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This study utilizes satellite-based rainfall CHIRPS to evaluate GCMs-CMIP6 models over Sudan from 1985 to 2014. Overall, the GCMs of BCC-CSM2-MR, CAMS-CSM1-0, CESM2, ECEarth3-Veg, GFDL-ESM4, MIROC-ES2L, and NorESM2-MM are well reproduced in the unimodal pattern of June to September (JJAS), and hence employed to calculate Multi-Model Ensemble (MME). Then, we examine the capability of the GCMs and MME in replicating the precipitation patterns on annual and seasonal scales over Sudan using numerous ranking metrics, including Pearson Correlation Coefficient (CC), Standard Deviation (SD), Taylor Skill Score (TSS), Mean Absolute Error (MAE), absolute bias (BIAS), and, normalized mean root square error (RMSD). The results show that the MME has the lowest bias and slightly overestimates rainfall over most parts of our study domain, whilst, others (ACCESS-CM2, BCC-CSM2-MR, CAMS-CSM1-0, CESM2, CNRM-CM6-1, CNRM-CM6-1-HR, CNRM-ESM2-1, FGOALS-f3-L, FGOALS-g3) consistently overestimate rainfall in referring to CHIRPS data, respectively, but FIO-ESM-2-0 underestimates bias value. Moreover, MIROC-ES2L and NorESM2-MM demonstrate better performance than the other models. Finally, we employed a bias correction (BC) technique, namely Delta BC, to adjust the GCMs model products through the annual and monsoon seasons. The applied bias correction technique revealed remarkable improvement in the GCMs against the observations, with an improvement of 0 - 18% over the original. However, MME and MIROC-ES2L show better performance after correction than other models. [ABSTRACT FROM AUTHOR]

The study investigates the influence of the tropical Atlantic Ocean and its Walker circulation cell on October–December (OND) rainfall variability over Tanzania. The first two SVD modes contribute 95.3% of the total covariance with the strongest (positive) and significant correlation (r ≅.7) at the 99% confidence level showing a close relationship between OND rainfall and MAM tropical Atlantic SST anomalies. Significant positive running correlation observed between MAM Atlantic SSTs and OND rainfall indicates the variability of rainfall observed during the OND season is influenced by variability of Atlantic Ocean SSTs anomaly. Both SVD modes captured the positive phase of the South Atlantic Ocean Dipole (SAOD) which is characterized by warm sea surface temperature (SST) anomalies in the southwest pole (SWP) and cool SST anomalies in the northeast pole (NEP). The Walker circulation cell observed is due to inhomogeneous warming over the tropical Atlantic Ocean with ascending limb where it is relatively warm in the SWP and descending limb where it is relatively cool in the NEP. Nonsignificant low correlation is observed between the Atlantic Walker circulation index and the Oceanic Indices (dipole mode index [DMI] and Niño3.4). This indicates that the Atlantic Walker circulation cell is an independent system resulting from local ocean–atmosphere interaction and does not depend on the influence of the tropical Indian or Pacific Oceans. Above average rainfall in Tanzania during the OND season is associated with the ascending limb of the Atlantic Walker circulation cell which is enhanced by convection in the western Atlantic Ocean and the latent heat released through the condensation in the mid‐level which is advected by westerly winds aloft towards the study region, enhancing warming, and ultimately enhancing rainfall over Tanzania. [ABSTRACT FROM AUTHOR]

This work aims at detecting to what extent the El Niño Southern Oscillation (ENSO) modulation influences the upper warm temperature anomaly (UWTA) formation in Tanzania during March to May (MAM) season of 1980–2010. The UWTA has known to influence heavy rainfall events through enhanced vertical uplift and deepening surface low pressure. The study is thus critical towards improved early warning system through a better understanding of the mechanisms in the climate system responsible for the above average rainfall. The empirical orthogonal function analysis in this study, revealed the dominant interannual variability mode of the UWTA to be concentrated over the study region. The interannual variability of ENSO and the UWTA shows a moderate relationship during MAM (r =.5328) while a robust association (r =.7905) exists during the previous September to November (SON). Thus, the anomalous sea surface temperature anomaly (SSTA) of the central tropical Pacific (e.g., over Nino 3.4) leads 6 months before the UWTA of the study region and anomalous SSTA over the tropical Indian Ocean (TIO) peak up. Comparatively, the warm phase of ENSO during SON and December to February (DJF) is in phase relationship with the strengthened ascending branch of the Walker circulation over the warm TIO. Further analysis demonstrates that in SON the rising limb of the Walker circulation is the dominant source of uplift and convection enhancement over the warm TIO and later transports warm and moist air (i.e., diabatic heating) aloft for the UWTA formation during SON and DJF. Meanwhile, the Hadley circulation (HC) induced by the SSTA associated with ENSO exhibits the symmetric mode during SON and asymmetric mode in MAM. The asymmetric mode of the HC plays its role in transporting the warm and moist air from the warm TIO towards the study area for the UWTA formation during MAM. [ABSTRACT FROM AUTHOR]

This study analyses the spatial and temporal distribution of heavy rainfall events (HREs) and its associated circulation anomalies over Tanzania during March to May (MAM) rainfall season of 1980–2010. A total of 822 HREs were revealed, concentrated over the northern sector (NS) of the country. Years with anomalous HREs are associated with low-level westerly convergence, advection of moisture from both the Indian Ocean and Congo basin, an upper warm temperature anomaly (UWTA), intensified and well-positioned Intertropical Convergence Zone (ITCZ), and pronounced rising motion since the ascending limb of the Walker type of circulation is centered over Tanzania. The analysis of the UWTA in this study has brought a key factor in exploring the possible likely cause and improved early warning system for the HREs during the MAM rainfall season in Tanzania. Making use of the thermal wind equation and the velocity divergent form of the continuity equation (DFCE), we found that the UWTA results into an upper-level horizontal wind divergence which significantly accelerates vertical ascent, deepening the surface low pressure for an enhanced convective process and HREs formation. [ABSTRACT FROM AUTHOR]

Based on monthly rainfall station data from the National Climate Prediction Center of China Meteorological Administration, reanalysis monthly data from NCEP/NCAR including the monthly mean and long-term mean values for geopotential height, winds of multi-levels, NOAA(National Oceanic and Atmospheric Administration) monthly Sea Surface Temperature (ERSSTV5), the causes of anomalous excessive precipitation in 2021/2022 winter over South China (SC) are investigated by Liang-Kleeman information flow, composite and wave flux methods. The results show that the winter precipitation over SC in 2021/2022 DJF is far more than normal, and the associated circulation patterns are obviously different from those induced by traditional La Niña, especially in the Atlantic and East Asia areas south to Lake Baikal. In 2021/2022 DJF, the Tibet Plateau (TP) exists anomalous cyclone with strong ascending motion, which directly affects the circulation patterns in Eastern China and thus the precipitation in SC. It is a significant causal relationship for the earlier season velocity potential at 850 hPa (related to the anomalous SST) over the tropical Atlantic to later DJF anomalous vertical motions over TP. Especially when the anomalies in tropical Atlantic leads one month before, the relationship is closest. The anomalies of the tropical Atlantic can stimulate the Rossby wave train which propagates downstream, corresponding to the abnormal cyclonic circulation over TP. In the early autumn to winter of 2021/2022, the 850 hPa potential velocity anomalies in the tropical Atlantic were significant with positive phase. The Rossby wave train excited by the potential velocity anomalies and then propagated along the great circle path and global jet stream (GJT) over South Asia (SA), formed an anomalous cyclonic with ascending motion over TP and lead more precipitation over SC in winter of 2021/2022. Winter rainfall, usually accompanying with lower temperature, will bring severely bad influence on traffic, power supply, communication, agriculture and people's lives. The results of this paper can provide a reference for further understanding the causes and mechanism of DJF rainfall over SC. • The winter precipitation over SC in 2021/2022 DJF is extremely more than normal, and the associated circulation patterns are obviously different from those induced by La Niña, especially in the Atlantic and East Asia areas south to Lake Baikal. • Strong ascending motion over TP(Tibet Plateau) affects the circulation patterns directly in eastern China and lead to the excessive precipitation in SC during 2021/2022 DJF. • The anomalies over the tropical Atlantic can stimulate the Rossby wave train and propagate downstream, and the Rossby wave trains allow energy to propagate to TP area with wave flux convergent, contributing certainly to the anomaly cyclone circulation there. [ABSTRACT FROM AUTHOR]

This study diagnoses the cause of the upper-level warm temperature anomaly (UWTA) associated with March–May (MAM) heavy rainfall of 1980–2010 in Tanzania in terms of the empirical orthogonal function (EOF), singular value decomposition (SVD) and dynamical diagnosis. EOF reveals the dominance of enhanced UWTA over the entire study region with strong warming to the northern coast, central, south-western highlands (SWH) and western part of the country. SVD depicts a monopole positive co-variability between the UWTA of the entire study area and SSTA over the entire domain of the Indian Ocean with strong positive coefficients to the central equatorial and western Indian Ocean (WIO). The lead-lag correlation coefficients between the three months running mean for the normalized WIO SSTA and UWTA indices show that, the UWTA formation starts early before MAM with the highest peak in February–April (FMA). The ascending branch of the Walker circulation is the dominant primer for the vertical uplift of warm moist air from the WIO during MAM while convective coupled Kelvin waves (CCKWs) dominate in FMA season. In both seasons, strong positive zonal temperature advection anomalies over the WIO spread towards the study area thereby dominating diabatic cooling and further increase the upper-level tropospheric temperature. Thus, diabatic heating due to enhanced uplift of warm and moist air from enhanced warm SSTA of the WIO warms the upper-level troposphere (i.e., also the UWTA) of the study area through the zonal temperature advection. • The Upper-level Warm Temperature Anomaly (UWTA) formation peaks in February to April (FMA) • Enhanced warm Sea Surface Temperature is the key for the UWTA formation • Convective Coupled Kelvin Waves enhances convection for the UWTA formation in FMA • Walker Circulation enhances convection for the UWTA formation in March to May (MAM) [ABSTRACT FROM AUTHOR]

The intraseasonal reversal of the temperature over East Asia and the sudden stratospheric warming (SSW) are two abrupt events during the winter of 2020/21. The characteristics of these two events and their relationship are the focused issues in this paper. In winter 2020/21, there was a transition from cold to warm over East Asia. The surface air temperature (SAT) in East Asia suddenly changed from cold to warm with long duration. The cold period lasted from 21 November 2020 to 11 January 2021, while the warm period lasted from 19 January to 28 February 2021. And the transition of the cold to the warm was from 12 to 18 January 2021.There were significant differences of the atmospheric circulations between the cold and warm periods in the upper and lower troposphere. During the cold period, both of Ural Mountain High(UH) and Siberian High(SH) were stronger than normal, the Westerly Jet (WJ) was weakened and located to the area farther southerly than usual, the northerly wind anomalies and the cold advection occurred in East Asian; vice versa during the warm period. The mutations of the atmospheric circulations in the upper and lower levels were obvious during the transition period, especially for UH and SH. A strong SSW event occurred in the stratosphere at the beginning of 2021. As a result, the stratospheric polar vortex was largely weakened and deviated to the areas over Ural Mountains and nearby, the polar westerly wind turned to easterly wind and the temperature gradient reversed. The abnormal changes of the temperature and the geopotential height over the Ural Mountains area in the stratosphere were closely related to the SSW. These abnormal signals caused by the SSW gradually transmitted from stratosphere to troposphere over the Ural Mountains and the polar region, leading to the weakening and collapse of tropospheric UH and further caused the transition from cold to warm in East Asia. The SSW may be the most critical factor leading to the turning from cold to warm over East Asia during the winter of 2020/21. • Focuses on two newest and unexpected events during the winter 2020/21. • The intraseasonal reversal of the temperature over East Asia and the sudden stratospheric warming (SSW). • The characteristics of these two events and their relationship are examined.Apart from SSW. • Other factors of affecting the intraseasonal turning are also pointed out and discussed in this paper. [ABSTRACT FROM AUTHOR]

The article presents a study on how eastward shift and extension of Eastward shift and extension of El Niño–Southern Oscillation (ENSO)-induced tropical precipitation anomalies under global warming. Topics discussed include increased precipitation occurs over the equatorial central eastern Pacific; convective heating that modulates global climate by exciting atmospheric teleconnections; and meridional span of the underlying El Niño–related sea surface temperature (SST) anomalies.