Atmosphere - Ocean interaction


The atmosphere-ocean interaction plays an important role in climate research. Several aspects of the momentum, heat, mass exchange in both the atmosphere and ocean boundary layers need improvements, Figure 1. This research is done together with scientist at the Department of Earth Sciences, Meteorology at Uppsala University. We use the Baltic Sea modelling and observed fields of temperature, ice and salinity to test and evaluate different aspects of the atmosphere-ocean interaction. Meteorological data including different data sets as well as direct measurements of fluxes from the Östergarnholms site are also used. Below some of our research activities are outlined.

 

(Click image to enlarge)

Click image to enlarge

 

Figure 1. A sketch of the problem considered from an ocean point of view.

 

1. Evaluation of meteorological forcing fields

In some recent studies the SMHI 1° x 1° and the ERA40 gridded meteorological data sets for the Baltic Sea region, were compared and analysed (Omstedt et al., 2005). The two data sets are quit similar and can both be used in Baltic Sea modelling. However, the horizontal resolution is too coarse for resolving marine conditions over the Baltic Sea. This implies, for example, that the ERA40 original surface winds are too low for some Baltic Sea regions. The ERA40 precipitation values are also too low compared with those of the SMHI and other available data.

 

2. Net precipitation and heat flux components

Precipitation and evaporation rates over the Baltic Sea have been analysed during a 12 month period with several methods (Smedman et al., 2005a, Hennemuth et al., 2003) illustrating an estimated net precipitation of 100 ±50 mm for the particular 12 month period. Long-term estimates on net precipitation has been estimated by Rutgersson et al., (2002) indicating a net precipitation of 1500 ±1000 m³/s during the 20th century.

 

3. Test of new parameterization schemes

Recent findings at the department of Earth Sciences, Meteorology, Uppsala, give new ways to parameterise the turbulent heat fluxes (sensible and latent) (Sahlée et al., 2005; Smedman et al., 2005b). They have found a certain regime very close to the neutral stratificated atmosphere - UVCN (Unstable, Very Close to Neutral) regime. In those conditions heat fluxes are enhanced, compared to the traditional theories. To test the new parameterisations of sensible and latent heat fluxes the PROBE-Baltic model was run for different periods (Rutgersson et al., 2005).

 

References:

  • Hennemuth B., Rutgersson, A., Bumke K., Clemens, M., Omstedt A., Jacob D., and A-S Smedman (2003) Net precipitation over the Baltic Sea for one year using models and data-based methods. Tellus, 55A, 352-367.
  • Omstedt, A., Chen, Y. and K., Wesslander, (2005). A comparison between the ERA40 and the SMHI gridded meteorological databases as applied to Baltic Sea modelling. To appear in Nordic Hydrology, 36(4).
  • Rutgersson, A., Omstedt, A. and J., Räisänen (2002) Net precipitation over the Baltic Sea during present and future climate conditions. Climate Research, 22, 27-39.
  • Rutgersson, A., Omstedt, A. and Y., Chen, (2005). Evaluation of the heat balance components over the Baltic Sea using four gridded meteorological data bases and direct observations. To appear in Nordic Hydrology, 36(4).
  • Rutgersson, A. et al., 2005: The impact in models of including new results concerning sensible and latent heat fluxes over sea. In manuscript.
  • Sahlée E., A. Smedman, U. Högström and A. Rutgersson, (2005). Bulk exchange coefficient for humidity at sea during unstable and neutral conditions: Are-evaluation based on new field data. Submitted.
  • Smedman A.-S., Gryning, S-E., Bumke, K., Högström, U., Rutgersson, A., Batchvarova, E., Peters, G., Hennemuth, B., Tammelin, B., Hyvönen, R., Omstedt, A., Michelson, D., Andersson, T., and M., Clemens (2005a). Precipitation and evaporation Budgets over the Baltic proper: Observations and Modelling. Submitted.
  • Smedman A.-S., Högström,U., Sahlée, E. and C. Johansson, (2005b) Critical re-evaluation of the bulk transfer coefficient for sensible heat over the ocean during unstable and neutral conditions. Submitted.


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