Preliminary Results of the JRA-55C, an Atmospheric Reanalysis Assimilating Conventional Observations Only

Kobayashi, Chiaki; Endo, Hirokazu; Ota, Yukinari; Kobayashi, Shinya; Onoda, Hirokatsu; Harada, Yusuke; Onogi, Kazutoshi; Kamahori, Hirotaka

doi:10.2151/sola.2014-016

Cited by 71 publications

(84 citation statements)

References 9 publications

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“…The effects of satellite data sets might be investigated by comparison between JRA-55 and JRA-55c (which excludes all satellite data as input). Kobayashi et al (2014) compare the JRA-55 and JRA-55C reanalyses and indicate that the tropical zonal wind difference between the JRA-55 and JRA-55C is large in the upper stratosphere compared to that in the lower stratosphere, and the amplitude in JRA-55C is smaller than that of the JRA-55. More detail comparisons along these lines are reserved for future work.…”

Section: Summary and Concluding Remarksmentioning

confidence: 91%

Representation of the tropical stratospheric zonal wind in global atmospheric reanalyses

et al. 2016

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Abstract. This paper reports on a project to compare the representation of the monthly-mean zonal wind in the equatorial stratosphere among major global atmospheric reanalysis data sets. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly-mean zonal wind and this depends on latitude, longitude, height, and the phase of the quasi-biennial oscillation (QBO). At each height the SD displays a prominent equatorial maximum, indicating the particularly challenging nature of the reanalysis problem in the low-latitude stratosphere. At 50-70 hPa the geographical distributions of SD are closely related to the density of radiosonde observations. The largest SD values are over the central Pacific, where few in situ observations are available. At 10-20 hPa the spread among the reanalyses and differences with in situ observations both depend significantly on the QBO phase. Notably the easterly-to-westerly phase transitions in all the reanalyses except MERRA are delayed relative to those directly observed in Singapore. In addition, the timing of the easterlyto-westerly phase transitions displays considerable variability among the different reanalyses and this spread is much larger than for the timing of the westerly-to-easterly phase changes. The eddy component in the monthly-mean zonal wind near the Equator is dominated by zonal wavenumber 1 and 2 quasi-stationary planetary waves propagating from midlatitudes in the westerly phase of the QBO. There generally is considerable disagreement among the reanalyses in the details of the quasi-stationary waves near the Equator. At each level, there is a tendency for the agreement to be best near the longitude of Singapore, suggesting that the Singapore observations act as a strong constraint on all the reanalyses. Our measures of the quality of the reanalysis clearly show systematic improvement over the period considered . The SD among the reanalysis declines significantly over the record, although the geographical pattern of SD remains nearly constant.

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Section: Summary and Concluding Remarksmentioning

confidence: 91%

Representation of the tropical stratospheric zonal wind in global atmospheric reanalyses

et al. 2016

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“…We use the fields on the model grid and vertical levels, which has a resolution of ∼ 1 km in the UTLS. A reanalysis, JRA-55C, using the same assimilation system as for JRA-55, but with only "conventional" data inputs (that is, no satellite data), was run for 1972 through 2012 (Kobayashi et al, 2014;Fujiwara et al, 2017). In Sect.…”

Section: Jra-55mentioning

confidence: 99%

“…Several of the reanalysis centers have produced "conventional data only" (i.e., no satellite data inputs) reanalyses (for an overview, see Fujiwara et al, 2017). The JMA's JRA-55C is such a reanalysis for 1972 through 2012 using the same model and assimilation system as for JRA-55 (Kobayashi et al, 2014). To elucidate the impact of including satellite data in the assimilation during the period since 1979 that we study here (often referred to as the satellite era), Figures 5 and 6 show the JRA-55-JRA-55C differences for June-JulyAugust (JJA; again, the season is chosen to show the most characteristic behavior).…”

Section: Grid Output Product and Assimilated Field Choicesmentioning

confidence: 99%

Reanalysis comparisons of upper tropospheric–lower stratospheric jets and multiple tropopauses

et al. 2017

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Abstract. The representation of upper tropospheric–lower stratospheric (UTLS) jet and tropopause characteristics is compared in five modern high-resolution reanalyses for 1980 through 2014. Climatologies of upper tropospheric jet, subvortex jet (the lowermost part of the stratospheric vortex), and multiple tropopause frequency distributions in MERRA (Modern-Era Retrospective analysis for Research and Applications), ERA-I (ERA-Interim; the European Centre for Medium-Range Weather Forecasts, ECMWF, interim reanalysis), JRA-55 (the Japanese 55-year Reanalysis), and CFSR (the Climate Forecast System Reanalysis) are compared with those in MERRA-2. Differences between alternate products from individual reanalysis systems are assessed; in particular, a comparison of CFSR data on model and pressure levels highlights the importance of vertical grid spacing. Most of the differences in distributions of UTLS jets and multiple tropopauses are consistent with the differences in assimilation model grids and resolution – for example, ERA-I (with coarsest native horizontal resolution) typically shows a significant low bias in upper tropospheric jets with respect to MERRA-2, and JRA-55 (the Japanese 55-year Reanalysis) a more modest one, while CFSR (with finest native horizontal resolution) shows a high bias with respect to MERRA-2 in both upper tropospheric jets and multiple tropopauses. Vertical temperature structure and grid spacing are especially important for multiple tropopause characterizations. Substantial differences between MERRA and MERRA-2 are seen in mid- to high-latitude Southern Hemisphere (SH) winter upper tropospheric jets and multiple tropopauses as well as in the upper tropospheric jets associated with tropical circulations during the solstice seasons; some of the largest differences from the other reanalyses are seen in the same times and places. Very good qualitative agreement among the reanalyses is seen between the large-scale climatological features in UTLS jet and multiple tropopause distributions. Quantitative differences may, however, have important consequences for transport and variability studies. Our results highlight the importance of considering reanalyses differences in UTLS studies, especially in relation to resolution and model grids; this is particularly critical when using high-resolution reanalyses as an observational reference for evaluating global chemistry–climate models.

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“…The model specification, data assimilation system and input observations for the JRA-55CHS are the same as those used for the "JRA-55 Conventional" (JRA-55C; Kobayashi et al 2014) except for SST specification. The horizontal resolution of the forecast model is TL319 (equivalent to ~55km resolution) with 60 sigma-pressure hybrid vertical levels.…”

Section: Outline Of Jra-55chs and Satellite Observations For Verificamentioning

confidence: 99%

JRA-55CHS: An Atmospheric Reanalysis Produced with High-Resolution SST

Masunaga

Nakamura

Kamahori

et al. 2018

SOLA

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As an additional product of the Japanese 55-year Reanalysis (JRA-55) project, a new global atmospheric reanalysis product, named JRA-55CHS, is under construction. It utilizes quarterdegree sea-surface temperature (SST) as lower-boundary condition with the same data assimilation system as the JRA-55 Conventional (JRA-55C), into which no satellite data is assimilated. The SST data can resolve steep SST gradients along the western boundary currents (WBCs), which are not necessarily well represented in many of the other atmospheric reanalysis products, including the JRA-55C. The present paper briefly documents basic performance of the JRA-55CHS, through comparing it with the JRA-55C and satellite observations in focusing on the major WBC regions. In the JRA-55CHS, mesoscale atmospheric structures along the WBCs are well reproduced in their climatological-mean fields as captured in the satellite observations. Their interannualto decadal-scale variations associated with SST variations are also reasonably reproduced. The corresponding atmospheric features are less obvious in the JRA-55C owing to smoother SST prescribed. Furthermore, comparison between the two reanalysis products reveals that the influence of frontal-scale SST distributions can reach into the middle and upper troposphere, especially in summer. The JRA-55CHS will be useful for deepening our understanding of the nature of midlatitude frontal-scale air-sea interactions.

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Preliminary Results of the JRA-55C, an Atmospheric Reanalysis Assimilating Conventional Observations Only

Cited by 71 publications

References 9 publications

Representation of the tropical stratospheric zonal wind in global atmospheric reanalyses

Representation of the tropical stratospheric zonal wind in global atmospheric reanalyses

Reanalysis comparisons of upper tropospheric–lower stratospheric jets and multiple tropopauses

JRA-55CHS: An Atmospheric Reanalysis Produced with High-Resolution SST

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