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

Abstract

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 d 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 middle atmospheric data assimilation. Second, the order of horizontal diffusion in the forecast model is changed 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.

Contribution of Gravity Waves to Universal Vertical Wavenumber (∼m−3) Spectra Revealed by a Gravity‐Wave‐Permitting General Circulation Model

“…A hindcast was performed from 5 December 2018 to 17 January 2019 using global analysis data produced by the JAGUAR-Data Assimilation System (JAGUAR-DAS) (Koshin et al, 2020(Koshin et al, , 2022 in a medium-resolution (T42L124) version of the JAGUAR as initial data. A four-dimensional local ensemble transform Kalman filter and a filter called incremental analysis updates (Bloom et al, 1996) are used in the JAGUAR-DAS.…”

Contribution of gravity waves to universal vertical wavenumber (~m^(-3)) spectra revealed by a gravity-wave-permitting general circulation model

“…A hindcast was performed for 5 December 2018 to 17 January 2019 using global analysis data produced by the JAGUAR-Data Assimilation System (JAGUAR-DAS) (Koshin et al, 2020(Koshin et al, , 2022 in a medium-resolution (T42L124) version of the JAGUAR as initial data. A four-dimensional local ensemble transform Kalman filter and a filter called incremental analysis updates (Bloom et al, 1996) are used in the JAGUAR-DAS.…”

A Comparison of Stratospheric Gravity Waves in a High-Resolution General Circulation Model with 3-D Satellite Observations

“…Hindcast simulations using JAGUAR were performed for boreal winter 2018-2019. The model was initialized by 3-day spectral nudging to a reanalysis dataset created by the JAGUAR-Data Assimilation System (JAGUAR-DAS; Koshin et al, 2020Koshin et al, , 2022. This nudging process relaxes only the low total horizontal wavenumber (𝑛) components of 𝑛= 0-15 to the reanalysis data, leaving GWs and other high n components (𝑛≥ 16) free to evolve.…”