Transport of the Saharan dust air plumes over the tropical North Atlantic from FORMOSAT–3/COSMIC observation

摘要

Long–range transport of the Saharan dust plumes during May–August of each year is a prominent feature over the tropical North Atlantic. Observations of temperature profiles are highly desirable in clarifying the impacts of the Saharan dust plumes over the tropical North Atlantic. In this work we evaluate positive temperature anomalies (inversions in the lower troposphere) in the North Atlantic low troposphere originating from Western Africa, and to examine the correspondence of these events to Saharan dust plumes, using several temperature sources and satellite–detected measurements of Aerosol Index. We combine profiles of temperature observations from FORMOSAT–3/COSMIC (F3C) with aerosol observations from Ozone Monitoring Instrument (OMI) to provide direct evidence of the Saharan dust plumes modifying environmental stability. The F3C observations show good profile measurements compared with the radiosondes in the lower troposphere, with the average temperature differences less than 0.5 K. The F3C results were also compared with the Aqua Advanced Infrared Radiation Sounder (AIRS) and meteorological analyses from the National Centers for Environmental Predictions (NCEP), the United Kingdom Met Office (UKMO), and the European Centre for Medium Range Weather Forecast (ECMWF). Our results show that hot air plumes are associated with the Saharan dust plumes during their transport across the tropical North Atlantic. There were eleven distinctive hot air plumes during May–August 2007 and 2008, respectively. These hot air plumes increase environmental temperatures below 5–km altitudes, with the maximum increase of 1–2 K around 2–km. This leads to increase of environmental stability below 2–km altitudes and decrease of environmental stability between 2– and 5–km altitudes. By changing the vertical distribution of environmental stability, the Saharan dust plumes act to stabilize environmental air below 2–km while destabilize environmental air from 2– to 5–km altitudes. These results are distinctively presented in the F3C and AIRS observations but less obvious in the meteorological analyses.