Erratum to: An Isentropic Mass Circulation View on the ExtremeCold Events in the 2020/21Winter

Erratum to:Yu,Y.Y.,Y.F.Li,R.C.Ren,M.Cai,Z.Y.Guan,and W.Huang,2021:An isentropic mass circulation view on the extreme cold events in 2020/21 Winter.Adv.Atmos.Sci.,38(6),957−965,https://doi.org/10.1007/s00376-021-1289-2.

An Isentropic Mass Circulation View on the Extreme Cold Events in the 2020/21 Winter

Three extreme cold events successively occurred across East Asia and North America in the 2020/21 winter.This study investigates the underlying mechanisms of these record-breaking persistent cold events from the isentropic mass circulation(IMC)perspective.Results show that the midlatitude cold surface temperature anomalies always co-occurred with the high-latitude warm anomalies,and this was closely related to the strengthening of the low-level equatorward cold air branch of the IMC,particularly along the climatological cold air routes over East Asia and North America.Specifically,the two cold surges over East Asia in early winter were results of intensification of cold air transport there,influenced by the Arctic sea ice loss in autumn.The weakened cold air transport over North America associated with warmer northeastern Pacific sea surface temperatures(SSTs)explained the concurrent anomalous warmth there.This enhanced a wavenumber-1 pattern and upward wave propagation,inducing a simultaneous and long-lasting stronger poleward warm air branch(WB)of the IMC in the stratosphere and hence a displacement-type Stratospheric Sudden Warming(SSW)event on 4 January.The WB-induced increase in the air mass transported into the polar stratosphere was followed by intensification of the equatorward cold branch,hence promoting the occurrence of two extreme cold events respectively over East Asia in the beginning of January and over North America in February.Results do not yield a robust direct linkage from La Niña to the SSW event,IMC changes,and cold events,though the extratropical warm SSTs are found to contribute to the February cold surge in North America.

On the Interrelation between Spring Bihemispheric Circulations at Middle and High Latitudes

Bihemispheric atmospheric interaction and teleconnection allow us to deepen our understanding of large-scale climate and weather variability. This study uses 1979-2017 spring NCEP reanalysis to show that there is interrelation between bihemispheric circulations at the extratropics. This is regarded as a significant negative correlation between the Antarctic and the Arctic regional surface air pressure anomalies, which is induced by interhemispheric oscillation (IHO) of the atmospheric mass. The spatial pattern of IHO is characterized by antiphase extratropical airmass anomalies and geopotential height anomalies from the troposphere to stratosphere between the Southern and Northern Hemisphere. IHO is closely related to stronger bihemispheric low-frequency signals such as Antarctic Oscillation and Arctic Oscillation, thereby demonstrating that IHO can be interpreted as a tie in linking these two dominant extratropical circulations of both hemispheres. IHO is associated with a strong meridional teleconnection in zonal winds from the middle-high troposphere to the lower stratosphere, with the wind anomalies in the form of alternate positive-negative wavy bands extending from the Antarctic to Arctic region, which act as a possible approach to interactions between the bihemispheric atmospheric mass. It is argued that IHO-related omega angular momentum anomalies led by the extratropical atmosphere cause the meridional teleconnection of relative angular momenta, thereby giving rise to the zonal wind anomalies. The modeling of GFDL and UKMO as components of the CMIP5 project have been verified, achieving the related IHO structure shown in the present paper.

Analysis on mechanisms of anomalous variations of tropopause pressure over the Tibetan Plateau during summer in Northern Hemisphere

Using the monthly mean data from NCEP-NCAR reanalysis, through building tropopause pressure index, we investigated the mechanisms of anomalous variations of tropopause pressure over the Tibetan Plateau during summer in Northem Hemisphere. For comparative analysis we selected representative years of 1992 and 1998 to study, and they were respectively the highest and the lowest year oftropopause pressure anomaly over the Tibetan Plateau. The results are summarized as follows： （1） Over the Tibetan Plateau, the variations of tropopause pressure are well correlated respectively with anomalous temperature and geopotential height in both troposphere and stratosphere. Besides, the anomalous tropopause pressure has also close relation with anomalous surface temperature in the Tibetan Plateau. In 1992, the surface temperature was anomalously low, correspondingly, the tropopause pressure over the Tibetan Plateau was anomalously high; but in 1998, the opposite was the case. （2） Over the Tibetan Plateau, the correlation of tropopause pressure and OLR （Outgoing Longwave Radiation） is found to be positive. Furthermore, by further diagnosing the circulation fields between 850 hPa and 200 hPa levels and the whole troposphere vapour field, we found out that the anomalously high tropopause pressure in 1992 corresponded to the anticyclonic divergence of low level wind fields and the cyclonic convergence of high level wind fields, and coupled with divergence of the whole troposphere vapour fields along with the South Asian High weakened at the same time. While in 1998, the case was opposite to that in 1992. These facts indicated that the anomalous convection resulted in the significant difference oftropopause pressure in 1992 and 1998 over the Tibetan Plateau. （3） The vertically integrated heat budget anomalies were responsible for explaining tropopause pressure anomalies in 1992 and 1998 over the Tibetan Plateau.

An unusual high ozone event over the North and Northeast China during the record-breaking summer in 2018

Under the background of global warming,the summer temperature of the North and Northeast China(NNEC)has significantly increased since 2017,which was accompanied by the aggravated ozone(O_(3))pollution.In 2018,the NNEC experienced a record-breaking summer of the past 40 years.Influenced by the abnormal high temperatures,a regional ozone event occurred on 2-3 August,over 63%of 79 selected cities in the NNEC were exposed to O_(3)pollution,and the maximum value of MDA8 O_(3)reached 268μg/m 3.Observations indicated that ozone concentrations agree well with the maximum temperature at 2 meters(MT2M)over NNEC with a correlation coefficient of 0.69.During the pollution episode,strong downdraft in the local high(35°N-42.5°N,112.5°E-132.5°E;LH)over the NNEC created the favourable meteorological conditions for O_(3)formation.By analyzing the horizontal wind and wave activity fluxes(WAFs)at 200 h Pa,we found that the LH formation was resulted from the Rossby wave propagation from upstream along the mid-latitude Asian jet.The split polar vortex intrusion further strengthened the amplitude of the Rossby wave and reinforced the LH.Moreover,a secondary circulation between Typhoon Jongdari and the LH contributed to the enhanced LH with strong subsidence.On the other hand,the stratospheric intrusions under the deep subsidence also contributed to the enhanced surface O_(3).In this study,the deep-seated meteorological dynamical mechanisms contributing to the abnormal high temperatures were investigated,which can lead to a better understanding of the regional O_(3)pollution over NNEC under the global-warming background.

Joint Impacts of SSTA in Tropical Pacific and Indian Oceans on Variations of the WPSH

Using the NCEP/NCAR reanalysis and HadlSST sea surface temperature （SST） data, the joint effects of the tropi-cal Indian Ocean and Pacific on variations of area of the summertime western Pacific subtropical high （WPSH） for period 1980-2016 are investigated. It is demonstrated that the central tropical Indian Ocean （CTI） and central equat-orial Pacific （CEP） are two key oceanic regions that affect the summertime WPSH. During autumn and winter, warm SST anomalies （SSTAs） in CEP force the Walker circulation to change anomalously, resulting in divergence anom- alies over the western Pacific and Maritime Continent （MC）. Due to the Gill-type response, the abnormal anticyclo- nic circulation is generated over the western Pacific and South China Sea （SCS）. In the subsequent spring, the warm SSTAs in CEP weaken, while the SST over CTI demonstrates a lagged response to Pacific SSTA. The warm CTI-SSTA and CEP-SSTA cooperate with the eastward propagation of cold Kelvin waves in the western Pacific, leading to the eastward shift of the abnormal divergence center that originally locates at the western Pacific and MC. The an-ticyclone forced by this divergence subsequently moves eastward, leading to the intensification of the negative vorti- city there. Meanwhile, warm SSTA in CTI triggers eastward propagating Kelvin waves, which lead to easterly anom- alies over the equatorial Indian Ocean and Indonesia, being favorable for maintenance and intensification of the anti-cyclone over the SCS and western Pacific. The monsoonal meridional-vertical circulation strengthens, which is fa-vorable for the intensification of the WPSH. Using SSTA over the two key oceanic regions as predictors, a multiple regression model is successfully constructed for prediction of WPSH area. These results are useful for our better un-derstanding the variation mechanisms of WPSH and better predicting summer climate in East Asia.

Interannual Variability of Summertime Outgoing Longwave Radiation over the Maritime Continent in Relation to East Asian Summer Monsoon Anomalies

The Maritime Continent（MC） is under influences of both the tropical Pacific and the Indian Ocean. Anomalous convective activities over the MC have significant impacts on the East Asian summer monsoon（EASM） and climate in China. In the present study, the variation in convective activity over the MC in boreal summer and its relationship to EASM anomalies are investigated based on regression analysis of NCEP–NCAR reanalysis and CMAP [Climate Prediction Center（CPC） Merged Analysis of Precipitation] data, with a focus on the impacts of ENSO and the Indian Ocean Dipole（IOD）. The most significant interannual variability of convective activity is found over 10°S–10°N, 95°–145°E, which can be roughly defined as the key area of the MC（hereafter, KMC）. Outgoing longwave radiation anomaly（OLRA） exhibits 3- to 7-yr periodicities over the KMC, and around 70% of the OLRA variance can be explained by the ENSO signal. However, distinct convection and precipitation anomalies still exist over this region after the ENSO and IOD signals are removed. Abnormally low precipitation always corresponds to positive OLRA over the KMC when negative diabatic heating anomalies and anomalous cooling of the atmospheric column lead to abnormal descending motion over this region. Correspondingly, abnormal divergence occurs in the lower troposphere while convergence occurs in the upper troposphere, triggering an East Asia–Pacific/Pacific–Japan（EAP/PJ）-like anomalous wave train that propagates northeastward and leads to a significant positive precipitation anomaly from the Yangtze River valley in China to the islands of Japan. This EAP/PJ-like wave pattern becomes even clearer after the removal of the ENSO signal and the combined effects of ENSO and IOD, suggesting that convective anomalies over the KMC have an important impact on EASM anomalies. The above results provide important clues for the prediction of EASM anomalies and associated summer precipitation anomalies in China.

A New Year Message from Chinese Science Bulletin

中国科学告示的编辑 A

Interdecadal Change in the Eurasia–Pacific Anti-Phase Relation of Atmospheric Mass and Its Possible Link with PDO

Based on the known climatic shift that occurred in 1976, we divide the present study period into two epochs： epoch-I, for 1958 1976; and epoch-II, for 1977-2002. Using ERA-40 and the 20th century reanalysis data, we in- vestigate the interdecadal change in the Eurasia-Pacific anti-phase relation （EPAR） pattern of atmospheric mass （AM） during boreal winter before and after 1976. It is found that anomalous AM over lands is highly and negatively correlated with anomalous AM over oceans in the Northern Hemisphere during the winter season. This correlation does not change much from epoch-I to epoch-II. However, the correlation pattern of surface air pressure anomalies with variations of anomalous AM over lands changes remarkably from epoch-I to epoch-lI; the EPAR pattern emerges evidently in the later period, whereas it is not significant in epoch-I. The occurrence of the EPAR pattern in epoch-II may be attributable to the Pacific Decadal Oscillation （PDO）. The PDO may modulate the EPAR pattern in two ways. Firstly, the interdecadal component of the PDO as a background may modulate the intensities of the Aleut- ian low, East Asian trough, and westerly flow, acting as a waveguide during the warm phase （epoch-Ⅱ） of the PDO. Secondly, the interannual variations of sea surface temperature anomalies in the North Pacific, in association with the PDO, may affect the interannual variations of AM, which facilitates the existence of the EPAR pattern in epoch-Ⅱ only. With the teleconnection pattern having changed before and after 1976, winter climate anomalies, including rain- fall and temperature, are found to be different in many regions in the Northern Hemisphere between epoch-I and epoch-Ⅱ. All the results of the present work are meaningful for a better understanding of climate anomalies during boreal winter.

Seasonal Variations of Aerosol Optical Depth over East China and India in Relationship to the Asian Monsoon Circulation

Seasonal variation features of aerosol optical depth （AOD） over East China and India in association with the Asian monsoon system are investigated, based on the latest AOD data derived from the Moderate Resolution Imaging Spec-troradiometer （MODIS） aboard the Terra satellite, the NCEP Final （FNL） Operational Global Analysis data, the Cli-mate Prediction Center （CPC） Merged Analysis of Precipitation （CMAP） data, and the NCEP/NCAR reanalysis data from March 2000 to February 2017. The results indicate that AOD in East China is significantly larger than that in India, especially in spring. The seasonal mean AOD in East China is high in both spring and summer but low in fall and winter. However, the AOD averaged over India is highest in summer and lower in spring, fall, and winter. Ana-lysis reveals that AOD is more closely related to changes in surface wind speed in East China, while no obvious rela-tion is found between precipitation and the AOD distribution on the seasonal timescale. As aerosols are mainly dis-tributed in the atmospheric boundary layer （ABL）, the stability of the ABL represented by Richardson number （Ri） is closely correlated with spatial distribution of AOD. The upper and lower tropospheric circulation patterns signific-antly differ between East China and India, resulting in different effects on the AOD. The effect of advection associ-ated with lower tropospheric circulation on the AOD and the influence of convergence and divergence on the AOD distribution play different roles in maintaining the AOD in East China and India. These results improve our under-standing of the mechanism responsible for and differences among the aerosol changes in East China and India.