Chemical evidence of inter-hemispheric air mass intrusion into the Northern Hemisphere mid-latitudes.

The East Asian Summer Monsoon driven by temperature and moisture gradients between the Asian continent and the Pacific Ocean, leads to approximately 50% of the annual rainfall in the region across 20-40°N. Due to its increasing scientific and social importance, there have been several previous studies on identification of moisture sources for summer monsoon rainfall over East Asia mainly using Lagrangian or Eulerian atmospheric water vapor models. The major source regions for EASM previously proposed include the North Indian Ocean, South China Sea and North western Pacific. Based on high-precision and high-frequency 6-year measurement records of hydrofluorocarbons (HFCs), here we report a direct evidence of rapid intrusion of warm and moist tropical air mass from the Southern Hemisphere (SH) reaching within a couple of days up to 33°N into East Asia. We further suggest that the combination of direct chemical tracer record and a back-trajectory model with physical meteorological variables helps pave the way to identify moisture sources for monsoon rainfall. A case study for Gosan station (33.25°N, 126.19°E) indicates that the meridional transport of precipitable water from the SH accompanying the southerly/southwesterly flow contributes most significantly to its summer rainfall.

Comparison of scan-angle method and convective cloud differential method in retrieving tropospheric ozone from TOMS.

Tropospheric ozone, derived from the Scan-Angle Method (SAM) and the Convective Cloud Differential (CCD) method, exhibits a noticeable abundance over the South Atlantic, where it is associated with biomass-burning in the austral spring. This feature is also seen in the distribution of carbon monoxide observed from Measurements Of Pollution In The Troposphere (MOPITT). In the boreal burning season, however, the distribution of the results from SAM and MOPITT-CO present an enhancement related to the biomass-burning over North Africa that does not appear in the CCD results. The relationship of the results from SAM and MOPITT-CO is better than those of the results from the CCD and MOPITT-CO for the December-February period. Conversely, the latter relationship is better than the former for the October-November period. The two methods, SAM and CCD, show higher correlation in the southern burning season, but lower correlation in the northern burning season. The influence of biomass burning on ozone amounts is clearly seen in the SAM results of the elevated ozone over northern equatorial Africa during the northern burning season, but is not present in the CCD results.