EGU General Assembly 2021
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

An update on the 4D-LETKF data assimilation system for the wholeneutral atmosphere 

Dai Koshin1, Kaoru Sato1, Masashi Kohma1, and Shingo Watanabe2
Dai Koshin et al.
  • 1Department of Earth Planetary Science, The University of Tokyo, Tokyo, Japan (
  • 2Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan

The four-dimensional local ensemble transform Kalman filter (4D-LETKF) data assimilation system for the whole
neutral atmosphere is updated to better represent disturbances with wave periods shorter than 1 day in the mesosphere and
10 lower thermosphere (MLT) region. First, incremental analysis update (IAU) filtering is introduced to reduce the generation
of spurious waves arising from the insertion of the analysis updates. The IAU is better than other filtering methods, and also
is commonly used for the middle atmospheric data assimilation. Second, the horizontal diffusion in the forecast model is
modified to reproduce the more realistic tidal amplitudes that were observed by satellites. Third, the Sounding of the
Atmosphere using Broadband Emission Radiometry (SABER) and Special Sensor Microwave Imager/Sounder (SSMIS)
15 observations in the stratosphere and mesosphere also are assimilated. The performance of the resultant analyses is evaluated
by comparing them with the mesospheric winds from meteor radars, which are not assimilated. The representation of
assimilation products is greatly improved not only for the zonal mean field but also for short-period and/or horizontally
small-scale disturbances. 

How to cite: Koshin, D., Sato, K., Kohma, M., and Watanabe, S.: An update on the 4D-LETKF data assimilation system for the wholeneutral atmosphere , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13005,, 2021.

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