Pattern-based statistical downscaling of East Asian Summer Monsoon precipitation

Abstract

A B S T R A C TThis study identifies daily Meiyu-like East Asian Summer Monsoon patterns that are linked to precipitation observations in the Poyang lake catchment. This analysis provides insight into the dynamics of strong, local precipitation events and has the potential to improve projections of precipitation from coarse-grid numerical simulations. Precipitation observations between 1960 and 1999 are taken from 13 rain gauges located in the Poyang lake catchment, which is a sub-catchment of the Yangtze River. The analysis shows that the observations are linked to daily patterns of relative vorticity at 850 hPa (Vo850) and vertical velocity at 500 hPa (W500) taken from the ERA-40 re-analysis data set. The patterns are derived by two approaches: (a) empirical orthogonal function (EOF) analysis and (b) rotated EOF analysis. Vo850 and W500 refer to geostrophic and ageostrophic processes, respectively. A logistic regression connects the large-scale dynamics to the local observations, whereby a forward regression selects the patterns best suited as predictors for the probability of exceeding thresholds of 24 h accumulated rainfall at the gauges. The regression model is verified by cross-validation.The spatial structure of the detected patterns can be interpreted in terms of well-known meso-a-scale disturbances called Southwest vortices. Overall, the proposed EOF and rotated EOF patterns are both related to physical processes and have the potential to work as predictors for exceedance rates of local precipitation in the Poyang catchment.

Error analysis of upper tropospheric water vapor in CMIP5 models using “A-Train” satellite observations and reanalysis data

“…The seasonal variations are based on the monthly departures from the annual mean. Seasonal variations of UTWV are influenced by the seasonal cycle of temperature and large-scale circulation including the influence of monsoons (Polanski et al 2010;Simon et al 2013). Here, we use the vertical velocity at 500 hPa, ω 500 , to represent the influence of large-scale circulation.…”

Statistical downscaling and dynamical downscaling of regional climate in China: Present climate evaluations and future climate projections

“…Such statistical relationships between the regional-and large-scale climate variables must be calibrated before they are applied to make predictions for the research region [Fan et al, 2013;Salathe et al, 2007]. In the last 20 years a variety of statistical downscaling methods have been developed with a broad range of application in regional climate and climate change study in East Asia [Orlowsky et al, 2010;Simon et al, 2013]. These methods can be generally divided into three categories: analogs and weather typing, weather generators, and regressions [Gutiérrez et al, 2013].…”

Logistic Model as a Statistical Downscaling Approach for Forecasting a Wet or Dry Day in the Bagmati River Basin

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