Observing and forecasting the retreat of northern Australia’s rainy season

IF 3.6 4区 地球科学 Q1 Earth and Planetary Sciences
Tim Cowan, Emily Hinds, Andrew G. Marshall, Matthew C. Wheeler, Catherine de Burgh-Day
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引用次数: 0

Abstract

According to the Australian Bureau of Meteorology, the northern Australian wet season extends through to April, which also formally marks the end of Australia’s tropical cyclone season. Mid-autumn is when the tropical dry season transition period begins, when crop farmers prepare land for annual crops or pasture–fodder harvest, or when beef cattle producers make decisions regarding stock numbers and feed rationing. Potentially knowing if the last rains of the wet season will be later or earlier than normal would be valuable information for northern sectors such as agriculture, infrastructure and tourism. The Bureau of Meteorology provides seasonal forecasts of the Northern Rainfall Onset – the date when a location has accumulated 50 mm of rain from 1 September – yet there is currently no prediction of the rainy season retreat (the Northern Rainfall Retreat, NRR). In this study, we draw on three different NRR definitions and investigate how they vary with the El Niño–Southern Oscillation and the Madden–Julian Oscillation (MJO). In general, retreats occur ~1 week later than normal across the far northern tropics following La Niña events, but little change from normal occurs for El Niño. Although most retreats occur when the MJO is weak, if the MJO is active, retreats are mostly observed in phases 6 and 7, when convection is passing through the western Pacific. Utilising the Bureau of Meteorology’s sub-seasonal to seasonal forecast system, ACCESS-S2, we show that the model has some skill in forecasting the NRR across the far northern regions at a lead time of ~2.5 months, but poor skill in the subtropics and arid locations. Verification of the 2023 NRR forecasts, highlights the challenges of predicting the timing and magnitude of daily rainfall at such a long lead time.

观测和预测澳大利亚北部雨季的消退
根据澳大利亚气象局的数据,澳大利亚北部的雨季一直持续到四月,这也正式标志着澳大利亚热带气旋季节的结束。仲秋时节是热带旱季的过渡时期,也是农作物种植者为收获一年生作物或牧草饲料而整地的时节,还是肉牛生产者就存栏数量和饲料配给做出决定的时节。如果能知道雨季的最后一场降雨是晚于还是早于正常时间,对北方的农业、基础设施和旅游业等部门来说将是非常有价值的信息。气象局提供了北部降雨开始的季节性预报--即从 9 月 1 日起某地累计降雨量达到 50 毫米的日期,但目前还没有雨季消退(北部降雨消退,NRR)的预报。在本研究中,我们借鉴了三种不同的 NRR 定义,并研究了它们如何随厄尔尼诺-南方涛动和麦登-朱利安涛动(MJO)而变化。一般来说,在拉尼娜现象发生后,远北热带地区的退缩比正常情况晚 1 周左右,但在厄尔尼诺现象发生时,与正常情况相比变化不大。虽然大多数回缩发生在 MJO 较弱的时候,但如果 MJO 活跃,回缩大多发生在第 6 和第 7 阶段,此时对流正在穿过西太平洋。利用气象局的分季节到季节预报系统 ACCESS-S2,我们发现该模式在预报远北地区的 NRR 时,在约 2.5 个月的提前期有一定的预报能力,但在亚热带和干旱地区预报能力较差。对 2023 年 NRR 预报的验证凸显了在如此长的准备时间内预测每日降雨时间和降雨量所面临的挑战。
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来源期刊
Journal of Southern Hemisphere Earth Systems Science
Journal of Southern Hemisphere Earth Systems Science Earth and Planetary Sciences-Oceanography
CiteScore
8.10
自引率
8.30%
发文量
0
审稿时长
>12 weeks
期刊介绍: The Journal of Southern Hemisphere Earth Systems Science (JSHESS) publishes broad areas of research with a distinct emphasis on the Southern Hemisphere. The scope of the Journal encompasses the study of the mean state, variability and change of the atmosphere, oceans, and land surface, including the cryosphere, from hemispheric to regional scales. general circulation of the atmosphere and oceans, climate change and variability , climate impacts, climate modelling , past change in the climate system including palaeoclimate variability, atmospheric dynamics, synoptic meteorology, mesoscale meteorology and severe weather, tropical meteorology, observation systems, remote sensing of atmospheric, oceanic and land surface processes, weather, climate and ocean prediction, atmospheric and oceanic composition and chemistry, physical oceanography, air‐sea interactions, coastal zone processes, hydrology, cryosphere‐atmosphere interactions, land surface‐atmosphere interactions, space weather, including impacts and mitigation on technology, ionospheric, magnetospheric, auroral and space physics, data assimilation applied to the above subject areas . Authors are encouraged to contact the Editor for specific advice on whether the subject matter of a proposed submission is appropriate for the Journal of Southern Hemisphere Earth Systems Science.
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