Abstract
The western North Pacific summer climate affects the densely populated East Asian countries, while seasonal forecasting over these regions remains challenging for dynamical models. This study evaluates the effect of the spring Indo-Pacific warm pool (IPWP) Hadley circulation on the forecast performance for summer western North Pacific (WNP) precipitation in the Met Office Global Seasonal Forecast System (GloSea5). GloSea5 skillfully predicts IPWP Hadley circulation, but has moderate forecast skill for summer WNP precipitation. Compared to observations, the significant relationship between the spring IPWP Hadley circulation and the summer WNP precipitation is overestimated in most hindcast members and in the ensemble mean. Furthermore, we confirmed that the forecast ensemble members with a stronger such regional circulation–precipitation relationship have better forecast performance for the summer WNP precipitation, suggesting the importance of such a relationship for the seasonal forecast of WNP precipitation. These results also imply the need to further investigate other important factors for the WNP precipitation, the effects of which may be suppressed by the overestimated regional circulation–precipitation relationship in GloSea5.
Highlights
The western North Pacific (WNP) witnesses frequent tropical cyclone activity and heavy rainfall in summer, which causes severe disasters in densely populated coastal regions (e.g. Mendelsohn et al 2012, Peduzzi et al 2012, Feng and Tsimplis 2014, Guo and Tan 2018a, 2018b)
Using 23 years of ensemble global seasonal hindcasts from the UK Met Office Global Seasonal Forecast System version 5 (GloSea5), we evaluated forecast performance for summer WNP precipitation and the effect of the relationship between spring Indo-Pacific warm pool (IPWP) Hadley circulation and summer WNP precipitation
GloSea5 produces a stronger-than-expected relationship between spring IPWP Hadley circulation and summer WNP precipitation, and it has moderate forecast skill for summer WNP precipitation
Summary
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Keywords: Hadley circulation, precipitation, western North Pacific, seasonal forecast Supplementary material for this article is available online Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
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