Assimilation for skin SST in the NASA GEOS atmospheric data assimilation system

Area of Science:

• Earth System Science
• Atmospheric Science
• Oceanography

Background:

• Current GEOS-5 Atmospheric Data Assimilation System (ADAS) uses prescribed sea surface temperature (SST) from OSTIA, equating SST and skin SST (Ts).
• This approach does not account for near-surface diurnal warming or cool-skin effects, limiting accuracy.

Purpose of the Study:

• To enhance the GEOS-5 ADAS by modeling and assimilating near-sea-surface infrared observations.
• To improve the representation of skin SST (Ts) within the GEOS atmospheric general circulation model (AGCM).

Main Methods:

• Modified the GEOS-ADAS Ts by incorporating modeling and assimilation of satellite infrared (IR) observations.
• Updated the GEOS AGCM atmosphere-ocean interface to include diurnal warming and cool-skin effects.
• Directly assimilated SST-relevant Advanced Very High Resolution Radiometer (AVHRR) radiance observations.

Main Results:

• Demonstrated improved assimilation of radiance observations beyond AVHRR's thermal IR bands, including hyperspectral sensors like AIRS and IASI.
• Achieved better agreement with in-situ buoy measurements of near-surface SST.
• Forecast skill scores showed marginal to neutral benefit from the modified Ts.

Conclusions:

• The developed enhancements improve the assimilation of satellite radiance data and in-situ SST measurements.
• The study advances the development of coupled atmosphere-ocean data assimilation systems.
• Further research may be needed to translate these assimilation improvements into significant forecast skill gains.