The authors examine the distribution and varia- tion of carbon monoxide （CO） in the tropics from the sur- face to the lower stratosphere. By analyzing space-borne microwave limb sounder （MLS） measurements, measure- ments of pollution in the troposphere （MOPITT） and mod- em-era retrospective analysis for research and applications （MERRA） meteorological products, and atmospheric chemistry and climate model intercomparison project （ACCMIP） surface emission inventories, the influences of atmospheric dynamics and surface emissions are investi- gated. The results show that there are four centers of highly concentrated CO mixing ratio over tropical areas in differ- ent seasons： two in the Northern Hemisphere and another two in the Southern Hemisphere. All of these centers cor- respond to local deep convective systems and mon- soons/anticyclones. The authors suggest that both deep convections and anticyclones affect CO in the tropical tro- posphere and lower stratosphere--the former helping to transport CO from the lower to the middle troposphere （or even higher）, and the dynamical uplift and isolation effects of the latter helping to build up highly concentrated CO in the upper troposphere and lower stratosphere （UTLS）. Similarly, there are two annual surface emission peaks in- duced by biomass burning emissions： one from the North- ern Hemisphere and the other from the Southern Hemi- sphere. Both contribute to the highly concentrated CO mixing ratio and control the seasonal variabilities of CO in the UTLS, combining the effects of deep convections and monsoons. Results also show a relatively steady emission rate from anthropogenic sources, with a small increase mainly coming from Southeast Asia and lndia. These emis- sions can be transported to the UTLS over Tibet by the joint effort of surface horizontal winds, deep convections, and the Asian summer monsoon system.
LI QianSHI Hua-FengSHAO Ai-MeiBIAN Jian-ChunLü Da-Ren
GPS radio occultation data from the Constellation Observing System for Meteorology, Ionosphere, and Climate(COSMIC) mission were used to validate the measurements of the advanced microwave sounding unit-A(AMSU-A) in the lower stratosphere from different satellites. AMSU-A observations from two different calibrations—the pre-launch operational and post-launch simultaneous nadir overpass(SNO) calibrations—were compared to microwave brightness temperatures(Tb)simulated from COSMIC data. Observations from three satellites(NOAA-15,-16, and-18) were used in the comparison. The results showed that AMSU-A Tb measurements from both calibrations and from all three NOAA satellites were underestimated in the lower stratosphere,and that the biases were larger in polar winters, especially over the southern high latitudes. In comparison to operational calibration, the SNO-calibrated AMSU-A data produced much smaller biases relative to the COSMIC data.The improvement due to SNO calibration was quantified by a Ratio index, which measured the bias changes from operational to SNO calibrations relative to the biases between the operational-calibrated AMSU-A data and the COSMIC data. The Ratio values were 70 % for NOAA-15and [80 % for NOAA-18 and-16, indicating that the SNO calibration method significantly reduced AMSU-A biases and effectively improved AMSU-A data quality.
During recent decades, the tropical Indo-Pacific Ocean has become increasingly warmer. Meanwhile, both the northern and southern hemispheric polar vortices （NPV and SPV） have exhibited a deepening trend in boreal winter. Although previous studies have revealed that the tropical Indian Ocean warming （IOW） favors an intensifying NPV and a weakening SPV, how the tropical Pacific Ocean warming （POW） influences the NPV and SPV remains unclear. In this study, a comparative analysis has been conducted through ensemble atmospheric general circulation model （AGCM） experiments. The results show that, for the Northern Hemisphere, the two warmings exerted opposite impacts in boreal winter, in that the IOW intensified the NPV while the POW weakened the NPV. For the Southern Hemisphere, both the IOW and POW warmed the southern polar atmosphere and weakened the SPV. A diagnostic analysis based on the vorticity budget revealed that such an interhemispheric difference in influences from the IOW and POW in boreal winter was associated with different roles of transient eddy momentum flux convergence between the hemispheres. Furthermore, this difference may have been linked to different strengths of stationary wave activity between the hemispheres in boreal winter.
In situ measurements of the vertical structure of ozone were made in Changchun （43.53°N, 125.13°E）, China, by the Institute of Atmosphere Physics, in the summers of 2010-13. Analysis of the 89 validated ozone profiles shows the vari- ation of ozone concentration in the upper troposphere and lower stratosphere （UTLS） caused by cut-off lows （COLs） over Changchun. During the COL events, an increase of the ozone concentration and a lower height of the tropopause are observed. Backward simulations with a trajectory model show that the ozone-rich airmass brought by the COL is from Siberia. A case study proves that stratosphere-troposphere exchange （STE） occurs in the COL. The ozone-rich air mass transported from the stratosphere to the troposphere first becomes unstable, then loses its high ozone concentration. This process usually happens during the decay stage of COLs. In order to understand the influence of COLs on the ozone in the UTLS, statistical analysis of the ozone profiles within COLs, and other profiles, are employed. The results indicate that the ozone concentrations of the in-COL profiles are significantly higher than those of the other profiles between ±4 km around the tropopause. The COLs induce an increase in UTLS column ozone by 32% on average. Meanwhile, the COLs depress the lapse-rate tropopause （LRT）/dynamical tropopause height by 1.4/1.7 km and cause the atmosphere above the tropopause to be less stable. The influence of COLs is durable because the increased ozone concentration lasts at least one day after the COL has passed over Changchun. Furthermore, the relative coefficient between LRT height and lower stratosphere （LS） column ozone is -0.62, which implies a positive correlation between COL strength and LS ozone concentration.
Yushan SONGDaren LUQian LIJianchun BIANXue WUDan LI
