Precipitation in climate modeling for the Mediterranean region

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1 Precipitation in climate modeling for the Mediterranean region Simon Krichak Dept. of Geophysics Atmospheric and Planetary Sciences, Tel Aviv University, Israel Concepts for Convective Parameterizations in Large-Scale Models: Spectrum or Bulk? Savona, Italy, March 2012

2 Mediterranean region in GCM and RCM

3 Role of extreme precipitation events and persistent precipitation in the Mediterranean climate Some examples of synoptic processes responsible for extreme precipitation in the MR

4 Torrential rains in Israel 4 December 2001 Krichak, S.O., P. Alpert and M. Dayan (2004) Role of atmospheric processes floods in Israel. J. Hydrometeorol., vol. 5, no. 6. pp associated with hurricane Olga in December 2001 flash Krichak, S.O., P. Alpert and M. Dayan (2006), An evaluation of the role of hurricane Olga (2001) in an extreme rainy event in Israel using dynamic tropopause maps, Meteorol. Atmosph. Phys. DOI /s Krichak, S.O., P. Alpert and M. Dayan (2007) A southeastern Mediterranean PV streamer and its role in December 2001 case with torrential rains in Israel Nat. Hazards Earth Syst. Sci., 7, 1 12, 2007.

5 Torrential rains fell over Israel during the period from 00:00 UTC, December 4 to 00:00 UTC December 5, The rains were observed over a narrow coastal region in the northern part of the country (~32.5ºN; 34.7ºE). Up to 250 mm of rain (about 200 mm during the 01:00 UTC 07:00 UTC time interval of December 4) were registered there. No such precipitation intensities have been earlier registered over the area with the annual precipitation amount of about 650 mm.

6 Hurricane Olga 23/11 04/12/2001

7 ( ) NNRP: Large-scale synoptic view

27 Torrential rains in the Eastern Mediterranean due to Active Red Sea Through formation Krichak, S.O., Alpert, P. (1998) Role of Large Scale Moist Dynamics in November 1-5, 1994 Hazardous Mediterranean Weather. Journal of Geophysical Research, v. 103, pp. 19,453-19,458. Krichak, S.O., Tsidulko, M, Alpert, P. (2000) November 2, 1994 Severe Storms in the Southeastern Mediterranean, Atmospheric Research,53, Krichak S.O., Breitgand J.S., Feldstein S.B. (2012) A Conceptual Model for Identification of the Active Red Sea Trough Synoptic Events over Southeastern Mediterranean, J. Appl. Meteorol and Climatol (in press).

30 Characteristic time scales and length scales of several types of atmospheric process. - microturbulent processes have a characteristic length scale of 1 m, - cumulus convection 1 km, - deep convection 10 km, - mesoscale processes (like tropical cloud clusters) 100 km - synoptical disturbances 1000 km to km. After Tiedke 1984

31 After Tiedke Figure 2. Spectrum of the horizontal wind velocity. After van der Hoven (1957). 1 the spectrum s(f) has a maximum at high frequencies (f ~50 hrs^-1) which corresponds to microturbulent flow of length scales of 1 m to 100 m ( f = 1/ԏ) is the frequency, ԏ is the period of oscillation, s(f) is the spectral energy density). The smallest scales resolved in a forecast model fall into this spectral interval, so that the spectral region around the first energy maximum belongs entirely to the subgrid-scale 2 Another maximum is found for very long periods (ԏ = 4 days) which reflects synoptical disturbances. 3 A third weaker maximum appears at a period of ԏ = 12 hrs which is that of diurnal oscillations. 4 We also observe a broad interval of small values around a period of ԏ=30 min with a corresponding length scale of L = 10 km ( l = u* ԏ)..

32 Convective Processes Convective processes occur at horizontal scales on the order of 1-km. RCMs are typically run at resolutions 1-2 orders of magnitude greater. So, a parameterization is necessary

33 Convective Processes Convective processes occur at horizontal scales on the order of 1-km. RCMs are typically run at resolutions 1-2 orders of magnitude greater. So, a parameterization is necessary But the resolutions are totally different in present NWP, RCM and GCM models!!!!

34 The boundaries of limited area models are artificial. In general there is no rigorous, well-posed way to formulate the boundary conditions (except idealized, e.g. periodic).

35 And even more important - by selecting the size and location of an RCM domain, one determines which part of synoptic processes actually controlling climate in a region is accounted. Krichak, S.O., Alpert, P Kunin, P. (2010) Numerical Simulation of Seasonal Distribution of precipitation over the Eastern Mediterranean with a RCM. Climate Dynamics, 34, 47-59, DOI /s x

37 Optimal domain. Krichak, S.O., Alpert, P Kunin, P. (2010) Numerical Simulation of Seasonal Distribution of precipitation over the Eastern Mediterranean with a RCM. Climate Dynamics, 34, 47-59, DOI /s x

38 Mesoscale atmospheric dynamics, especially the development and propagation of mesoscale convective systems (MCSs), are among the primary driving mechanisms during cool season in the southern Mediterranean region. MCSs result from upscale growth of convective elements O(1 10 km) into mesoscale circulations O(100 km). Idealized numerical experiments suggest that explicit simulation of this process of virtual warming and other precipitation processes in MCSs requires horizontal grid point spacing <1 km. Results from RCM simulations show a failure by RCMs to reproduce observed precipitation patterns associated with MCSs; some RCM results lack propagating nocturnal precipitation signals and others fail to produce a nocturnal maximum of precipitation rate.

40 With high resolution it is possible

41 With high resolution it is possible.

The diurnal cycle of precipitation shows the time integrated influence of various climate factors including, but not limited to, topography, insolation, and mesoscale dynamics.

42 The diurnal cycle of precipitation shows the time integrated influence of various climate factors including, but not limited to, topography, insolation, and mesoscale dynamics. Thus, the ability to reproduce the observed diurnal cycle can serve as a diagnostic measure of the ability of RCMs to accurately simulate sub-daily processes, and has direct importance for climate change impacts assessment Anderson, Arritt, Kain (2007) An Alternative Mass Flux Profile in the Kain Fritsch Convective Parameterization and Its Effects in Seasonal Precipitation

43 Summary A further progress in the RCM appears to be depending on that in the development of specially designed physical parameterization approaches allowing for successful representation of sub-grid processes in medium resolution (comparing to the GCM and NWP) models. In particular, development of convective parameterization approaches allowing for the reproduction of the observed diurnal cycle in precipitation (including accurate representation of the MCSs) and simulation of sub-daily processes over the geographic area which controls the climate conditions in the Mediterranean climate in RCM applications appears to be necessary.

WRF MODEL STUDY OF TROPICAL INERTIA GRAVITY WAVES WITH COMPARISONS TO OBSERVATIONS. Stephanie Evan, Joan Alexander and Jimy Dudhia.

WRF MODEL STUDY OF TROPICAL INERTIA GRAVITY WAVES WITH COMPARISONS TO OBSERVATIONS. Stephanie Evan, Joan Alexander and Jimy Dudhia. Background Small-scale Gravity wave Inertia Gravity wave Mixed RossbyGravity