Preprints
https://doi.org/10.5194/gmd-2020-381
https://doi.org/10.5194/gmd-2020-381

Submitted as: development and technical paper 16 Mar 2021

Submitted as: development and technical paper | 16 Mar 2021

Review status: this preprint is currently under review for the journal GMD.

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

Dai Koshin1, Kaoru Sato1, Masashi Kohma1, and Shingo Watanabe2 Dai Koshin et al.
  • 1Department of Earth Planetary Science, The University of Tokyo, Tokyo,1130033, Japan
  • 2Japan Agency for Marine-Earth Science and Technology, Yokohama, 2360001, Japan

Abstract. 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 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) 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.

Dai Koshin et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2020-381', Anonymous Referee #1, 18 Jun 2021 reply
    • AC1: 'Reply on RC1', Dai Koshin, 29 Jun 2021 reply

Dai Koshin et al.

Data sets

NCEP ADP Global Upper Air and Surface Weather Observations (PREPBUFR format) National Centers for Environmental Prediction/National Weather Service/NOAA/U.S. Department of Commerce https://doi.org/10.5065/Z83F-N512

Aura MLS data GES DISC https://doi.org/10.5067/Aura/MLS/DATA2021

Dai Koshin et al.

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Short summary
The 4-D ensemble Kalman filter data assimilation system for the whole neutral atmosphere has been updated. The update includes the introduction of a filter to reduce the generation of spurious waves, modification of the horizontal diffusion of the forecast model to reproduce more realistic tidal amplitudes, and use of additional satellite observations. As a result, the analysis performance has been greatly improved, even for disturbances with periods of less than one day.