[A-AS07] Weather, Climate, and Environmental Science Studies using High-Performance Computing

[AAS07-08] Quality assessment of the third Japanese Reanalysis for Three Quarters of a Century (JRA-3Q) during a pre-satellite era

*Hiroaki Naoe¹, Shinya Kobayashi², Yuki Kosaka², Jotaro Chiba², Takayuki Tokuhiro², Yayoi Harada¹ (1.Meteorological Research Institute / Japan Meteorological Agency, 2.Office of Earth System Modeling / Numerical Prediction Division / Japan Meteorological Agency)

Keywords:Long-term Reanalysis , JRA-3Q, quality assessment of a pre-satellite era

This study evaluates the latest Japanese Reanalysis for Three Quarters of a Century (JRA-3Q) conducted by the Japan Meteorological Agency (JMA), focusing on a semi-period of pre-satellite era (1960s and 1970s). JRA-3Q is the third Japanese global atmospheric reanalysis covering the period from late 1940s onward, and it is based on the JMA's operational system as of December 2018. The atmospheric model has a TL479 horizontal resolution and 100 vertical layers up to 0.01 hPa, and the core component of the JRA-3Q data assimilation system is the 6-hourly 4D-Var of the atmospheric state with a T319-resolution inner model. Three-dimensional daily-mean ozone distributions used in JRA-3Q were calculated using an off-line ozone transport model (MRI-CCM2, TL159L64) with a nudging scheme to assimilate Level 3 total column ozone (TCO) datasets which had originally produced from Level 2 TCO datasets for the period after 1979, and without a TCO nudging but bias-corrected for the period before 1978.
Because there are only few global-covered observational datasets during the pre-satellite era, evaluation of the JRA-3Q is mainly to conduct an intercomparison of other reanalysis datasets such as representation Japanese 55-year Reanalysis (JRA-55), a JRA-55's subset of atmospheric reanalysis assimilating conventional observations only (JRA-55C), and version 3 of the Twentieth Century Reanalysis (20CRv3), and also an intercomparison of JRA-3Q between the pre-satellite and satellite eras. Emphasis of this evaluation during the non-satellite era is placed on the representation of tropical circulation, the consistency in time of the reanalysed fields, detection of tropical cyclones, and the quality of the stratospheric water vapour and ozone. For example, the surface circulation over the tropical Africa is improved by means of reducing spurious anticyclonic circulation anomalies that were found in JRA-55. Stratospheric ozone is improved by the use of adequate ozone depletion substances, sea-surface temperature, and so on as well as the improvements of the ozone model. Although the atmospheric model can produce self-generated quasi-biennial oscillation (QBO) by introducing non-orographic gravity wave drag, the evaluation reveals that JRA-3Q has a shorter period of around one year in the middle stratosphere and diminished QBO amplitude in the lower stratosphere, indicating that representation of the QBO in JRA-3Q is not as good as that in JRA-55.