs, many governments invest in the development of effective systems for observations and forecasting of such events, taking into account the variability of climate, climate change and the need to adapt to them. The results of research in this field are of great importance for adequate action of governments and businesses to reach better management and reduction of risks.
Coastal zones – challenging task for numerical models
The ABL structure in coastal regions is studied in many countries as many cities and industrial zones are located at the coasts of oceans, seas, or large lakes. The variety of physical, geographical, and climate conditions, as well as meteorology, is large, so there is a constant need for improvement of the weather forecasts. Within the ABL the exchange of energy between the surface and the atmosphere is taking place and all processes are influenced by the characteristics of the surface. The abrupt change in surface (such as field-city, sea-land, field-forest, etc.) leads to complexity in atmospheric processes in coastal areas, which is characterized by the transformation of the air masses (AM) to the physical characteristics of the new surface. The theoretical description of such type atmospheric processes under complex terrain and local circulations is difficult due to the complex layering of the ABL in coastal areas and therefore the numerical modelling of the meteorological processes is difficult as well. Most ABL parametrizations are derived and tested for flat homogeneous terrain and they are incorporated in mesoscale models as such. Hence, in coastal areas, additional validation with high temporal and special resolution observations is needed. The advancement of remote sensing technologies of the atmosphere during the last decade allows improving the quality of data for model validation.
Тhe potential of modern technology
The technological development of different types of ground-based remote sensing instruments for observation of meteorological parameters within the atmospheric boundary layer (ABL) and above it, and it is a basis and a method to obtain more accurate special qualitative and quantitative assessments of the state of the lower layers of the atmosphere at a given moment and to understand the physical processes in it. These instruments provide a wide range of data for initialization, assimilation, and evaluation of the performance of new generation of weather forecast and climate models of high resolution. The ground-based remote sensing instruments data are also important for climatological analysis and a number of applications that need a high spatial and temporal resolution of data.
Data collection and analysis in the coastal ABL using acoustic sounding starts in Bulgaria in summer 2008 at the Experimental polygon (EP) Ahtopol. These high special and temporal resolution measurements allow performing climatological studies of the coastal ABL in Bulgaria. The sodar (SCINTEC Flat Array Sodar MFAS) gives information about a number of wind and turbulence parameters and allows studies of the vertical structure of the coastal ABL up to about 1000 m.