Recent Progress in Studies of the Variabilities and Mechanisms of the East Asian Monsoon in a Changing Climate

Located in a monsoon domain,East Asia suffers devastating natural hazards induced by anomalous monsoon behaviors.East Asian monsoon(EAM)research has traditionally been a high priority for the Chinese climate community and is particularly challenging in a changing climate where the global mean temperature has been rising.Recent advances in studies of the variabilities and mechanisms of the EAM are reviewed in this paper,focusing on the interannual to interdecadal time scales.Some new results have been achieved in understanding the behaviors of the EAM,such as the evolution of the East Asian summer monsoon(EASM),including both its onset and withdrawal over the South China Sea,the changes in the northern boundary activity of the EASM,or the transitional climate zone in East Asia,and the cycle of the EASM and the East Asian winter monsoon and their linkages.In addition,understanding of the mechanism of the EAM variability has improved in several aspects,including the impacts of different types of ENSO on the EAM,the impacts from the Indian Ocean and Atlantic Ocean,and the roles of mid-to high-latitude processes.Finally,some scientific issues regarding our understanding of the EAM are proposed for future investigation.

Numerical Simulation on Climate Effects of Freezing-Thawing Processes Using CCM3

A parameterization of soil freezing-thawing physics for use in the land-surface model of the National Center for Atmospheric Research(NCAR) Community Climate Model(CCM3) is developed and evaluated.The new parameterization scheme has improved the representation of physical processes in the existing land surface model.Numerical simulations using CCM3 with improved land-surface processes and with the original land-surface processes are compared against the NCEP reanalysis.It is found that the CCM3 version using the improved land surface model shows significant improvements in simulating precipitation in China during the summer season,the general circulation over East Asia,and wind fields over the Tibet Plateau.For the summer season,the improved model was able to better simulate the Indian summer monsoon components,including the mean northerly wind in the upper troposphere and mean southerly wind in the lower troposphere.

Characteristics of GLDAS soil-moisture data on the Tibet Plateau

In this paper, the applicability of soil-moisture(SM) datasets of GLDAS(Global Land Data Assimilation System) in an alpine region(Tibet Plateau, TP) is investigated. The relations and discrepancies between the GLDAS-NOAH SM(0~10cm) and the observations are compared; the possible reasons for errors over the TP are explored. The results show that GLDAS SM biases mainly show up in errors of values in the nonfrozen period(April to October) and changes of SM along with the temperature, especially during the freezing-thawing process in the frozen period(November to March). The biases of GLDAS SM in the nonfrozen period are mainly caused by the GLDAS precipitation-forcing data. The errors of GLDAS SM in the frozen period are speculated to be induced by the freeze-thaw parameterization scheme in the land-surface model.

Spatial distributions and interannual variations of snow cover over China in the last 40 years

By using the observational snow data of more than 700 weather stations,the interannual temporal and spatial characteristics of seasonal snow cover in China were analyzed.The results show that northern Xinjiang,northeastern China–Inner Mongolia,and the southwestern and southern portions of Tibetan Plateau are three regions in China with high seasonal snow cover and also an interannual anomaly of snow cover.According to the trend of both the snow depth and snow cover days,there are three changing patterns for the seasonal snow cover:The first type is that both snow depth and snow cover days simultaneously increase or decrease;this includes northern Xinjiang,middle and eastern Inner Mongolia,and so on.The second is that snow depth increases but snow cover days decrease;this type mainly locates in the eastern parts of the northeastern plain of China and the upper reaches of the Yangtze River.The last type is that snow depth decreases but snow cover days increase at the same time such as that in middle parts of Tibetan Plateau.Snow cover in China appears to have been having a slow increasing trend during the last 40 years.On the decadal scale,snow depth and snow cover days slightly increased in the 1960s and then decreased in the 1970s;they again turn to increasing in the 1980s and persist into 1990s.

Wavelet analysis of quasi-3-year temperature oscillations in China in last 50 years, and predicted changes in the next 20 years

The wavelet analysis method is used to analyze the annual and winter temperature data of 98 observation stations in China in eight climate zones during the last 50 years （1961-2009）. The periodicities of temperature changes are investigated, and the possible temperature change trends in China in the next 20 years （2012-2029） are also predicted. Our results show that in the inter-annual temperature variability there are pervasive quasi-3- to quasi-4-year cycles, and these cycle changes are relatively steady. The periodic characteristics of the annual temperature changes are clearly different between northern and southern China, and our period superimposition extrapolation shows that both annual and winter temperatures in China will continue to increase in the next 20 years, more so in northern China and in the Qinghai-Xizang Plateau （QXP） than in the southern region, except in the southwest. If temperatures follow historic increasing linear trends, the overall temper- ature is expected to increase by 1℃ between 2010 and 2029.

Abrupt Change in Sahara Precipitation and the Associated Circulation Patterns

This study investigates the changes in inter-annual summer precipitation and the relationship with the atmospheric general circulation in the Sahara Desert occurred in the last 40 years (1971-2010). The results show that the summer precipitation undergone in drought recovery with a strong abrupt change at the end of 20th century. This change in Sahara precipitation is subsequently accompanied with the changes in the atmospheric circulation. The Sahara drought recovery is associated with a significant warming in the tropical and extratropical sea surface temperature, which led to the increase in moisture budget of the tropical African monsoon. The remarkable features such as the strengthening in Arctic high and mid-latitude upper level westerly wind, weakening in subpolar low and upper tropospheric zonal wind over North Africa have shown a distinct relationship with the Sahara precipitation changes.

Features of the Three Dimensional Structures in the Pacific Sub-surface Layer in Summer

The anomaly of the summer sea temperature is analyzed by a spatial-temporal synthetically rotated Empirical Orthogonal Function(REOF)at three different depths(0 m,40 m,and 120 m)over the area 110°E^100°W and 30°S^60°N.The spatial-temporal distribution shows that the“signal”of annual anomaly is stronger in the sub-surface layer than the surface layer,and it is stronger in the eastern equatorial Pacific than in the western area.The spatial structure of the sea temperature anomaly at different layers is related to both the ocean current and the interaction of ocean and atmosphere.The temporal changing trend of the sub-surface sea temperature in different areas shows that the annual mean sea temperature increases and the annual variability evidently increases since the 1980s,and these keep the same trend with the increasing El Nino phenomenon very well.

SARS-CoV-2 Nsp8 induces mitophagy by damaging mitochondria

Autophagy plays an important role in the interaction between viruses and host cells.SARS-CoV-2 infection can disrupt the autophagy process in target cells.However,the precise molecular mechanism is still unknown.In this study,we discovered that the Nsp8 of SARS-CoV-2 could cause an increasing accumulation of autophagosomes by preventing the fusion of autophagosomes and lysosomes.From further investigation,we found that Nsp8 was present on mitochondria and can damage mitochondria to initiate mitophagy.The results of experiments with immunofluorescence revealed that Nsp8 induced incomplete mitophagy.Moreover,both domains of Nsp8 orchestrated their function during Nsp8-induced mitophagy,in which the N-terminal domain colocalized with mitochondria and the C-terminal domain induced auto/mitophagy.This novel finding expands our understanding of the function of Nsp8 in promoting mitochondrial damage and inducing incomplete mitophagy,which helps us to understand the etiology of COVID-19 as well as open up new pathways for creating SARS-CoV-2 treatment methods.

Impacts of Soil Moisture on the Numerical Simulation of a Post-Landfall Storm

Surface heat and moisture fluxes are important to the evolution of a tropical storm after its landfall. Soil moisture is one of the essential components that influence surface heating and moisture fluxes. In this study, the impact of soil moisture on a pre-landfall numerical simulation of Tropical Storm Bill(2015), which had a much longer lifespan over land, is investigated by using the research version of the NCEP Hurricane Weather Research and Forecasting(HWRF) model. It is found that increased soil moisture with SLAB scheme before storm's landfall tends to produce a weaker storm after landfall and has negative impacts on storm track simulation. Further diagnoses with different land surface schemes and sensitivity experiments indicate that the increase in soil moisture inside the storm corresponds to a strengthened vertical mixing within the storm boundary layer, which is conducive to the decay of storm and has negative impacts on storm evolution. In addition, surface diabatic heating effects over the storm environment are also found to be an important positive contribution to the storm evolution over land, but their impacts are not so substantial as boundary layer vertical mixing inside the storm. The overall results highlight the importance and uncertainty of soil moisture in numerical model simulations of landfalling hurricanes and their further evolution over land.

Evaluation of the WRF-Lake Model over Two Major Freshwater Lakes in China

This paper evaluates the performance of the Weather Research and Forecasting(WRF) model coupled with a lake scheme over the Lake Poyang and Lake Dongting regions. We choose several cases with different weather characteristics, including winter with/without precipitation and summer with/without precipitation, and conduct a series of experiments(without the lake model, with the default lake model, and with a calibrated lake model that adjusts the water absorption, extinction coefficients, and surface roughness length) for each case. The results show that the performance of the lake model is significantly affected by the weather conditions. For the winter with precipitation cases, the performance of the default lake model is even worse than without the lake model, but the calibrated lake model can obviously reduce the biases of 2-m temperature and dew-point temperature. Although the performance of the default and new calibrated models is intricate for other cases, the new calibrated model has prominent advantages for 2-m dew-point temperature. Moreover, a long-term simulation of five months also shows that the new calibrated coupled lake model performs better than the default one. These imply that the new calibrated coupled lake model is more suitable to be used in studies of the effects of Lake Poyang and Lake Dongting on regional weather and climate.