ACCESS-S2 seasonal forecasts of rainfall and the SAM–rainfall relationship during the grain growing season in south-west Western Australia

IF 3.6 4区 地球科学 Q1 Earth and Planetary Sciences
Rebecca Firth, Jatin Kala, Debra Hudson, Kerryn Hawke, Andrew Marshall
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Abstract

South-west Western Australia (SWWA) is home to a world class grains industry that is significantly affected by periods of drought. Previous research has shown a link between the Southern Annular Mode (SAM) and rainfall in SWWA, especially during winter months. Hence, the predictability of the SAM and its relationship to SWWA rainfall can potentially improve forecasts of SWWA drought, which would provide valuable information for farmers. In this paper, focusing on the 0-month lead time forecast, we assess the bias and skill of ACCESS-S2, the Australian Bureau of Meteorology’s current operational sub-seasonal to seasonal forecasting system, in simulating seasonal rainfall for SWWA during the growing season (May–October). We then analyse the relationship between the SAM and SWWA precipitation and how well this is captured in ACCESS-S2 as well as how well ACCESS-S2 forecasts the monthly SAM index. Finally, ACCESS-S2 rainfall forecasts and the simulation of SAM are assessed for a case study of extreme drought in 2010. Our results show that forecasts tend to have greater skill in the earlier part of the season (May–July). ACCESS-S2 captures the significant inverse SAM–rainfall relationship but underestimates its strength. The model also shows overall skill in forecasting the monthly SAM index and simulating the MSLP and 850-hPa wind anomaly patterns associated with positive and negative SAM phases. However, for the 2010 drought case study, ACCESS-S2 does not indicate strong likelihoods of the upcoming dry conditions, particularly for later in the growing season, despite predicting a positive (although weaker than observed) SAM index. Although ACCESS-S2 is shown to skillfully depict the SAM–SWWA rainfall relationship and generally forecast the SAM index well, the seasonal rainfall forecasts still show limited skill. Hence it is likely that model errors unrelated to the SAM are contributing to limited skill in seasonal rainfall forecasts for SWWA, as well as the generally low seasonal-timescale predictability for the region.

ACCESS-S2 对西澳大利亚西南部谷物生长季节的降雨量和 SAM 与降雨量之间关系的季节性预测
西澳大利亚西南部(SWWA)拥有世界一流的谷物产业,该产业受到干旱期的严重影响。先前的研究表明,南环流模式(SAM)与西澳大利亚西南部的降雨量之间存在联系,尤其是在冬季。因此,南环流模式的可预测性及其与西南地区降雨量的关系有可能改善西南地区的干旱预报,从而为农民提供有价值的信息。在本文中,我们以 0 个月提前期预报为重点,评估了澳大利亚气象局目前运行的分季节到季节预报系统 ACCESS-S2 在模拟西南地区生长季节(5 月至 10 月)季节性降雨时的偏差和技能。然后,我们分析了 SAM 与 SWWA 降水量之间的关系,以及 ACCESS-S2 对这种关系的捕捉程度和 ACCESS-S2 对每月 SAM 指数的预报程度。最后,ACCESS-S2 降水预报和 SAM 模拟在 2010 年极端干旱的案例研究中进行了评估。我们的结果表明,在季节的早期(5 月至 7 月),预测往往具有更高的技能。ACCESS-S2 模型捕捉到了 SAM 与降雨量之间的显著反比关系,但低估了这种关系的强度。该模式在预报月 SAM 指数以及模拟与正负 SAM 阶段相关的 MSLP 和 850 hPa 风异常模式方面也显示出整体技能。然而,在 2010 年干旱案例研究中,尽管 ACCESS-S2 预测了正的 SAM 指数(尽管比观测到的要弱),但并没有显示出即将出现干旱状况的强烈可能性,尤其是在生长季节的后期。尽管 ACCESS-S2 可以熟练地描绘 SAM-SWWA 降雨量关系,并对 SAM 指数进行良好的预测,但对季节性降雨量的预测仍然显示出有限的技能。因此,可能是与 SAM 无关的模式误差导致了西南地区季节性降雨预报的有限技能,以及该地区普遍较低的季节-时间尺度可预测性。
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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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