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In order to investigate the variations of cloud and aerosol vertical profiles over the Tibetan Plateau (TP) in winter, we performed ground-based lidar observations in Lhasa, a city on the TP, from November 2021 to January 2022. The profiles of extinction coefficient, depolarization ratio, and signal-to-noise ratio (SNR) were retrieved using the atmospheric echo signals collected by the lidar. Clouds were identified by the range-correction echo signals and classified into water clouds, mixed clouds, horizontally oriented ice crystal clouds (HOICC), and ice clouds by the depolarization ratio and the hourly temperature from the European Centre for Medium-Range Weather Forecasts Reanalysis version 5 (ERA5). The clouds mainly appeared at a height of 3~5 km from 14:00–22:00 Beijing Time throughout the field campaign. The height and frequency (~30%) for cloud appearance were significantly lower than that reported in previous studies in summer. The cloud categories were dominated by mixed clouds and ice clouds during the observation period. The proportions of ice clouds gradually increased with increasing heights. After eliminating profiles influenced by clouds, the aerosol extinction coefficient and depolarization ratio were obtained, and the atmospheric boundary layer height (ABLH) was calculated. The aerosol extinction coefficient decreased with increasing height in the ABLH, and there were no obvious changes for the aerosol extinction coefficient above the ABL. The aerosol extinction coefficients near the Earth's surface presented two peaks, appearing in the morning and evening, respectively. The high aerosols at the surface in the morning continually spread upward for 4–5 h and finally reached an altitude of 1 km with the development of ABLH. In addition, the depolarization ratio of aerosols decreased slowly with increasing altitudes. There was no obvious diurnal variation for depolarization ratios, indicating partly that the source of aerosols did not change significantly. These results are beneficial in understanding the evolution of cloud and aerosol vertical profiles over the TP. [ABSTRACT FROM AUTHOR]

Balloon sounding with the Compact Optical Backscatter Aerosol Detector (COBALD) and Frost Point hygrometers (FPs) provides in situ data for a better understanding of the vertical distribution of cirrus clouds. In this study, eight summer balloon‐borne measurements in Kunming (2012, 2014, 2015, and 2017) and Lhasa (2013, 2016, 2018, and 2020) over the Tibetan Plateau were used to show the distribution characteristics of cirrus clouds. Differences of cirrus occurrence were compared by different indices: the backscatter ratio (BSR) at a 455 nm/940 nm wavelength (BSR455 > 1.2/BSR940 > 2), the color index (CI > 7), and the relative humidity with respect to ice (RHice > 70%). Analysis of the profiles indicated that BSR455 > 1.2 was the optimal criterion to identify the cirrus layer and depict the distribution of the CI and RHice within cirrus clouds. The results showed that the median CI (RHice) within the cirrus clouds at both sites was mostly in the 18–20 (90%–110%) range at pressures below 120 hPa. Furthermore, the balloon‐borne measurements combined with Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) measurements indicated a high frequency of cirrus occurrence near the tropopause in Kunming and Lhasa. The top height of cirrus occurrence at both sites was above the cold point tropopause and the lapse rate tropopause. Both Kunming and Lhasa had the highest frequency of thin cirrus clouds in the 0–0.4 km vertical cirrus thickness range. Plain Language Summary: Balloon‐borne measurements of cirrus clouds are scarce over the Tibetan Plateau. The sounding water vapor, ozone, and particles (SWOP) campaign has collected Compact Optical Backscatter Aerosol Detector (COBALD) and Frost Point Hygrometers (FPs) data for eight summers in Kunming and Lhasa. The backscatter ratio at wavelengths of 455 and 940 nm (BSR455, BSR940) from COBALD, the color index (CI), and the relative humidity over ice (RHice) from the FPs are able to indicate the occurrence of cirrus clouds. BSR455 >1.2/BSR940 > 2 was the optimal criterion to identify the cirrus layer in the upper troposphere over the Tibetan Plateau. The results showed that the CI and RHice within the cirrus clouds at both sites have a consistent distribution. The median CI (RHice) remained essentially in the range of 18–20 (90%–110%) below 120 hPa. The top height of cirrus occurrence at both sites was above the cold point tropopause and the lapse rate tropopause. Thin cirrus clouds (less than 400 m thick) had the highest frequency in both Kunming and Lhasa. Key Points: A backscatter ratio over 1.2/2 at a 455 nm/940 nm wavelength can effectively identify cirrus clouds over the Tibetan PlateauCirrus clouds were observed above the cold point tropopause (CPT) in both Kunming and LhasaAbout 38% (39%) of the cirrus clouds are thinner than 400 m in Kunming (Lhasa) [ABSTRACT FROM AUTHOR]

Environment context: One-year-long on-line measurements of surface O3 and CO mixing ratios were performed on the southeast Tibetan Plateau to examine O3 behaviour. During the daytime, the O3 mixing ratio was strongly affected by vertical air exchange. The O3 mixing ratio was high in the afternoon and decreased at night, indicating a sink of tropospheric O3. The upper limit of the tropospheric O3 sink averaged from 4.5 to 5.5 ppb h−1. Rationale: Ozone (O3) behaviour over the Tibetan Plateau has attracted attention in recent decades. However, few long-term measurements have been performed in the region. Methodology: Field observations were conducted at a mountain site on the southeastern Tibetan Plateau from June 2014 to July 2015 in order to understand the behaviour of surface O3 and its influencing factors. Backward trajectory cluster analysis was applied to understand long-range transport sources and their relative contributions. Results: The monthly average O3 ranged from 22.1 to 48.6 ppb with a common high spring ozone concentration phenomenon. The O3 diurnal variation exhibited a similar pattern to those in polluted areas but the cause was different. The O3 mixing ratio was significantly positively correlated with mixed-layer depth and wind speed, and negatively with temperature and relative humidity, indicating strong vertical air exchange. Approximately 50% of air mass trajectories originated from the northeastern Bengal Bay region, with fairly low O3 (CO) mixing ratios and high humidity. Others originated from the north Indian subcontinent (28%) and the Middle East (18%), with fairly high O3 (and CO) and low humidity. Discussion: The average relative contributions of different air masses to surface O3 and CO were small and scattered but large for trajectories arriving at 14:00 hours when vertical air exchange was close to its strongest for the day. The tropospheric O3 sink may be common in the highlands, indicating a negative greenhouse effect there. The O3 sink at Linzhi was estimated in the range of 4.5–5.5 ppb h−1 at maximum. Summary. One-year-long on-line measurements of surface O3 and CO mixing ratios were performed on the southeast Tibetan Plateau to examine O3 behaviour. During the daytime, the O3 mixing ratio was strongly affected by vertical air exchange. The O3 mixing ratio was high in the afternoon and decreased at night, indicating a sink of tropospheric O3. The upper limit of the tropospheric O3 sink averaged from 4.5 to 5.5 ppb h−1. [ABSTRACT FROM AUTHOR]

We present validation studies of MLS V2.2 and V3.3 water vapor (WV) and ozone profiles over the Tibetan Plateau (Naqu and Lhasa) and its adjacent region (Tengchong) respectively by using the balloon-borne Cryogenic Frost point Hygrometer and Electrochemical Concentration Cell ozonesonde. Coincident in situ measurements were selected to compare the MLS V2.2 and V3.3 WV and ozone profiles for understanding the applicability of the two version MLS products over the region. MLS V2.2 and V3.3 WV profiles respectively show their differences within −2.2±15.7% ( n=74) and 0.3±14.9% ( n=75) in the stratosphere at and above 82.5 hPa. Accordingly, at 100 hPa, the altitude approaching the tropopuase height, differences are within 9.8±46.0% ( n=18) and 23.0±45.8% ( n=17), and they are within 21.5±90.6% ( n=104) and 6.0±83.4% ( n=99) in upper troposphere. The differences of MLS ozone are within −11.7±16.3% ( n=135, V2.2) and 15.6±24.2% ( n=305, V3.3) at and above 82.5 hPa. At 100 hPa, they are within −3.5±54.4% ( n=27) and −8.7±41.6% ( n=38), and within 18.0±79.1% ( n=47) and 34.2±76.6% ( n=160) in the upper troposphere. The relative difference of MLS WV and ozone profile has significant oscillation and scatter at upper troposphere and lower stratosphere partly due to the stronger gradients of WV and ozone concentrations here as well the linear interpolation of sonde data for the intercomparison. At and below 70 hPa, the relative differences of MLS ozone are significantly larger over Lhasa during the Tibetan Plateau 'ozone valley' season, which is also the Asian Summer Monsoon period. The MLS ozone differences over the three sites are similar in their vertical distributions during that period. A simple linear correlation analysis between MLS and sonde profiles indicates that the sensitivity of MLS profile products is related to concentrations at each pressure level. The MLS V3.3 product sensitivity is slightly improved for WV at and above 82.5 hPa, whereas it is not obvious for ozone. The possible factors contributing to the differences of the MLS profile products of WV and ozone are discussed. [ABSTRACT FROM AUTHOR]

10Be/7Be is a stratospheric sensitive tracer. In this paper, measurements of 10Be/7Be and surface O3 from October 2005 to May 2006 at Mt. Waliguan (hereafter WLG, 100.898°E, 39.287°N, 3810 m, a.s.l.), China global atmospheric watch (GAW) observatory, are introduced and used to investigate the stratosphere-troposphere transport (STT) and its impact on surface O3 on the Tibetan Plateau. The results show that the magnitude of STT is weak in winter, followed by strengthening from the end of winter to 10 7 10 7 the middle of spring (from mid February to mid April) with large increases in Be, Be, Be/ Be and surface O3. At the end of spring (from the end of April to mid May in this paper), the STT weakened, and the continuous increase of surface O3 at WLG is produced by tropospheric photochemistry reactions. [ABSTRACT FROM AUTHOR]