Abstracts for the 6th International GAME Conf.
3-5 December 2004
Kyoto Japan
Impact of soil moisture on interannual variability of boreal summer precipitation
Shinjiro Kanae (1), Yukiko Hirabayashi (2), Tomohito Yamada (3), Taikan Oki (3)
(1) Research Institute for Humanity and Nature, and University of Tokyo
(2) Yamanashi University
(3) IIS, University of Tokyo
A set of AGCM (CCSR/NIES AGCM) simulations for 1951-98 was carried out to investigate the influence of land surface hydrological conditions (soil moisture and snow) on interannual variability of boreal summer precipitation. It was achieved by the comparison between a simulation forced with observed SST and a simulation forced not only with observed SST but also with "realistic" land surface hydrological conditions which were produced in an offline land surface simulation of the corresponding years. The influence of the "realistic" land surface specification is evident in successful hindcast of interannual variability of precipitation over certain regions of the world: Sahel, central Asia, north of India, part of USA, middle of Australia and so on, mostly located in semi-arid regions. This is not unanticipated to scientists. These regions considerably correspond to regions where significant land-atmosphere coupling strength was found in previous studies (e.g. Koster et al., 2004, Science, in print), although the coupling strength was solely dependent on the internal dynamics of land-atmosphere system of AGCMs and it was difficult to compare with observed interannual variability. The validity of the coupling strength is, to a certain extent, demonstrated by this study which can compare with observation. These results imply that predictability of boreal summer precipitation exists over these certain regions if adequate land surface conditions are provided (to this AGCM and presumably to many current AGCMs). Another simulation forced with the same "realistic" land surface hydrological conditions but with a different initial condition of atmosphere was carried out to assess whether the good hindcast over the certain regions is reproducible. Comparison of simulated precipitation between two simulations both with the same prescribed land and ocean conditions exhibits that the precipitation variability over the certain regions is significantly reproducible. It is natural if considering reproducibility is necessarily required for predictability, and reproducible areas must limit predictable areas. However, in some regions like the Asian monsoon regions including oceans from Indian Ocean to the Western Pacific, we can broadly see the lack of success in the hindcast in spite of significant reproducibility. This mismatch may be a key to the improvement. In addition, it is recognized that the regions with significant reproducibility mostly exist just above tropical ocean, its adjacent land and semi-arid land areas where the forcing from underlying surface is large. There seems less (or almost no) reproducibility, and less (or almost no) predictability accordingly, in other parts of the world. Whether such a characteristic really represents a characteristic of real climate system should be further investigated using observation and reanalysis data for the improvement of prediction by AGCMs. One of the biggest motivations to conduct this study was the investigation on the snow-monsoon relationship. However, as is described above, the simulated interannual variability of boreal precipitation over Monsoon Asia rarely corresponds to that of observation. We need further basic studies on Asian monsoon modeling for clarifying the snow-monsoon relationship with AGCMs.
Submittal Information
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Research Institute for Humanity and Nature | |
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335 Takashima-cho, Kamigyo-ku, Kyoto 602-0878 | |
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