Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 6681-6699, 2016
http://www.atmos-chem-phys.net/16/6681/2016/
doi:10.5194/acp-16-6681-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
02 Jun 2016
Representation of the tropical stratospheric zonal wind in global atmospheric reanalyses
Yoshio Kawatani1, Kevin Hamilton2, Kazuyuki Miyazaki1, Masatomo Fujiwara3, and James A. Anstey4 1Japan Agency for Marine-Earth Science and Technology, Yokohama, 236-0001, Japan
2International Pacific Research Center, University of Hawaii, Honolulu, 96822, USA
3Faculty of Environmental Earth Science, Hokkaido University, Sapporo, 060-0810, Japan
4Canadian Centre for Climate Modelling and Analysis, University of Victoria, Victoria, V8W 2Y2, Canada
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 easterly-to-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 (1979–2012). The SD among the reanalysis declines significantly over the record, although the geographical pattern of SD remains nearly constant.

Citation: Kawatani, Y., Hamilton, K., Miyazaki, K., Fujiwara, M., and Anstey, J. A.: Representation of the tropical stratospheric zonal wind in global atmospheric reanalyses, Atmos. Chem. Phys., 16, 6681-6699, doi:10.5194/acp-16-6681-2016, 2016.
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This paper compares the representation of the monthly-mean zonal wind in the equatorial stratosphere among major global atmospheric reanalysis data sets. Differences among reanalysis display a prominent equatorial maximum, indicating the particularly challenging nature of the reanalysis problem in the low-latitude stratosphere. Our study confirms that the high accuracy in situ wind measurements have provided important constraints to reanalyses of circulation in the tropical stratosphere.
This paper compares the representation of the monthly-mean zonal wind in the equatorial...
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