JRA-55: Notes, Questions, and Discussion

Hi, Sir,

From previous comments, I konw Brightness temperature is the SST, but I'd like to know if the SST over Arctic and Antarctica are the water temperature or sea ice temperature, the trend is so different when I compare the monthly time series of SST for ERA5 and JRA55 over Arctic and Antarctica, as I understand the SST in EAR5 is for water temperature. Would you mind provide some references? Thank you for your help, I really appreciate.

best,

nenghan

Dear All:

Are there any papers that evaluate upper tropospheric wind field (~200hPa wind) for ERA-Interim, ERA5, and JRA55?

Many Thanks.

Regards,

Aaron

Dear All:

Sorry, I made a mistake in the previous post.

I don't understand why JRA55's resolution is ~55km. If it uses T319 spectral model, isn't the horizontal resolution=[earth circumference]/[320*2]=40000km/640=62.5km.

Thanks,

Aaron

Brightness temperature is actually SST. This SST comes from the COBE daily data, but is not exactly the same because it includes a parameterized diurnal cycle. So it differs from the COBE data in terms of the temporal variability as well as the resolution.

This brightness temperature is computed from surface upward longwave radiation assuming that the surface is a black body. As long as this assumption is valid, the brightness temperature can be used as skin temperature as well.

Hi, I need to know what variables (T, UV winds, surface pressure, etc.) JRA55 assimilates from land met stations and moored buoy arrays such as TAO, TRITON and RAMA. I saw on this forum that it doesn't assimilate winds from land met stations, if I understood correctly.

Also, does JRA55 assimilates any variables measured by moored buoys offshore the Spanish Atlantic coast, operated by the Spanish Agency Puertos del Estado?

Any help would be much appreciated, thanks!

Users should be aware that for 2mT, 2mq, 10m u and v and some others, that they should use the "forecast" variable and not the "analysis" variable. The WRIT pages now have both.

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Table 5 and section 3.2a "screen level analysis" of

Kobayashi, S., Y. Ota, Y. Harada, A. Ebita, M. Moriya, H. Onoda, K. Onogi, H. Kamahori, C. Kobayashi, H. Endo, K. Miyaoka, and K. Takahashi , 2015: The JRA-55 Reanalysis: General Specifications and Basic Characteristics. J. Meteorol. Soc. Japan, 93, 5-48, doi: 10.2151/jmsj.2015-001

describes the details of this "separate" analysis:

The analysis of screen-level variables (2-m temperatures, 2-m relative humidities and 10-m winds) is performed separately from the atmospheric analysis component. These variables are analyzed with a univariate 2-dimensional optimal interpolation (2D-OI). In JRA-25, departures were estimated by comparing observations with the first guess at the analysis time. In JRA-55, observations are compared with the first guess at the actual observation time and the departures are applied at the analysis time (the so-called first guess at the appropriate time (FGAT) approach). Temperature and wind observations from islands are not used because they are not necessarily representative at the grid scale of JRA-55. Determining whether an observation is from an island is based on the 0.25-degree resolution land cover data; consequently, observations from the coast are also excluded. Screen-level analysis fields are not used as initial conditions for forecasts.