Motivation. Objectives

Transcription

1 Motivation It is thought that large dust events from the Bodele Depression might be linked to epidemics in the Meningitis Belt ; a region of the Sahel in Africa plagued by the meningitis disease. Objectives Tamara L. Battle M.S., Dept. of Earth & Atmospheric Sciences The City College of New York, CUNY Advisor: Dr. Edward Hindman, CCNY Mentor: Dr. Lynn Sparling, UMBC Is it possible to determine the altitude of the dust layer from its horizontal movement? Can the large dust signals seen in the Sahel be tracked back to the Bodele Depression as the source? Investigation of the frequency and intensity of dust episodes originating in the Bodele Depression and the transport characteristics of atmospheric dust out of this region, using: African Meningitis Belt Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) retrievals; Aerosol Robotic Network (AERONET) AOT measurements; NASA/GSFC Trajectory Model using the National Centers for Environmental Protection (NCEP) Reanalysis winds, initialized at the 500mb, 700mb and 850mb pressure levels. Global Surface Winds Mean January prevailing surface winds and centers of atmospheric pressure, During this time, the ITCZ (intertropical convergence zone, represented as a red line) is located below the equator, and conditions in northern Africa are dry (October May). Bodele Depression 17 N, 17 E Mean July prevailing surface winds and centers of atmospheric pressure, At this time of year, the ITCZ moves above the equator, bringing about the rainy season in northern Africa (June September). Areas with Frequent Epidemics of Meningococcal Meningitis, 2002 AERONET site 1

2 Primary Sources of Atmospheric Dust Map of Chad, Africa Gobi North American Saharan Turkestan Australian Atacama Patagonian Namib Arabian Image reference: Griffin, D. W., C. A. Kellogg, et al. (2002). "The Global Transport of Dust: An intercontinental river of dust, microorganisms and toxic chemicals flows through the Earth s atmosphere." American Scientist 90(3). How Dust Moves Aeolian (or Eolian) transportation - the process whereby surface dust particles are picked up and transported by the wind. Aeolian dust transport can occur through creep, saltation, or suspension of the dust particles. Dust from a sandstorm in north-central Africa, as it fills the air over the country of Chad. 2

3 Bodele Depression 17 N, 17 E Aerosol optical thickness measurements, Bondoukoui site, Burkina Faso. TOMS-AI image, highlighting the Bodele Depression source region, Chad, Africa, 23 May, The image, chosen to correspond with the AOT peak measurement from Bondoukoui AERONET site, depicts mildly elevated aerosol index levels over the Bodele Depression. A series of TOMS-AI images for the period 2 March 5 March, Images show the progression of a dust event as it moves across North Africa toward the Atlantic Ocean. 3

4 X Image of TOMS Aerosol Index measurements, 3 March - 8 March, 1997 (the numbers above each image corresponds to the Julian Day of the year; for example, Day 62 = 3 March 1997, and so forth). Composite image of TOMS Aerosol Index and trajectory simulation results, 3 March - 8 March,

5 Trajectory modeling results at altitudes = 1.5km (red), 3km (green), and 5.6km (blue), beginning 2 March, 1997 (Julian Day 61) through 7 March, 1997 (Julian Day 66). Trajectory modeling results, 3 March, 1997 (Julian Day 62) through 8 March, 1997 (Julian Day 67). Trajectory modeling results, 4 March, 1997 (Julian Day 63) through 9 March, 1997 (Julian Day 68). Trajectory modeling results, 5 March, 1997 (Julian Day 64) through 10 March, 1997 (Julian Day 69). 5

6 X Image of TOMS Aerosol Index measurements, 3 March - 8 March, 1997 (the numbers above each image corresponds to the Julian Day of the year; for example, Day 62 = 3 March 1997, and so forth). Back trajectory modeling results, 5 March, 1997 (Julian Day 64) to 28 February, 1997 (Julian Day 59). A series of TOMS-AI images for the period 30 May 4 June, Images show the progression of a dust event as it moves across North Africa toward the Atlantic Ocean. 6

7 Trajectory modeling results at altitudes = 1.5km (red), 3km (green), and 5.6km (blue), beginning 30 May, 1997 (Julian Day 150) through 4 June, 1997 (Julian Day 155). 7

8 Trajectory modeling results, 31 May, 1997 (Julian Day 151) through 5 June, 1997 (Julian Day 156). Trajectory modeling results, 1 June, 1997 (Julian Day 152) through 6 June, 1997 (Julian Day 157). Trajectory modeling results, 2 June, 1997 (Julian Day 153) through 7 June, 1997 (Julian Day 158). Trajectory modeling results, 3 June, 1997 (Julian Day 154) through 8 June, 1997 (Julian Day 159). 8

9 Back trajectory modeling results, 5 June, 1997 (Julian Day 156) to 31 May, 1997 (Julian Day 151). An example of dust clouds generated by strong winds in a large sandstorm in north central Africa Meningococcal Meningitis Quick Facts Conclusions and Future Work Additional case studies have been analyzed for the years : Transmitted via close contact with infected person(s) through airborne particles Incubation period of ~4 days (range from 2-10) Highest incidences in Burkina Faso, Ethiopia, Niger and Chad (World Health Organization) Results from these analyses indicate a strong dependence of horizontal transport with the assumed vertical location of dust particles in the atmospheric column, and seasonal variations associated with the meteorology and climatology of the region. Uncertainties include: Differentiation of atmospheric aerosols (i.e., dust, biomass burning, etc.) Limitations of TOMS in detecting aerosol below ~2 km boundary Accuracy in back-trajectory modeling to determine source Statistical analyses will be performed to calculate the frequency of dust events and the percentage that can be traced back in time to the Bodele Depression as the source of the emissions. 9

10 Acknowledgements CCNY/NOAA-CREST Fellowship Program UMBC/Joint Center for Earth Systems Technology NASA/GSFC Code 916: Atmospheric Chemistry and Dynamics Branch Others 10