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Titel |
The diabatic heat budget of the upper troposphere and stratosphere in ECMWF ERA-40 and ERA-Interim reanalyses |
VerfasserIn |
S. Fueglistaler, B. Legras, A. Beljaars, J.-J. Morcrette, A. Simmons, A. M. Tompkins, S. Uppala |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250025952
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Zusammenfassung |
We present an analysis of the diabatic terms in the thermodynamic energy equation from
ERA-40 and the ECMWF reanalysis ERA-Interim. We analyse the clear sky radiative
heating, the cloud radiative effects, and the impact from latent heat exchange and mixing. The
diabatic heat budget is closed with the calculation of the temperature assimilation increment.
The previously noted excessive tropospheric circulation at low latitudes in ERA-40 is also
reflected in the diabatic heat budget. The temperature increment acts to cool the excessive
model heating. Conversely, ERA-Interim requires heating from the assimilation increment at
low latitudes, suggesting too little convection. In the tropical tropopause layer (TTL), both
reanalyses show a strong heating from the interaction of clouds with radiation, but lack of
reliable independent estimates renders the role of clouds uncertain. Both reanalyses show
cooling in the TTL by the assimilation increment, suggesting that the models may
overestimate the cloud radiative heating, or that the convective parameterization scheme has
difficulties to capture the thermal effects of deep convection. In the stratosphere, ERA-40
shows unrealistic radiative heating due to problems in the temperature profile. The
diabatic heat balance is dominated by the the assimilation increment, and the residual
circulation is much faster than in ERA-Interim. Conversely, ERA-Interim is better
balanced and requires a substantially smaller temperature increment. Its structure and
magnitude of radiative heating/cooling at low/high latitudes is quite realistic. Overall,
ERA-Interim provides a much improved residual circulation, but uncertainties in
the magnitude of terms in particular around the tropical tropopause remain large. |
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