Ozone vertical variations during a typhoon derived from the OMI observations and reanalysis data

Factors dominating 3-dimensional ozone distribution during high tropospheric ozone period

Data from an in situ monitoring network and five ozone sondes are analysed during August of 2012, and a high tropospheric ozone episode is observed around the 8th of AUG. The Community Multi-scale Air Quality (CMAQ) model and its process analysis tool were used to study factors and mechanisms for high ozone mixing ratio at different levels of ozone vertical profiles. A sensitive scenario without chemical initial and boundary conditions (ICBCs) from MOZART4-GEOS5 was applied to study the impact of stratosphere-troposphere exchange (STE) on vertical ozone. The simulation results indicated that the first high ozone peak near the tropopause was dominated by STE. Results from process analysis showed that: in the urban area, the second peak at approximately 2 km above ground height was mainly caused by local photochemical production. The third peak (near surface) was mainly caused by the upwind transportation from the suburban/rural areas; in the suburban/rural areas, local photochemical production of ozone dominated the high ozone mixing ratio from the surface to approximately 3 km height. Furthermore, the capability of indicators to distinguish O₃-precursor sensitivity along the vertical O₃ profiles was investigated. Two sensitive scenarios, which had cut 30% anthropogenic NO_X or VOC emissions, showed that O₃-precursor indicators, specifically the ratios of O₃/NOy, H₂O₂/HNO₃ or H₂O₂/NO_Z, could partly distinguish the O₃-precursor sensitivity between VOCs-sensitive and NOx-sensitive along the vertical profiles. In urban area, the O₃-precursor relationship transferred from VOCs-sensitive within the boundary layer to NOx-sensitive at approximately 1-3 km above ground height, further confirming the dominant roles of transportation and photochemical production in high O₃ peaks at the near-ground layer and 2 km above ground height, respectively.

Lateral Boundary of Cirrus Cloud from CALIPSO Observations

Due to the thinness and small scale of cirrus clouds, its lateral boundary may be missed by conventional passive remote-sensing techniques and climate models. Here, using satellite observations in June–August from 2006 to 2011, a global dataset for the cirrus cloud lateral boundary (CCLB) was established. The results indicate that the optical properties, such as the lidar backscatter, the depolarization ratio and the optical depth, sharply decrease from cloudy regions to clear-sky regions. There are significant regional differences in optical properties and height and thickness of the CCLB. Based on a quantitative estimation, the strongest longwave warming effects (>0.3 W m⁻²) are found near the Equator and over tropical continents. The global average longwave warming effect of the CCLB is at least 0.07 W m⁻², which is much larger than some of the radiative forcings considered in the Intergovernmental Panel on Climate Change (IPCC) reports. Specifically, the CCLB in traditional “clear-sky” region may be totally missed by current models and IPCC reports, which contributes 28.25% (~0.02 W m⁻²) of the whole CCLB radiative effect, twice greater than contrail effect. It is recommended that the CCLB effect should be taken account in future climate models and the next IPCC reports.