Summer Drying Problem

A cooperative effort with the Hungarian Weather Service

Holger Göttel and Vera Schlanger (Hungarian Weather Service)


Motivation

Within the EU funded project MERCURE (Modelling European Regional Climate: Understanding and Reducing Errors) a strong bias towards an extensive drying of the soil was detected during summer months in large areas of the Danube river basin. This feature is common to all participating limited area models. The largest differences occur in the Hungarian Lowlands and in the Wallachia.

Start of the cooperation

The Hungarian Meteorological Service (HWS) and Max Planck Institute for Meteorology (MPI-M) established a cooperation to analyse the summer drying problem. The HMS sent two scientists to MPI-M for a period of two months. Their tasks were to compare REMO results against observation data as well as to learn how to use REMO.

Comparison


Comparison


Simulation

24 year high resolution RCM run with REMO - horizontal resolution 1/2 deg., 20 vertical levels - for Central Europe under present day climate conditions. Initial and boundary values are interpolated from ECMWF reanalysis/analysis data between 1979-2002.

First results

First results of this validation are shown below. The validation of REMO shows that:

  • Precipitation fits well to the observations except for late summer months (Fig. 1)
  • Only for the summer months the model overestimates the 2m temperature (Fig. 2)

The results don't differ from the findings of the MERCURE project.

Hungary Preci 01

Figure 1: Precipitation [mm/month] over 16 stations in Hungary. The solid line is the multi station mean of precipitation for all years from 1979-2002. The dashed lines are the min and max of monthly means in precipitation.

Hungary Temp 01

Figure 2: 2m-air temperature [ºC] for 16 Stations in Hungary. The solid line is the multi station mean of temperature for all years from 1979-2002. The dashed lines are the min and max of monthly means in temperature.

Next Steps


Other meteorological fields (e.g. pressure, 10m wind and surface solar radiation) have been compared to observed data. The model data shows a slight overestimation of the 10m-wind velocity and an definitive overestimation of surface solar radiation. The high solar radiation is correlated with the underestimation of cloud cover.



Possible deficiencies:

  • Problems in advection
  • Deficiencies in the convective mass flux scheme

Hypothesis I


The first hypothesis is that probably drier air is transported into this region. For this the advection processes were compared for one month between simulated and driving data.

Figure 3 shows the differences in the advection processes (for 3 days) through Hungary. Comparing the air mass advection for REMO (left panel) and ERA15 (right panel) reveals that in the REMO simulation Hungary is influenced by continental and in ERA15 by mediterranean air. A detailed investigation is in preparation.

Future plans


The reasons for the disagreement between simulated and observed precipitation and temperature in the Danube river basin is not clear yet. The solution is complex and requires a more detailed investigation.

References:


  • Hagemann, S., B. Machenhauer, O.B. Christensen, M. Deque, D. Jacob, R. Jones and P.L. Vidale 2002: Intercomparison of water and energy budgets simulated by regional climate models apllied over Europe, Max-Planck-Institute for Meteorology, Report 338, Hamburg, Germany
  • Jacob, D. 2001: A note to simulation of the annual and inter-annual variability of the water budget over the Baltic Sea drainage basin, Meteorology and Atmospheric Physics 77, 61-73
  • Majewski, D. and R. Schrodin 1994: Short description of the Europa-Modell (EM) and Deutschland-Modell (DM) of the DWD, Quarterly Bulletin, April
  • Roeckner, E., K. Arpe, L. Bengtsson, M. Christoph, M. Claussen, L. Dümenil, M. Esch, M. Giorgetta, U. Schlese and U. Schulzweida 1996: The atmospheric general circulation model ECHAM-4 Model description and simulation of present-day climate, Max-Planck-Institute for Meteorology, Report 218, Hamburg, Germany

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