Diurnal and seasonal variation, intensity, and structure of deep convective systems (DCSs; with 20-dBZ echo tops exceeding 14 km) over the Tibetan Plateau–South Asian monsoon region from the Tibetan Plateau (TP) to the ocean are investigated using 14 yr of Tropical Rainfall Measuring Mission (TRMM) data. Four unique regions characterized by different orography are selected for comparison, including the TP, the southern Himalayan front (SHF), the South Asian subcontinent (SAS), and the ocean. DCSs and intense DCSs (IDCSs; with 40-dBZ echo tops exceeding 10 km) occur more frequently over the continent than over the ocean. About 23% of total DCSs develop into IDCSs in the SHF, followed by the TP (21%) and the SAS (15%), with the least over the ocean (2%). The average 20-dBZ echo-top height of IDCSs exceeds 16 km and 9% of them even exceed 18 km. DCSs and IDCSs are the most frequent over the SHF, especially in the westernmost SHF, where the intensity—in terms of strong radar echo-top (viz., 40 dBZ) height, ice-particle content, and lightning flash rate—is the strongest. DCSs over the TP are relatively weak in convective intensity and small in size but occur frequently. Oceanic DCSs possess the tallest cloud top (which mainly reflects small ice particles) and the largest size, but their convective intensity is markedly weaker. DCSs and IDCSs show a similar diurnal variation, mainly occurring in the afternoon with a peak at 1600 local time over land. Although most of both DCSs and IDCSs occur between April and October, DCSs have a peak in August, whereas IDCSs have a peak in May.

Abstract. The Weather Research and Forecasting Model with chemistry (WRF-Chem model) was used to investigate a typical dust storm event that occurred from 18 to 23 March 2010 and swept across almost all of China, Japan, and Korea. The spatial and temporal variations in dust aerosols and the meteorological conditions over East Asia were well reproduced by the WRF-Chem model. The simulation results were used to further investigate the details of processes related to dust emission, long-range transport, and radiative effects of dust aerosols over the Taklimakan Desert (TD) and Gobi Desert (GD). The results indicated that weather conditions, topography, and surface types in dust source regions may influence dust emission, uplift height, and transport at the regional scale. The GD was located in the warm zone in advance of the cold front in this case. Rapidly warming surface temperatures and cold air advection at high levels caused strong instability in the atmosphere, which strengthened the downward momentum transported from the middle and low troposphere and caused strong surface winds. Moreover, the GD is located in a relatively flat, high-altitude region influenced by the confluence of the northern and southern westerly jets. Therefore, the GD dust particles were easily lofted to 4 km and were the primary contributor to the dust concentration over East Asia. In the dust budget analysis, the dust emission flux over the TD was 27.2 ± 4.1 µg m −2 s −1 , which was similar to that over the GD (29 ± 3.6 µg m −2 s −1 ). However, the transport contribution of the TD dust (up to 0.8 ton d −1 ) to the dust sink was much smaller than that of the GD dust (up to 3.7 ton d −1 ) because of the complex terrain and the prevailing wind in the TD. Notably, a small amount of the TD dust (PM 2.5 dust concentration of approximately 8.7 µg m −3 ) was lofted to above 5 km and transported over greater distances under the influence of the westerly jets. Moreover, the direct radiative forcing induced by dust was estimated to be −3 and −7 W m −2 at the top of the atmosphere, −8 and −10 W m −2 at the surface, and +5 and +3 W m −2 in the atmosphere over the TD and GD, respectively. This study provides confidence for further understanding the climate effects of the GD dust.

Lightning flash activities on the Tibetan Plateau are investigated using observations from the lightning imaging sensor. About 95% of the flashes are found to occur during May to September with a single peak in the summer from June to August. There is substantial lightning activity in May on the plateau, especially on the southern and eastern plateau. The diurnal variation of the lightning activity shows a prominent peak from 1500 to 1700 LT for most of the plateau with earlier activity on the eastern and southern plateau and a delay on the western, northern, and central plateau. Few lightning flashes are observed between 0000 and 1000 LT. The highest flash density is found in the grassland central plateau with a value of 4.5 flashes km−2 yr−1, while the minimum is found in the semiarid western plateau with a value of 1.5 flashes km−2 yr−1. The optical radiance of flashes fits a lognormal distribution. More energetic flashes are found on the mountainous eastern and northern plateau, and weaker flashes are found on the wet southern and semiarid western plateau. A nonlinear relationship between lightning activity and monthly averaged convective available potential energy (CAPE) is found. The flash number per CAPE on the Tibetan Plateau is much larger than it is for other regions with prominent lightning activity (but low altitude).

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Fugitive road dust (FRD) particles emitted by traffic-generated turbulence are an important contributor to urban ambient fine particulate matter (PM2.5). Especially in urban areas of developing countries, FRD PM2.5 emissions are a serious environmental threat to air quality and public health. FRD PM2.5 emissions have been neglected or substantially underestimated in previous study, resulting in the underestimation of modeling PM concentrations and estimating their health impacts. This study constructed the FRD PM2.5 emissions inventory in a major inland city in China (Lanzhou) in 2017 at high-resolution (500 × 500 m2), investigated the spatiotemporal characteristics of the FRD emissions in different urban function zones, and quantified their health impacts. The FRD PM2.5 emission was approximately 1141 ± 71 kg d–1, accounting for 24.6% of total PM2.5 emission in urban Lanzhou. Spatially, high emissions exceeding 3 × 104 μg m–2 d–1 occurred over areas with smaller particle sizes, larger traffic intensities, and more frequent construction activities. The estimated premature mortality burden induced by FRD PM2.5 exposure was 234.5 deaths in Lanzhou in 2017. Reducing FRD emissions are an important step forward to protect public health in many developing urban regions.

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[1] The data from the lightning imaging sensor (LIS), precipitation radar (PR), and passive microwave imaging (TMI) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite from 1998 to 2005 have been used to investigate the lightning activity and precipitation characteristics before and after the onset of the South China Sea (SCS) summer monsoon. The results show that the lightning activity over the SCS begin to enhance in April, peak in May, and decrease after June. Compared to the premonsoon season, mean cell-level flash rate decreased 13% and mean flash optical radiance increased 15% during the monsoon season, respectively. The mean flash rate is higher during the premonsoon season. On the basis of the observations of PR and TMI, it can be found that vertical development of precipitation systems in the premonsoon season was stronger than that in the monsoon season, so frequent lightning activity were observed. Further research indicates that when maximum radar reflectivity at 7 km asl reached 36 dBZ, the probability of lightning occurrence was 50% in the premonsoon season, and it increased to 38 dBZ in the monsoon season. The flash rate of precipitation systems can be expressed as functions of maximum storm top height, maximum snow depth and minimum polarization corrected temperatures (PCTs), respectively. Among those, the most stable one is the relationship between flash rate and maximum snow depth.Citation: Yuan, T., and X. Qie (2008), Study on lightning activity and precipitation characteristics before and after the onset of the South China Sea summer monsoon,