WAVES & TURBULENCE IN THE ATMOSPHERE, 2005/06            (Hrvatski)

This is a basic research on interactions between atmospheric buoyancy waves and turbulence, and their relations with other physical processes (radiation, air pollution, surface effects). The project belongs to mountain & coastal meteorology and climatology; arguably, this is mesoscale meteorology & micrometeorology. The methods are: numerical & analytical modeling and measurements & data analysis. Turbulence, still one of the principally unsolved problems today, is in the core of our reseach. It appears almost continuously in the Atmospheric Boundary Layer (ABL, the lowest part of the atmosphere, ~1km deep, where we live), through the air-sea interface, and sporadically in the midd- and upper layers characterized with various wave spectra. We want to study the buoyancy waves with horizontal and vertical wavelength ~ 5-200km and 1-5km, respectively, and with the periods from ~ 10min up to 1day. These waves, while interacting with turbulence, modulated by radiation (heating/cooling) and due to surface-characteristics changes (temperature, roughness, slope), determine atmospheric phenomena and ultimately the weather - all for the given large-scale conditions.

We start with observations of fine spatio-temporal resolutions. Based on these, we calculate turbulence fluxes of momentum, heat, moisture, particles and chemical spiecies. The fluxes are essential for analytical & numerical modeling of airflow over complex terrain; moreover, they have immediate applications in various aspects of life (construction work, agro-culture, etc.). Other measurements will be also used in e.g. various model initializations and validations. The models employed will vary in their complexity ranging from the improved analytic models of Prandtl and Ekman (eddy diffusivity treated with the WKB method allows more realistic gradients of the calculated fields), to numerical, nonlinear models such as MIUU (Sweden), MEMO (Greece & Germany), ALADIN (France & associated countries) and COAMPS (USA) with more faithful turbulence parameterizations. Some of these models we already use and some we even improve. With modeling we will show where to measure next time, what to improve in the parameterizations used, and how to develop new theories of airflows over complex terrain.

All that should yield a swift support to the tourism, traffic, hydrology, agro-culture, i.e., to the strategic avenues of the regional development. The emphasis here is on relatively young & energetic scientists already having international experience.

GOAL

-The main goal is to better understand and explain quantitatively some of the basic meso- and microscale processes occuring at coasts and mountains (e.g. three-dimensionality, unsteadiness and turbulence of the bora, scirocco, valley & mountain circulations). Only in this way, it will be possible to forecast the local weather phenomena more reliably, and to understand and project future local climate variations.

-Our overall goal relates to parameterizations improvements in numerical weather-forecasting models. (Processes that cannot be resolved explicitly in the models should be parameterized.  Since the models typically use horizontal & vertical resolution of (dx,dz)~(10km,500m), they intrinsically cannot "see" short waves, turbulence, clouds, fog, i.e. micro-physical processes of condensation, evaporation, etc.). Our goals make a direct basic scientific support to applied research at the Weather Service, see http://www.dhmz.htnet.hr/index.php.

We want to form a solid theoretical background for the regional mesoscale meteorology & microclimatology. The regional meteorological measurements, observations and detailed numerical simulations are still not unified under modern dynamic (theoretic) meteorology today.

PURPOSE

With a better perception of wave-turbulence interactions in the atmosphere over the complex terrain, we will strenghten mesoscale theory; therefore, we will efficiently improve forecasts of the prognostic weather models today. Moreover, developing the theory and providing the model improvements, we would choose the observational sites for future experiments more objectively, as well as the observational areas, periods and durations for intensive field experiments.

The project should give a sound basis for aggressive, long-term development of the local meteorology & climatology. The latter is too important to be ignored.

APPLICATION OF THE RESEARCH

Although firstly of a theoretical & numerical modeling nature, the project has a number of applications. That can be divided into: short-, medium- and long-term applications. Examples for each follow.

(1) Improvement of the weather forecast over the area. With the better understanding of the local meteorological processes, we will improve their parameterizations in the prognostic weather models. Consequently, the models will better predict the local wind, temperature and humidity.

(2) Aiding better meteorological, climatological and ecological studies for road constructions, buildings, etc. Detailed recommendations for possible use of wind energy will be given. The basis for that is an in (1).

(3) Basis for strategic future projections of the regional agro-culture, hydro-culture, etc. for the next few decades. There are some indications that the broader Adriatic area will become drier in average; details are unknown today. The project shall be a part of the basis for future regional studies of climate variations.

The largerst part of these applications will take place under a close collaboration/leadership of the Weather Service of Croatia.  Stengthening the collaboration between our Faculty and the Weather Service is of crucial importance for the applications of the research proposed.

BACKGROUND

Wave-turbulence interactions in the atmosphere and their relations to other processes (radiation, condensation, evaporation, etc.) over complex terrain are not covered well by theory today (Egger 1990; Holton et al. 2003). The real advancement in this field is slow since one deals with coupled nonlinear, unsteady 3D processes. Simultaneously, meso- & microscale phenomenological realizations grow rapidly due to ever better measurements and numerical simulations (e.g. Benard et al. 2000). Nonetheless, the results are difficult to interpret since there is no unifying mesoscale theory today (e.g. Holton 1992).

The east Adriatic coast represents a stepwise change in the surface characteristics where the sea, air and complex terrain meet. Even sea-surface temperature change yields variations in the bora wind (Enger & Grisogono 1998). It is wrong to just simply take up understandings from other coastal ABLs, e.g. from the USA west coast (Tjernström & Grisogono 2000), because everywhere is another island distribution, the coastal terrain and coastline. Thus, we have to conduct local observations and detailed numerical simulations (e.g. Telišman-Prtenjak & Grisogono 2002; Belušić & Bencetić Klaić 2004, Grubišić 2004) while further developing the theory of coastal meteorology. Similar reasoning, with some simplifications, applies to the inland ABL and most of the troposphere. (Bencetić Klaić et al. 2002). There are some indications that significant parts of the understading of turbulence around low-level jets, associated with down- and upslope flows, can be applied over the Dinaric Alps more straightforwardly (Grisogono & Oerlemans 2001a;b). However, very stable ABL and stratified turbulence interacting with short buoyancy waves still remain principally unsolved problems and we want to continue our research in this area too.  It has only recently been revealed that Coriolis effect is significant for nonlinear orographic flows (e.g. Grisogono & Enger 2004). Meanwhile, one finds a wealth of local and flow peculiarities (e.g. Belušić et al. 2006; Telišman Pretenjak et al. 2006).

Integrated effects of the mentioned coastal and orographic circulations onto climate change are poorly understood today. These are probably of cumulative nature on micrometeorology if the effects themselves are mostly local. But if sources deposit their effects far away, i.e. nonlocal effects, maybe hypothesis of a microclimate type will have to be rejected. We will address this problem by estimating various relevant parameters, such as the Rossby radius of deformation, for the relevant mesoscale circulations. To understand the relevant atmospheric processes, dynamic similarities and possible teleconnections, etc., around the Adriatic and Dinaric area, we also learn about similar processes at both high (e.g. Mauritsen et al. 2005, Žagar et al. 2005a) and low (Žagar et al. 2005b) latitudes.

Belušić D., Z.B. Klaić, 2004: Estimation of bora wind gusts using a limited area model. Tellus, 56A, 296-307.

Belušić, D., M. Pasarić, Z. Pasarić, M. Orlić and B. Grisogono, 2006: On local and non-local properties of turbulence in the bora flow. Meteorol. Z.15, 301-306.

Bénard, P., A. Marki, P. N. Neytchev, M. Telišman-Prtenjak, 2000: Stabilization of nonlinear vertical diffusion schemes in the context of NWP models. Mon. Wea. Rev. 128, 1937-1948.

Bencetić Klaić, Z., T. Nitis, I. Kos, N. Moussiopoulos, 2002: Modification of the local winds due to hypothetical urbanization od the Zagreb surroundings. Meteorol. Atmos. Phys., 79, 1-12.

Egger, J. 1990: Thermally forced flows: theory. Atmospheric Processes over Complex Terrain. (Editor: W. Blumen, American Meteorol. Soc., Washington, DC, 43-57)

Enger L., B. Grisogono, 1998: The response of bora-type flow to sea surface temperature. Quart. J. Royal Meteorol. Soc. 124, 1227-1244.

Grisogono, B., J. Oerlemans, 2001a: Katabatic flow: analitic solution for gradually varying eddy diffusivities. J. Atmos. Sci., 58, 3349-3354.

Grisogono, B., J. Oerlemans, 2001b: A theory for the estimation of surface fluxes in simple katabatic flows. Quart. J. Royal Meteorol. Soc. 127, 2725-2739.

Grisogono, B., L. Enger, 2004: Boundary-layer variations due to orographic-wave breaking in the presence of rotation. Quart. J. Royal Meteorol. Soc. 130, 2991-3014.

Grubišić, V. 2004: Bora-driven potential vorticity banners over the Adriatic. Quart. J. Royal Meteorol. Soc. 130, 2571-2603.

Holton, J.R., 1992: An Introduction to Dynamic Meteorology. Academic press, San Diego, 511 pp.

Holton, J.R., J.A. Curry, J.A. Pyle, 2003: Encyclopedia of Atmospheric Sciences. Academic press, Amsterdam, 2780 pp.

Mauritsen, T, G. Svensson, B. Grisogono, 2005: Wave Flow Simulations Over Arctic Leads. Boundary-Layer Meteorology. 117, 259-273.

Telišman Prtenjak, M., B. Grisogono, 2002: Idealised numerical simulations of diurnal sea breeze characteristics over a step change in rougness. Meteorol. Z. 11, 345-360.

Telišman Pretenjak, M., B. Grisogono and T. Nitis, 2006: Shallow mesoscale flows at the north-eastern Adriatic coast. Quart. J. Roy. Meteorol. Soc., In press.

Tjernström, M., B. Grisogono, 2000: Simulations of super-critical flow around points and capes in a coastal atmosphere. J. Atmos. Sci., 58, 108-135.

Žagar, M, G. Svensson, M.Tjernstrom,2005a: High spatial and temporal variability of dry deposition in a coastal region. Envir. Fluid Mech. 5, 357-372.

Žagar, N, E. Andersson, M. Fisher, 2005b: Balanced tropical data assimilation based on a study of equatorial waves in ECMWF short-range forecast errors.Quart.J.Royal Meteorol. Soc. 131; 987– ; 1011.

MEANING OF THE PROPOSED RESEARCH

It is a surprising fact that today we know more about the dynamics of an atom than about the motion of a cubic meter of air or water. Weather & climate research must not be ignored today simply because the whole issue is way too important for nature and human survival. Our questions are simple & basic: why the weather & climate are as they are (only afterwards one may derive a consistent question of prognosis).  In the core of this issue is wave-turbulence interaction (whose consequence is much intensified fluid mixing & transport).

We want to study mesoscale processes (between those directly sensed by humans and that readily seen in synoptic charts). Behind the scenary is a multi-scale essence of geophysical processes: energy cascade among planetary, synoptic (regional), meso- and microscale.  Therefore, this belongs to basic research.

Our research & findings, although basic in its nature, is directly applicable in tourism, traffic, infra-structure, agro-culture, forestry, environmental protection, energetics, etc.  That goes via natural inter-disciplinarity of geophysical processes.

METHODS

We use all three main metods of geophysics in studying atmospheric wave-turbulence interactions: 1) measurements & observations, 2) analytical modeling, 3) numerical modeling (simulations).  While integrating all the three approaches, we strengthen theory and recommend direct applications.

Dept. of Geophysics at Faculty of Science does not have enough AWS but such will be accessible via the Weather Service; that will yield new data sets. Our analytical models are based on linear wave theory (e.g. Nappo 2002), or selected chapters on convection (e.g. Holton 1992), or the WKB theory for the ABLs (Grisogono 1995, Grisogono & Oerlemans 2001). These shall be used in explaining measurements, interpretations of 3D numerical simulations and will be further developed via new M.S. & PhD theses in future. Numerical nonlinear simulations using MIUU, MEMO, MM5, COAMPS and/or ALADIN make the core of our research tools. With fine spatio-temporal model resolutions (~10sec, few km in horizontal, up to a fraction of km in vertical) we shall address various mesoscale phenomena (sea-breeze & other coastal circulations, slope flows, orographic waves, urban circulations, etc.). Besides the observed phenomena, we want to simulate idealized situations too. In this way, via sensitivity tests we shall broaden our initial understanding and formulate possible applications.

Grisogono, B., 1995: A generalized Ekman layer profile within gradually varying eddy diffusivities. Quart. J. Royal Meteorol. Soc. 121, 445-453.

Grisogono, B., J. Oerlemans, 2001: A theory for the estimation of surface fluxes in simple katabatic flows. Quart. J. Royal Meteorol. Soc. 127, pg. 2725-2739.

Holton, J.R., 1992: An Introduction to Dynamic Meteorology. Academic press, San Diego, 511 pp.

Nappo, C.J., 2002: An Introduction to Atmospheric Gravity Waves. Academic press, San Diego, 276 pp.

EXPECTED RESULTS

While the main goal is to better understand meso- and microscale processes at the Adriatic coast & mountains (3D, unsteadiness & turbulence of sea-breeze, bora, scirocco, mountain & valley flows), the results will yield a more reliable forecasting of the local weather (timing, location, intensity, etc.), and to project the related microclimatic variations into future.

The results will have a positive impact on new parameterizations in numerical prognostic models for weather, climate and air quality. With a deeper understanding of wave-turbulence atmospheric interations over complex terrain, the mesoscale theory strengthens; this is probably the most effective way to improve the forecast from the existing weather & climate models as the latter depends strongly on the parameterizations (explicitly unresolved processes in the models such as island circulations, short-slope winds, etc.). In other words, developing theory and consequently improving numerical models gives a sound basis for future climate projections and thus an overall development of the society. For example, one of the results will be a new parameterization of local circulations over the Adriatic area and inland; this will be recommended to the models used routinely for weather forecasting. Another result will be an estimation of the wind energy potential in the surface layer over eastern Adriatic area; this could yield commerical applications later on.

NOTES ABOUT PI: BRANKO GRISOGONO