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3rd HyMeX workshop 1-4 June 2009 Heraklion (Gournes), Crete-Greece

Investigation of dynamic and thermodynamic processes of western Mediterranean cyclones leading to high impact weather (HIW)

Ulrich Corsmeier (Karlsruhe Institute of Technology, KIT); Norbert Kalthoff, Christoph Kottmeier

Motivation and objectives

Synoptic-scale weather systems, in particular cyclonic vortices, most efficiently transport water, energy, and momentum in mid latitudes and thus critically affect the regional and global water cycles and energy redistribution. They also play a crucial role in the transport of trace gases and aerosols. Under certain conditions of the atmosphere (shear, stability, baroclinicity) and of the geographical factors they can develop to high impact weather systems causing damage due to impacts of high wind speed, heavy precipitation, and associated flooding (Homar et al., 2006). It has to be expected that a significant part of the human impact on climate change is experienced through changes in such tropospheric weather systems. A critical region in this respect may be the western Mediterranean Sea, where lower tropospheric cyclones develop regularly, being associated with large amplitude upper-level troughs that extend southwards enforcing transport between the mid latitudes and the subtropics.
The Mediterranean cyclones are often leading to enforced vertical moisture transport and mesoscale lifting accompanied with embedded convection and subsequent heavy precipi-tation. In some cases flash floods south of the Alps occur (Buzzi and Foschini, 2000). These cyclones are difficult to analyse and to predict and there are many factors associated with their development, evolution, and predictability that are incompletely investigated and poorly understood. This results in imprecise forecasts, which might lead to economic as well as ecologic losses in the area affected by such weather and climate.
The scale of the systems to be investigated ranges from mesoscale γ (convection, embedded convection, squall lines) to the synoptic scale (MCCs, Mediterranean depression). That means, the cyclones and convective systems cover a wide range from about one km to several thousand km as well as forecast times from nowcasting to medium-range. Process studies measuring the decisive parameters therefore have to be made on equivalent scales. It is foreseen to concentrate on four typical synoptic scenarios: (i) high amplitude trough approaching the Mediterranean from the west, (ii) remnant circulation in the lower troposphere reactivated by an upper tropospheric trough, (iii) streamer reaching the Mediterranean without cyclogenesis, and (iv) lee-cyclogenesis south of the Alps.

The scientific goal of the project is to investigate the essential dynamical and thermo-dynamical mechanisms of HIW-cyclones by measurements with the new long range and high altitude German research aircraft HALO and by model simulations using the NWP model COSMO-DE. Additionally the research aircraft DO 128 will operate close to the sea surface for measurements of turbulent fluxes before, during and after the passage of cyclones. A meteorological surface station equipped with remote sensing (lidar, radar, radiometer) and in situ instruments (radiosondes) will deliver background data on longer term. Better understanding of the governing flow patterns and their appropriate prediction give reason to reduce the damages and air pollution risks associated with the processes mentioned and therefore might be beneficial in ecological and economical aspects.
HyMeX-Whitebook relevant topics addressed in this proposal (WG 3.3, WG 3.4)

o Documentation of the nature, organization and life cycle of precipitating systems
o HPE space-time structure
o Better understanding the role of upper-level dynamics on HPEs
o Characterization of the low-level mesoscale environment
o Understanding the role of the complex orography of the region
o Identifying mechanisms leading to high-accumulated surface rainfall
o Moisture monitoring
o Identification of water vapour origin
o Role of mid-level dry air masses
o Impact of sea surface temperature and thermal heat content on HPE and cyclogenesis
o Validation of surface fluxes parameterizations
o Multi-scale space-time series of near-surface winds, temperature and humidity
o Quantification of strong-wind induced heat advection
o Variability of intense air-sea exchange
o Air-sea exchange parameterizations

IMK equipment to be deployed during HyMeX – SOP
• Research aircraft HALO (including drop sondes) within the framework of NEPTUN
• Research aircraft DO 128 (including measurements of turbulent fluxes in the PBL and SST)

IMK supersite (suggested location at the North coast of Corsica):
• Radiosounding station (profiles of temperature, humidity and wind speed and direction)
• Doppler wind lidar (lower troposphere)
• Doppler wind lidar (PBL)
• Cloud radar
• Surface energy balance station (radiation balance, heat fluxes, soil heat flux)
• Soil moisture and soil temperature at different depths
• Automatic weather stations (several) and a second radiosounding station

Planned Cooperation:
IMK-TRO (internal, S. Jones, K.-J-Lenz, G. Schädler, B. Vogel): Modelling investigations with COSMO-ART (aerosols and convection), COSMO with bidirectional nesting, Research Group PANDOWAE
DLR-IPA (A. Dörnbrack, G. Craig): Thorpex Atlantic Experiment
Univ. Hohenheim (V. Wulfmeyer, A. Behrendt): DIAL, RRL und X-Band-Radar,
Data Assimilation Studies with WRF 4DVAR