VERIFICATION OF HIGH-RESOLUTION MESOSCALE SIMULATIONS USING LAND-SURFACE TEMPERATURE FIELDS DERIVED FROM SATELLITES

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1 VERIFICATION OF HIGH-RESOLUTION MESOSCALE SIMULATIONS USING LAND-SURFACE TEMPERATURE FIELDS DERIVED FROM SATELLITES M.A. Jiménez and J.Cuxart Universitat de les Illes Balears Palma de Mallorca, Spain

2 ü Objective: to study the local nocturnal circulations at the basin scale under (nocturnal) stably stratified conditions. ü Clear skies and weak pressure gradient conditions are considered to favour the development of local circulations. ü High-resolution mesoscale simulations using the Meso-NH model (Lafore et al., 1998). Resolutions: Horizontal: 1km x 1km Vertical: 3m close to the surface and stretched above Simulations computationally very expensive. ü Verification: surface observations and LST derived from satellite images (NOAA, MODIS and MSG)

3 Nocturnal meso-beta and katabatic flows in the island of Majorca 125 km Δ = 1 km Δ = 5 km 100 km Case of study from April, 28th 2005 at 1200 UTC to April, 29th 2005 at 1200 UTC (24 hours) Cuxart et al. (MWR, 2007); Jiménez et al. (MWR, 2008)

4 MODEL OUTPUTS at 0000 UTC During the night-time the local effects, such as the topography, are the responsible of the organization of the flow at lower levels. The air flows down from the mountains to the sea, following the terrain, in agreement with the observations. 10m-wind vectors The wind over the Island is weak but, at the slopes, katabatic winds are formed (Martínez and Cuxart, 2009). 1.5m- temperature (K) 10m-wind speed (m s -1 )

5 VERIFICATION USING SURFACE OBSERVATIONS (poorly dense network)

6 VERIFICATION USING NOAA IMAGES (at 0330 UTC) MODEL NOAA The model is able to reproduce the coldest areas in the centre of the basins as it is seen by the NOAA The differences might be related to the representation of the physical processes in the model but also that the frost formation can introduce errors in the satellite-derived LST.

7 10km inland small and closed valley at the seashore

8 % vegetation Satellite MesoNH The vegetation in the model physiographic fields (climatological values) might be different to the amount of vegetation of the simulated day. If vegetation then surface temperature.

9 MODIS MSG LST derived from MODIS and MSG on January, 28 th 2008 at 2200 UTC The LST derived from MODIS has a better spatial resolution than those derived from MSG but there are only 1 or 2 pictures per night MODEL

10 LOCALLY-INDUCED FLOWS AND FOG FORMATION IN THE EBRO RIVER VALLEY ü Fog radiation episodes are very common in this region during winter time and they can last for several days. The fog event from 10th to 12th December 2009 is taken here. ü The model outputs are verified using the dense network of surface observations, satellite-derived LST and a WindRASS profiler located close to Lleida. ü The run is made at 2km x 2km horizontal resolution. Further details are found in Cuxart and Jiménez (2012) and in Cuxart et al. (2012).

11 Dec., 11 th at 2140 UTC SURFACE OBSERVATIONS OF THE FOG EVENT WEAK WINDS NO DIURNAL CYCLE The fog started during December, 10 th 2009 but it covered the whole basin during December, 11 th REDUCED SOLAR RADIATION RH CLOSE TO 100%

12 The fog extension can be estimated from the satellite observations. The white areas of the satellite-derived LST are missing values that are identified as fog or cloud areas, in this case. The MSG LST fields are colder than those derived by MODIS because no water vapour correction is applied in MSG.

13 Conclusions ü It is difficult to verify mesoscale simulations under clear-skies and weak wind conditions due to the local effects play a very important role. The surface observations are typically placed in a non-representative locations and the model at 1km is not able to reproduce these local scales features. ü The satellite-derived LST fields are used to verify the model outputs. The MODIS products are at a horizontal resolution similar to the model outputs although there is only 1or 2 pictures per night. The temporal evolution can be compared using LST MSG, although the spatial resolution is coarser. ü It is found that the model is able to reproduce the LST patterns although on average the modelled temperatures are warmer than those derived by the satellites. Why: 1) Model parameterizations? 2) Fog and frost formation can perturb the satellite-derived LST? Errors in the algorithms? Uncertainity? ü The climatological values of the vegetation in the model surface database might not correspond to the real vegetation for a particular run. These different amounts of vegetation can induce differences in the surface energy budget and, consequently, errors in the characteristics of the surface layer.

14 LST fields extracted from: * MSG (LSA SAF) Land Surface Analysis Satellite Applications Facility * MODIS (terra & aqua, EOSDIS) NASA s Earth Observing System Data and Information System Is there any other place to get other LST products (1km)?

15 As a final user (research): 1)No matter the format if a software is provided (ie hdf5 hdfviewer) 2)A summary of the available LST products with the internet address 3)A short description of period, interval, resolution, algorithm refferences, THANKS!