9 December 2022
Information Infrastructure Department
Japan Meteorological Agency

JRA-3Q UsageLocal issues with sea ice parameters
Outline
The Japanese Reanalysis for Three Quarters of a Century (JRA-3Q) contained errors in ice cover for theperiod from June 1985 to April 2013. As a result, values within around 250 km surrounding the relevant area(with coverage of 0.1 or above), which should be 0.0, is reported as an average of 0.15. However, the differenceis only a fraction of the standard deviation in year-to-year variation, and effects on JRA-3Q quality are localand minor.

Cause
In this processing, values for ice cover analysis in the 0.25-degree latitude/longitude grid (horizontalresolution: approx. 25 km) for June 1985 onward were converted to the forecast model grid system (horizontalresolution: approx. 40 km) and used as lower boundary conditions. To prevent unintended open-ice areas incoastal areas due to differences in land-sea distribution between the two systems, sea ice areas were expanded
by several grids before the system transformation. For ice cover from June 1985 to April 2013, this treatment(used only for coastal areas) was also applied to sea ice in open-ocean areas.

Effects
Table 1 shows the related period and relevant parameters. Figures 1 to 4 show differences between pre-/posterror experiments conducted to evaluate effects for February 2017 (the Northern Hemisphere sea ice maximumperiod). The area within around 250 km of the sea ice area averages approximately 0.15, where ice cover shouldbe 0.0. Other effects include increased surface upward short-wave radiation flux, reduced surface upward longwave radiation and sensible/latent heat fluxes, reduced 2-m temperature and increased 2-m relative humidity.
These differences represent only a fraction of standard deviation in year-to-year variation, but should be noted
in reference to sea ice data for this period.
There are no errors in grid system data outside June 1985 to April 2013.

1

Table 1 Quality issues relating to sea-ice errors
PeriodJune 1985 to April 2013
(Around sea ice areas)

Parameters2



Ice coverSurface upward short-wave radiation fluxSurface upward long-wave radiation flux

Sensible/latent heat fluxes

Surface temperature/relative humidity

(a) Error-uncorrected(b) Error-corrected(c) Error-uncorrected – Error-corrected

Fig. 1 Effects of incorrect ice-cover handling for the Northern Hemisphere (1)Ice cover (proportions) for February 15, 2017. The red line in (a) indicates erroneous sea ice spread. Since thevalue of the adjacent grid is used, the average is around 0.15.
(a) Ice cover (proportion)(b) Surface upward short-wave radiation (W m-2) (c) Surface upward long-wave radiation (W m-2)(d) Sensible heat flux (W m-2)(e) Latent heat flux (W m-2)(g) 2-m relative humidity analysis (%)(h) Temperature analysis at 850 hPa (K)(f) 2-m temperature analysis (K)Fig. 2 Effects of incorrect ice-cover handling for the Northern Hemisphere (2)Monthly mean differences between incorrect and correct handling of ice cover for February 20173

(a) Error-uncorrected(b) Error-corrected(c) Error-uncorrected - Error-corrected

Fig. 3 Effects of incorrect ice-cover handling for the Southern Hemisphere (1)Ice cover (proportions) for February 15, 2017. The red line in (a) indicates erroneous sea spread. Since thevalue of the adjacent grid is used, the average is around 0.15.
(a) Ice cover (proportion)(b) Surface upward short-wave radiation (W m-2) (c) Surface upward long-wave radiation (W m-2)(d) Sensible heat flux (W m-2)(e) Latent heat flux (W m-2)(g) 2-m relative humidity analysis (%)(h) Temperature analysis at 850 hPa (K)(f) 2-m temperature analysis (K)Fig. 4 Effects of incorrect ice-cover handling for the Southern Hemisphere (2)Monthly mean differences between incorrect and correct handling of ice cover for February 20174