The influence of air-sea coupling on forecasts of the 2016 Indian summer monsoon and its intraseasonal variability
The influence of air-sea coupling on forecasts of the 2016 Indian summer monsoon and its intraseasonal variability
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海气耦合对2016年印度夏季风预报的影响及其季节内变化
DOI：
10.1002/qj.3914
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发表时间：
2020
影响因子：
8.9
通讯作者：
Valdivieso M
中科院分区：
文献类型：
--
作者：
Valdivieso M
每日初始化的耦合和非耦合数值天气预报（NWP）预测从全球气象局统一模式（MetUM）进行比较，为2016年印度夏季风。使用了三种MetUM配置：仅大气（ATM），耦合到混合层海洋模式（KPP）和耦合到动力海洋模式（NEMO）。分析的重点是海气耦合的影响，特别是在孟加拉湾（BoB），季风降水数值预报。所有三种配置中的季节平均偏差高度一致，并由大气过程中的误差驱动。印度的降雨量最初被高估，但在BoB被低估，后者与太多的短波辐射和太少的云量有关。过量的短波辐射（BoB西北部的Wm − 2）部分被额外的潜热冷却所补偿，主要是由于高估了地面风速。在NEMO和KPP，耦合改善了印度的季节内活动和中断阶段的时间，主要是这些阶段的结束，这是系统性的太晚在ATM。NEMO和KPP表现出更现实的季节内局部相位关系的海表温度（SST）和降雨量在整个BoB，但没有配置再现所观察到的显着滞后的关系BoB SST和印度降雨。这种关系的缺乏可能部分归因于对北方BoB SST的弱热通量反馈，与卫星辐射相比，预测的短波反馈具有系统性的错误符号（正），因此有助于SST在所有提前时间变暖。基于这些MetUM预测，有一个有限的影响耦合NWP季风降雨，无论是平均降雨量和季节内变化。进一步的研究，以提高数值预报季风降雨应集中在减少MetUM大气系统偏差。
Daily initialized coupled and uncoupled numerical weather prediction (NWP) forecasts from the global Met Office Unified Model (MetUM) are compared for the 2016 Indian summer monsoon. Three MetUM configurations are used: atmosphere only (ATM), coupled to a mixed‐layer ocean model (KPP), and coupled to a dynamical ocean model (NEMO). The analysis focuses on the impact of air–sea coupling, particularly in the Bay of Bengal (BoB), on NWP for monsoon rainfall. Seasonal‐mean biases in all three configurations are highly consistent and driven by errors in atmospheric processes. Rainfall is initially overestimated over India, but underestimated over the BoB, the latter associated with too much short‐wave radiation and too little cloud cover in MetUM. The excess short‐wave radiation (Wm−2over the northwest BoB) is partially compensated by additional latent cooling, primarily due to overestimated surface wind speeds. In NEMO and KPP, coupling improves the timing of intraseasonal active and break phases over India, primarily the end of these phases, which are systematically too late in ATM. NEMO and KPP show a more realistic intraseasonal local phase relationship between sea surface temperature (SST) and rainfall throughout the BoB, but no configuration reproduces the observed significant lagged relationship between BoB SST and Indian rainfall. The lack of this relationship may be partly attributed to weak heat flux feedbacks to northern BoB SST, with the forecast short‐wave feedback having systematically the wrong sign (positive) compared to satellite radiation, and thus contributing to SST warming at all lead times. Based on these MetUM forecasts, there is a limited impact of coupling on NWP for monsoon rainfall, both for the mean rainfall and intraseasonal variability. Further research to improve NWP for monsoon rainfall should focus on reducing MetUM atmospheric systematical biases.