Synoptic verification of medium-extended-range forecasts of the northwest pacific subtropical high and South Asian high based on multi-center TIGGE data

AbstractThe decadal intensification of the South Asian High (SAH) after the late 1970s, which is determined based on the geopotential height (H), is suspicious due to the lifting effect upon H caused by global warming. The updated reanalysis datasets of ERA5 and JRA55 indicate that the anticyclone in the upper troposphere over the Tibetan Plateau is relatively weak during 1980–2018 compared to that during 1950–1979. This decadal weakening of the SAH after 1979 can also be observed in the radiosonde observation data. Correspondingly, the SAH defined by eddy geopotential height (H’) reflects a consistent decadal weakening variation. The decadal weakening of SAH detected from H’ after the late 1970s matches with a decadal southward shift of the East Asian Westerly Jet, causing ascending motions over the Yangtze River Valley and descending motions over North China. Moreover, the decadal weakening and westward shift of the SAH is accompanied with the positive relative vorticity anomalies over the Northwest Pacific in the upper troposphere, which implies a declining and eastward shift of the western Pacific subtropical high (WPSH) and a weakened East Asian Summer Monsoon (EASM). Hence, the decadal weakening of the SAH after the late 1970s may contribute to the Yangtze-River-flooding-and-North-China-drought pattern through its connection with other circulation systems of EASM.

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Ensemble Empirical Mode Decomposition with Adaptive Noise with Convolution Based Gated Recurrent Neural Network: A New Deep Learning Model for South Asian High Intensity Forecasting

Symmetry ◽

10.3390/sym13060931 ◽

2021 ◽

Vol 13 (6) ◽

pp. 931

Author(s):

Kecheng Peng ◽

Xiaoqun Cao ◽

Bainian Liu ◽

Yanan Guo ◽

Wenlong Tian

Keyword(s):

Neural Network ◽

Time Series ◽

Deep Learning ◽

South Asian ◽

Recurrent Neural Network ◽

Ensemble Empirical Mode Decomposition ◽

South Asian High ◽

Mode Decomposition ◽

Adaptive Noise ◽

Deep Learning Model

The intensity variation of the South Asian high (SAH) plays an important role in the formation and extinction of many kinds of mesoscale systems, including tropical cyclones, southwest vortices in the Asian summer monsoon (ASM) region, and the precipitation in the whole Asia Europe region, and the SAH has a vortex symmetrical structure; its dynamic field also has the symmetry form. Not enough previous studies focus on the variation of SAH daily intensity. The purpose of this study is to establish a day-to-day prediction model of the SAH intensity, which can accurately predict not only the interannual variation but also the day-to-day variation of the SAH. Focusing on the summer period when the SAH is the strongest, this paper selects the geopotential height data between 1948 and 2020 from NCEP to construct the SAH intensity datasets. Compared with the classical deep learning methods of various kinds of efficient time series prediction model, we ultimately combine the Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) method, which has the ability to deal with the nonlinear and unstable single system, with the Permutation Entropy (PE) method, which can extract the SAH intensity feature of IMF decomposed by CEEMDAN, and the Convolution-based Gated Recurrent Neural Network (ConvGRU) model is used to train, test, and predict the intensity of the SAH. The prediction results show that the combination of CEEMDAN and ConvGRU can have a higher accuracy and more stable prediction ability than the traditional deep learning model. After removing the redundant features in the time series, the prediction accuracy of the SAH intensity is higher than that of the classical model, which proves that the method has good applicability for the prediction of nonlinear systems in the atmosphere.

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Connection between Anomalous Zonal Activities of the South Asian High and Eurasian Summer Climate Anomalies

Journal of Climate ◽

10.1175/jcli-d-15-0823.1 ◽

2016 ◽

Vol 29 (22) ◽

pp. 8249-8267 ◽

Cited By ~ 12

Author(s):

Jian Shi ◽

Weihong Qian

Keyword(s):

South Asian ◽

Surface Air Temperature ◽

Northern China ◽

Boreal Summer ◽

South Asian High ◽

The South ◽

Climate Anomalies ◽

Precipitation Anomalies ◽

Air Column ◽

Air Temperature Anomalies

Abstract Using the daily mean anomalies of atmospheric variables from the NCEP Reanalysis-1 (NCEP R1), this study reveals the connection between anomalous zonal activities of the South Asian high (SAH) and Eurasian climate anomalies in boreal summer. An analysis of variance identifies two major domains with larger geopotential height variability located in the eastern and western flanks of the SAH at around 100 and 150 hPa, respectively. For both eastern and western domains, extreme events are selected during 1981–2014 when normalized height anomalies are greater than 1.0 (less than −1.0) standard deviation for at least 10 consecutive days. Based on these events, four SAH modes that include strong and weak Tibetan modes (STM and WTM, respectively) and strong and weak Iranian modes (SIM and WIM, respectively) are defined to depict the zonal SAH features. The positive composite in the eastern (western) domain indicates the STM (SIM) manifests a robust wavelike pattern with an anomalous low at 150 hPa, and surface cold and wet anomalies over Mongolia and northern China (Kazakhstan and western Siberia) are surrounded by three anomalous highs at 150 hPa and surface warm and dry anomalies over Eurasia. Opposite distributions are also evident in the negative composites of the two domains (WTM and WIM). The surface air temperature anomalies are the downward extension of an anomalous air column aloft while the precipitation anomalies are directly associated with the height anomalies above the air column.

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Prediction of August Atlantic Basin Hurricane Activity

Weather and Forecasting ◽

10.1175/814.1 ◽

2004 ◽

Vol 19 (6) ◽

pp. 1044-1060 ◽

Cited By ~ 10

Author(s):

Eric S. Blake ◽

William M. Gray

Keyword(s):

Tropical Cyclone ◽

Subtropical High ◽

Northwest Pacific ◽

Seasonal Forecasts ◽

Reanalysis Dataset ◽

Atlantic Basin ◽

The North ◽

Hurricane Activity ◽

Environmental Prediction ◽

The Bering Sea

Abstract Although skillful seasonal hurricane forecasts for the Atlantic basin are now a reality, large gaps remain in our understanding of observed variations in the distribution of activity within the hurricane season. The month of August roughly spans the first third of the climatologically most active part of the season, but activity during the month is quite variable. This paper reports on an initial investigation into forecasting year-to-year variability of August tropical cyclone (TC) activity using the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis dataset. It is shown that 55%–75% of the variance of August TC activity can be hindcast using a combination of 4–5 global predictors chosen from a 12-predictor pool with each of the predictors showing precursor associations with TC activity. The most prominent predictive signal is the equatorial July 200-mb wind off the west coast of South America. When this wind is anomalously strong from the northeast during July, Atlantic TC activity in August is almost always enhanced. Other July conditions associated with active Augusts include a weak subtropical high in the North Atlantic, an enhanced subtropical high in the northwest Pacific, and low pressure in the Bering Sea region. The most important application of the August-only forecast is that predicted net tropical cyclone (NTC) activity in August has a significant relationship with the incidence of U.S. August TC landfall events. Better understanding of August-only TC variability will allow for a more complete perspective of total seasonal variability and, as such, assist in making better seasonal forecasts.

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Mapping users' expectations regarding extended-range forecasts

Advances in Science and Research ◽

10.5194/asr-15-99-2018 ◽

2018 ◽

Vol 15 ◽

pp. 99-106 ◽

Cited By ~ 2

Author(s):

Tiina Ervasti ◽

Hilppa Gregow ◽

Andrea Vajda ◽

Terhi K. Laurila ◽

Antti Mäkelä

Keyword(s):

Everyday Life ◽

Design Process ◽

General Public ◽

Online Survey ◽

Weather Conditions ◽

The Everyday ◽

Extended Range ◽

One Year ◽

Weather Risks ◽

Range Forecasts

Abstract. An online survey was used to map the needs and preferences of the Finnish general public concerning extended-range forecasts and their presentation. First analyses of the survey were used to guide the co-design process of novel extended-range forecasts to be developed and tested during the project. In addition, the survey was used to engage the respondents from the general public to participate in a one year piloting phase that started in June 2017. The respondents considered that the tailored extended-range forecasts would be beneficial in planning activities, preparing for the weather risks and scheduling the everyday life. The respondents also perceived the information about the impacts of weather conditions more important than advice on how to prepare for the impacts.

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