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Deep convection in the Tibetan Plateau--southern Asian monsoon region (TP--SAMR) is analyzed using CloudSat and Cloud--Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data for the boreal summer season (June--August) from 2006 to 2009. Three subregions are defined--the TP, the southern slope of the plateau (PSS), and the SAMR--and deep convection properties (such as occurrence frequency, internal vertical structure, system size, and local environment) are compared among these subregions. To cast them in a broader context, four additional regions that bear some similarity to the TP--SAMR are also discussed: East Asia (EA), tropical northwestern Pacific (NWP), and western and eastern North America (WNA and ENA, respectively). The principal findings are as follows: 1) Compared to the other two subregions of the TP--SAMR, deep convection over the TP is shallower, less frequent, and embedded in smaller-size convection systems, but the cloud tops are more densely packed. These characteristics of deep convection over the TP are closely related to the unique local environment, namely, a significantly lower level of neutral buoyancy (LNB) and much drier atmosphere. 2) In a broader context in which all seven regions are brought together, deep convection in the two tropical regions (NWP and SAMR; mostly over ocean) is similar in many regards. A similar conclusion can be drawn among the four subtropical continental regions (TP, EA, WNA, and ENA). However, tropical oceanic and subtropical land regions present some significant contrasts: deep convection in the latter region occurs less frequently, has lower cloud tops but comparable or slightly higher tops of large radar echo (e.g., 0 and 10 dB Z), and is embedded in smaller systems. The cloud tops of the subtropical land regions are generally more densely packed. Hence, the difference between the TP and SAMR is more of a general contrast between subtropical land regions and tropical oceanic regions during the boreal summer. 3) Deep convection over the PSS possesses some uniqueness of its own because of the distinctive terrain (slopes) and moist low-level monsoon flow. 4) Results from a comparison between the daytime (1:30 p.m.) and nighttime (1:30 a.m.) overpasses are largely consistent with researchers'' general understanding of the diurnal variation of tropical and subtropical deep convection. [ABSTRACT FROM AUTHOR]

The structure and evolution features of the quasi-biweekly (10–20 day) oscillation (QBWO) in boreal spring over the tropical Indian Ocean (IO) are investigated using 27-yr daily outgoing longwave radiation (OLR) and the National Centers for Environment Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis data. It is found that a convective disturbance is initiated over the western IO and moves slowly eastward. After passing the central IO, it abruptly jumps into the eastern IO. Meanwhile, the preexisting suppressed convective anomaly in the eastern IO moves poleward in the form of double-cell Rossby gyres. The analysis of vertical circulation shows that a few days prior to the onset of local convection in the eastern equatorial IO an ascending motion appears in the boundary layer. Based on the diagnosis of the zonal momentum equation, a possible boundary layer–triggering mechanism over the eastern equatorial IO is proposed. The cause of the boundary layer convergence and vertical motion is attributed to the free-atmospheric divergence in association with the development of the barotropic wind. It is the downward transport of the background mean easterly momentum by perturbation vertical motion during the suppressed convective phase of the QBWO that leads to the generation of a barotropic easterly—the latter of which further causes the free-atmospheric divergence and, thus, the boundary layer convergence. The result suggests that the local process, rather than the eastward propagation of the disturbance from the western IO, is essential for the phase transition of the QBWO convection over the eastern equatorial IO. [ABSTRACT FROM AUTHOR]

How land cover differences affect runoff and sediment and their relationship with precipitation are largely unknown on the Qinghai–Tibet Plateau. This study was designed to examine precipitation-runoff processes using the runoff observation plots on the 30° slope surfaces. Three plots were selected with vegetative cover average of 30, 68, and 93%. Our results show that runoff with 30% land coverage is larger than those with 68 and 93%, under the same precipitation form and amount in an alpine meadow. The mean sediment per precipitation event is two to four times greater in an area with 30% vegetative cover compared with those in 68 and 93% vegetative cover. Both runoff and mean sediment yields increased with vegetative cover from 30 to 68 and 93%. The precipitation form also affects the runoff and sediment yield. Comparing sleet and rainfall, the runoff yield resulted from melted snow is maximal, but the sediment yield is minimal. Based on the runoff yields of precipitation, the runoff coefficients on a sloping surface of 30° with vegetative cover of 30, 68, and 93% are 5.3, 2.5, and 1.9%, respectively. Quadratic parabolic curves better describe the relationships of runoff and sediment with precipitation on the Qinghai–Tibet Plateau. Our results suggest that vegetation is a major control on runoff and sediment production in the permafrost region. [ABSTRACT FROM AUTHOR]

The article discusses the new integrated observational system over the Tibetan Plateau (NIOST) that was implemented in China since 2005. It says that the study is supported by the Chinese-Japanese joint international cooperation program, and implemented by the Chinese Academy of Meteorological Sciences (CAMS) of the China Meteorological Administration (CMD). The NIOST was realized to provide a mechanism for transferring the research results from field experiments into a forecast capability, as well as to better research activities by providing available and long-term data sets.

Resolution of a complex Hermitian matrix derived from monthly mean 850-hPa wind fields during the summer season (June–August) from 1968 to 2004 revealed four different modes of East Asian summer monsoon (EASM) variability. The leading EASM mode, accounting for 19.6% of the variance, is characterized by two different modes (M11 and M12) or their combination. Both portray a closed cyclonic or anticyclonic circulation anomaly over the western North Pacific (WNP), South China Sea (SCS), and southeastern China; corresponding anomalous geopotential height fields show a wave train structure from the WNP across Japan, the Okhotsk Sea, and Alaska to North America. Thus, the leading EASM mode characterizes the teleconnection pattern of the WNP-EASM. The correlation between M11 (M12) and the dynamic index for the WNP-EASM is 0.85 (0.51). M11 has leading spectral peaks at 15 and 3 yr, whereas M12 displays a predominant peak at 2 yr. It is found that M11 has interdecadal variations, with the transition years being circa 1973 and 1989, respectively. M11 is closely related to air–sea interactions in the SCS and the northwestern Pacific, and its association with the convective heat source over the northwestern Pacific is secondary. In contrast, M12 is closely related to the tropical convective heat source rather than tropical western Pacific sea surface temperature (SST). The second EASM mode, accounting for 12.8% of the variance, is identified and characterized by two distinct and alternating modes or their linear combination (M21 and M22). One mode (M21) closely relates to the dual blocking high pattern detected in anomalous sea level pressure (SLP) and 500-hPa geopotential heights over the Ural Mountains and the Okhotsk Sea. The other (M22) corresponds to a dipole blocking anomaly in anomalous SLP and geopotential heights, with opposing anomalous centers in the south of Japan and the Korean peninsula, and the area between Lake Baikal and the Okhotsk Sea. M22 shows significant correlations with summer mean rainfall in southern and southeastern China. Thus, a single index of EASM is inappropriate for investigating and predicting the EASM. [ABSTRACT FROM AUTHOR]

We identified the Asian–Pacific Oscillation (APO) and its associated index, a zonal teleconnection pattern over the extratropical Asian–Pacific region. This was done through the correlation and empirical orthogonal function (EOF) analyses on the summer mean tropospheric eddy temperature from the monthly European Center for Medium-Range Weather Forecast reanalysis. The APO reflects an out-of-phase relationship in variability of the eddy temperature between Asia and the North Pacific and is associated with the out-of-phase relationship in atmospheric heating. The APO index shows a decadal variation, tending to a high-index polarity before 1975 and afterward to a low-index polarity. Moreover, the APO index has a quasi-5-year period. With higher APO-index conditions in the upper troposphere, the summer South Asian high and the North Pacific trough are stronger, while the westerly jet stream over Asia and the easterly jet stream over South Asia strengthen. Also, the Asian low and the North Pacific subtropical high are stronger in the lower troposphere. The anomalous southerlies prevail at the midlatitudes of East Asia, accompanied by a more northward Mei-yu front, and the anomalous westerlies prevail over South Asia. Summer rainfall increases in North China, South China, and South Asia, while it decreases from the valley of the Yangtze River to southern Japan, and near the Philippines. [ABSTRACT FROM AUTHOR]

Using the 5-day averaged data from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis, and precipitation from rain gauge stations in China for the period 1981–2000, we investigated seasonal variations and associated atmospheric circulation and precipitation of the southwesterly wind over eastern China. The southwesterly wind over eastern China begins earliest over southeastern China and strengthens gradually from spring to the early summer, as it extends northward. The strengthening of the spring southwesterly wind, the tropospheric upward motion, and the convergence of low-level water vapor over southeastern China results in the beginning of the local rainy season. The beginning of the Mei-yu (Plum rainfall) is connected with the northward march of the southwesterly wind. The southwesterly wind reaches the valley of the Yangtze River in the early summer and northern China in the middle summer. This signifies an onset of the large-scale southwesterly wind over eastern China. Accordingly, the rain belt over southeastern China moves to the valley of the Yangtze River in the early summer and to northern China in the middle summer. Moreover, the southerly wind extends southward to the South China Sea from the spring to summer, though it does not stretch from the South China Sea to southeastern China at those times. The strengthening of the southerly wind over southeastern China is associated with a weakening/strengthening of the eastward/westward subtropical tropospheric temperature gradient between southwestern China and the western North Pacific. The developments of a low-pressure system over southwestern China and the subtropical high-pressure system over the western North Pacific may contribute to the strengthening of the southwesterly wind. A northward advance of the high-pressure system favors the southwesterly wind stretching from southeastern China to northern China. The onset of the Indian summer monsoon also strengthens the summer southwesterly wind over eastern China. [ABSTRACT FROM AUTHOR]

Determinations of bottom scattering strength in the decade below 1 kHz under downward refracting conditions have been made using acoustic reverberation and transmission data from the 2001 East China Sea Asian Seas International Acoustic Experiment (ASIAEX). The measurements were performed using explosive sources and receiving hydrophones in ship-suspended vertical-line arrays. The focus of this paper has been the dependence of bottom scattering strength on the frequency and characterization of the uncertainties associated with the extraction of scattering strength from reverberation. The derived bottom scattering strength gradually rises with frequency from 100-300 Hz and then more rapidly above 300 Hz. A potential explanation suggests that the frequency variation results from two scattering mechanisms, rough layer scattering at the low end of the band and sediment near-surface volume scattering at the high end. The spatial extrapolation of these results is explored by comparing them with similarly derived scattering strengths using data obtained under the Navy's Harsh Environments Program at a somewhat separated site (56 km) under environmental conditions similar to those during ASIAEX. In the ASIAEX analysis, it has been found that the largest source of uncertainty in the scattering-strength frequency dependence arises from persistence of finite-amplitude effects associated with the source signal. [ABSTRACT FROM AUTHOR]

This is an exploratory study to investigate the spatial and temporal characteristics of east China’s (EC) river runoff and their relationship with precipitation and sea surface temperature (SST) at the continental scale. Monthly mean data from 72 runoff stations and 160 precipitation stations in EC, covering a period between 1951 and 1983, are used for this study. The station river runoff data have been spatially interpolated onto 1° grid boxes as runoff depth based on an extracted drainage network. Comparing runoff depth with precipitation shows that seasonal variation in runoff is consistent with the development of the summer monsoon, including the delayed response of runoff in several subregions. The dominant spatial scales and temporal patterns of summer runoff and precipitation are studied with empirical orthogonal function (EOF) analysis and wavelet analyses. The analyses show interannual, biennial, and longer-term variations in the EOF modes. South–north dipole anomaly patterns for the first two runoff EOF’s spatial distributions have been identified. The first/second runoff principal components (PCs) are highly correlated with the second/first precipitation PCs, respectively. The summer runoff’s EOF PCs also show significant correlations with the multivariate El Niño–Southern Oscillation index (MEI) of the summer and winter months, while the summer precipitation PCs do not. Statistic analysis shows that EOF1 of runoff and EOF2 of precipitation are related to El Niño, while EOF2 of runoff and EOF1 of precipitation are related to a dipole SST anomaly over the northwestern Pacific. The interdecadal relationship between summer runoff, precipitation, and SST variability is further studied by singular value decomposition (SVD) analysis. Pronounced warming (SST) and drying (runoff) trends in first SVD PCs have been identified. These SVDs are used to reconstruct a decadal anomaly pattern, which produces flooding in part of the Chang Jiang River basin and dryness in the northern EC, consistent with observations. [ABSTRACT FROM AUTHOR]

Heavy monsoon rainfall ravaged a large swath of East Asia in summer 2020. Severe flooding of the Yangtze River displaced millions of residents in the midst of a historic public health crisis. This extreme rainy season was not anticipated from El Niño conditions. Using observations and model experiments, we show that the record strong Indian Ocean Dipole event in 2019 is an important contributor to the extreme Yangtze flooding of 2020. This Indian Ocean mode and a weak El Niño in the Pacific excite downwelling oceanic Rossby waves that propagate slowly westward south of the equator. At a mooring in the Southwest Indian Ocean, the thermocline deepens by a record 70 m in late 2019. The deepened thermocline helps sustain the Indian Ocean warming through the 2020 summer. The Indian Ocean warming forces an anomalous anticyclone in the lower troposphere over the Indo-Northwest Pacific region and intensifies the upper-level westerly jet over East Asia, leading to heavy summer rainfall in the Yangtze Basin. These coupled ocean-atmosphere processes beyond the equatorial Pacific provide predictability. Indeed, dynamic models initialized with observed ocean state predicted the heavy summer rainfall in the Yangtze Basin as early as April 2020. [ABSTRACT FROM AUTHOR]

Air pollution is estimated to contribute to approximately 7 million premature deaths, of which around 4.5 million deaths are linked to ambient (outdoor) air pollution. The deaths attributed to air pollution rank the highest in the Asian region, and thus, the implementation of the stricter World Health Organization (WHO) Global Air Quality Guidelines (AQGs) released on 22 September 2021 will generate the greatest health benefits in the Asian region. Here we present some key messages and recommendations at national, regional, and global levels to promote the strategies for implementation of the ambitious WHO 2021 AQGs in the Asian region. [ABSTRACT FROM AUTHOR]

Two conclusions are obtained by analyzing the fluctuation data of the temperature field and the sound transmission in the South China Sea from ASIAEX 2001 volume interaction experiment. First of all, the peak-to-peak value of the particle vertical mean displacement due to the internal waves exceeds 40 m. Secondly, the peak-to-peak value of the sound transmission fluctuations represented by the pulse leading-edge fluctuations of the travel-time average exceeds 100 ms. Based on that, the major components of the internal waves are obtained by analyzing the spectrum of the temperature field fluctuations. The spectrum structures of the temperature field fluctuations in the across-shelf and the along-shore directions are compared respectively, and the spectrum structures of the sound transmission in such two different directions are also compared. The multi-path signals and the travel- time of the pulse are respectively used to capture the in - formation of the sound transmission fluctuations, and their spectrum structures are compared also. [ABSTRACT FROM AUTHOR]