Mechanisms for the Intraseasonal Variability of Tropospheric Ozone during the Indian Winter Monsoon
R. B. Chatfield1, A. M. Thompson2, H. Guan1, H.J.G. Smit3
1NASA Ames Research Center
2 Pennsylvania State University, Meteorology Dept.
3 Forschungszentrum Jülich
Submitted March 6, 2006
Abstract
We synthesize daily sonde (vertical) information and daily satellite (horizontal) information to provide an empirical description of ozone origins over the northern Indian Ocean during the INDOEX field campaign (February- March 1999). This area is shown to be a significant portion of the “high-ozone
tropics.” East-west O3 features and their flow are identified, and ozone origins
are compared to other tropical regions, using water vapor as a second tracer. In
the study period, multiple processes contribute to O3 column enhancements,
with importance varying strongly by latitude: (a) Low-altitude O3 pollution over
the northern Indian Ocean mainly originates from the Indian subcontinent, and
is traceable to high emission areas; convective activity south of Sri Lanka helps
direct ozone outflow from the Northern Indian Subcontinent; (b) Middle
tropospheric O3 maxima over the Northern Indian Ocean originate from various
sources, often transitioning within a few hours. Convective venting of Asian
pollutants can add 20–50 ppbv to the middle troposphere at 5–10N, alternating
with stratospheric influence. (c) A number of cases suggest that strong mixing-in
of stratospheric air along the subtropical jet raised tropospheric O3 in early
March by ~40–50 ppbv, especially poleward of ~10°N. (d) Influences of lightning
and large-scale biomass burning were not strong during this period, in contrast
to the situation in Africa and the South Atlantic or locally in Southeast Asia. This
work illustrates successes and limitations in approaches to synthesizing
disparate information on trace-gas distributions taken from satellite retrieval
products and ozonesondes.