Search

This article evaluated the performance of 19 Coupled Model Intercomparison Project phase 6 (CMIP6) models in simulating the Arctic sea ice from the perspective of annual cycle, spatial pattern and temporal variation. Based on the evaluation, five models with better comprehensive performance capacity were optimized as the ensemble to project the response of the East Asian winter climate to the sea ice‐free Arctic occurring under the SSP2‐4.5 and SSP5‐8.5 scenarios, respectively. The ensemble projections indicate that the sea ice‐free Arctic is followed by a weakening of the East Asian winter monsoon, which is characterized with the shallower East Asian trough and weaker East Asian jet stream. Concurrently, the winter surface net radiation flux is projected to increase in the East Asian‐western North Pacific region. These changes favour large‐scale warming in the East Asian‐western North Pacific region. Moreover, the warming is more pronounced under the sea ice‐free Arctic of SSP2‐4.5 than under that of SSP5‐8.5. The winter precipitation tends to increase along the East Asian coast from South China to the Sea of Okhotsk. Such an increase is closely associated with the enhancement of low‐level moisture. Due to larger enhancement of moisture, there appears greater increase of precipitation in the monsoon region from South China to Japan under the sea ice‐free Arctic of SSP5‐8.5 compare to that under SSP2‐4.5. Substantial changes are also projected for the temperature and precipitation extremes, such as a general increase in warm days and warm nights and an overall intensification of extreme precipitation in the East Asian‐western North Pacific region. [ABSTRACT FROM AUTHOR]

This study investigates the relationship between the Antarctic sea ice concentration (SIC) and the precipitation variability in Tanzania during March to May (MAM) season from 1978 to 2017. It is found that the MAM SIC over the Weddell (Ross) sea is negatively correlated with the MAM precipitation, particularly over northern (southern) Tanzania, signifying that the high (low) MAM SIC over the Weddell (Ross) sea is associated with suppressed (enhanced) rainfall in Tanzania. The atmospheric circulations related to the MAM SIC anomalies were further analysed. It is revealed that the positive MAM SIC anomalies in the Weddell sea and the Ross sea are associated with the upper‐level wave train patterns propagating from the high latitudes to the low latitudes of the Southern Hemisphere, which results in anomalous upper‐level cyclonic circulation over the western Indian Ocean and Tanzania. The upper‐level cyclonic circulation anomaly favours the low‐level divergence and results in the subsidence over Tanzania. Moreover, the low‐level wind outflow over Tanzania due to divergence reduces the water vapour supply to Tanzania. This background is unfavourable for the occurrence of precipitation and thus decreases the precipitation in Tanzania. The situation is reversed for the negative MAM SIC anomalies over the Weddell sea and the Ross sea, conducive to the increase of precipitation over Tanzania. [ABSTRACT FROM AUTHOR]

This study evaluates the performance of 43 Coupled Model Intercomparison Project phase 6 (CMIP6) models in reproducing annual cycle, climatology, and trend of observed precipitation over East Africa during 1950–2014. The results show that the CMIP6 models display good performance in simulating the annual cycle (i.e., bimodal pattern) of East African precipitation; however, most models and the multimodel ensemble mean (ENSEM) underestimate the March to May (MAM) precipitation while overestimating the October to December (OND) precipitation. Spatially, most models seem to perform relatively better in simulating OND precipitation compared to MAM season, despite wet (dry) biases over most parts of East Africa with the wettest (driest) biases over the Lake Victoria basin (southeastern Tanzania) during OND (MAM). The metrics have shown that nine models (i.e., MPI‐ESM1‐2‐HR, AWI‐CM‐1‐MR, MPI‐ESM1‐2‐LR, IPSL‐CM6A‐LR, CAS‐ESM2‐0, BCC‐CSM2‐MR, NorESM2‐LM, CESM2‐WACCM, and CMCC‐CM2‐SR5) outperform the other individual models during both OND and MAM. Compared with individual models, the ENSEM better agrees with the observation. Besides, the ENSEM and most models can reproduce the increasing trend in OND precipitation as observed over East Africa. However, for the secular change of MAM precipitation, given that half of the models show increasing trends, the ENSEM simulation produces an inconsistent trend with the observation. The ensemble of the above nine models with better performance projects an increase of precipitation averaged over East Africa in both MAM and OND by the end of the 21st century, with larger changes under SSP5‐8.5 than under SSP2‐4.5. Spatially, the largest percentage increase in MAM precipitation is projected to occur in central Tanzania and northwestern Kenya, while southeastern Tanzania shows the greatest percentage decrease. The projected percentage increases in OND precipitation are larger in the northeastern highlands of Tanzania and northwest Kenya. [ABSTRACT FROM AUTHOR]

China has experienced dramatic warming in summer mean temperature since the early 1990s, leading to precipitation variation across the region. We have studied the variation of rainy‐season (April–September) precipitation in eastern China during 1961–2016. Overall, we found that rainy‐season precipitation increased in the south and decreased in the north during 1992–2016 (PII) compared to 1961–1991 (PI). By defining rainfall‐belt indices of intensity and central location, we found that the southern rainfall‐belt during the main rainy‐season tends to produce much more‐intense precipitation during PI relative to PII, in contrast to the northern rainfall‐belt, which tends to have less‐intense precipitation during PII. Despite some fluctuations, the central positions of neither the northern nor the southern rainfall‐belts exhibit a statistically significant difference between the two periods. Unlike during PI, during PII, there is an obvious anticyclone over the Lake Baikal region. This anticyclone has caused anomalous north winds flowing from north‐central to southwestern China, leading to weakening of the northward moisture transport. Also, regions such as northeastern, north‐central, and southwestern China have been controlled by negative geopotential height anomalies and weak vertical air‐motion anomalies, resulting in drying from north to southwestern China. At the same time, the enhanced water‐vapour convergence in the southeastern coastal region of China favours increased precipitation there. These processes working in concert created the drying‐north–wetting‐south pattern in the main rainy‐season during 1961–2016. The change in rainfall‐belt intensity in eastern China has also shown a close relationship with the change in vapour transport from low latitudes. The weakened land‐sea thermal difference in the East Asia–Northwest Pacific region, which has weakened water‐vapour and atmospheric circulation, has also played a role in the change of rainfall‐belt intensity. [ABSTRACT FROM AUTHOR]

A severe low‐temperature snowstorm and ice freezing event occurred in China in early 2018. This event was similar to that occurred in early 2008 but with a weaker intensity and salient difference in location and extent. The reason for this discrepancy was investigated in this study using station data and atmospheric reanalysis data. The results reveal that two different circulation patterns (i.e., zonal dipole pattern and meridional dipole pattern) over the mid‐high latitudes of Eurasia played an important role. The zonal dipole pattern, which is closely related to the 2018 event, is characterized by positive anomalies over the Ural Mountains and negative anomalies over Lake Baikal in the 500 hPa geopotential height field. This pattern can cause intense low temperatures in northern China through its influence on the anomalous cyclone over Northeast Asia. The meridional dipole pattern, which is highly associated with the 2008 event, is characterized by positive anomalies over Siberia and negative anomalies over Asia in the 500 hPa geopotential height field. This pattern corresponds to a strong East Asian winter monsoon (EAWM) and can drive cold air to move further southward, causing nearly nationwide chilly weather, particularly in northwestern China and south of the Yangtze River valley. The two patterns, combined with the strengthened western Pacific subtropical high (WPSH), have a synergistic role in the occurrence of snowfall. However, these patterns have weak correlations with the number of icy days but provide favourable conditions for ice freezing events. [ABSTRACT FROM AUTHOR]

ABSTRACT Based on the high-resolution gridding data ( CN05) from 2416 station observations, a grid dataset of temperature and precipitation extreme indices with the resolution of 0.5° × 0.5° for China region was developed using the approach recommended by the Expert Team on Climate Change Detection and Indices. This article comprehensively presents temporal and spatial changes of these indices for the time period 1961-2010. Results showed widespread significant changes in temperature extremes consistent with warming, for instance, decreases in cold extremes and increases in warm extremes over China. The warming in the coldest day and night is larger than the warmest day and night, respectively, which is concurrent with the coldest night larger than the coldest day and the warmest night larger than the warmest day. Changes in the number of the cold and warm nights are more remarkable than the cold and warm days. Changes in precipitation extremes are, in general, spatially more complex and exhibit a less widespread spatial coverage than the temperature indices, for instance, the patterns of annual total precipitation amount, average daily precipitation rate, and the proportion of heavy precipitation in total annual precipitation are similar with negative trends in a southwest-northeast belt from Southwest China to Northeast China while positive trends in eastern China and northwestern China. The consistency of changes in climate extremes from the CN05 with other datasets based on the stations and reanalyses is also analysed. [ABSTRACT FROM AUTHOR]

Changes of the upper-tropospheric temperature teleconnection and the associated atmospheric circulations in spring (Mar-April-May, MAM) during the mid-Holocene are preliminarily examined by using the CCSM3 simulation data archived in the Paleoclimate Modeling Intercomparison Project (PMIP) database. The simulation result shows that in the mid-Holocene the atmospheric circulation over the Asian-North Pacific region showed the variability of the teleconnection pattern resembling the present Asian-Pacific oscillation (APO), which is characterized by a warming (cooling) upper troposphere over Asia corresponding to a cooling (warming) upper troposphere over the North Pacific and indicates a thermal contrast between Asia and the North Pacific. In comparison with the present climate, the mid-Holocene upper-tropospheric temperature in spring was modelled to be lower over Asia and higher over the North Pacific, indicative of a weaker spring APO. Associated with such a condition, both the upper-tropospheric high (low) and the lower-tropospheric low (high) over Asia (central-eastern Pacific) were weakened in the mid-Holocene. Accordingly, anomalous descending (ascending) motion appeared over East Asia (central-eastern Pacific). This circulation background is unfavourable (favourable) for the occurrence of precipitation, and thus the mid-Holocene precipitation decreases (increases) in this region as compared with the present. Hence, the change of the spring thermal contrast between Asia and the North Pacific played a crucial role in the anomalies of the atmospheric circulations and precipitation over the Asian-Pacific region during the mid-Holocene. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]