TRANSPORT AND DISPERSION PATTERNS OF AEROSOLS OVER THE EAST AFRICAN REGION MBITHI D, M., MUTHAMA, J. N., OUMA, G. O., OPIJAH, F. O June 3, 2016 THE WORLD WEATHER OPEN SCIENCE CONFERENCE

PRESENTATION OUTLINE  Introduction  Area of Study  Climate Controls  Data  Methodologies  Analysis  Conclusion June 3, 2016The World Weather Open Science Conference 20142

INTRODUCTION  Aerosols are tiny particles suspended in the atmosphere and can be in the solid phase or in the liquid phase  They have the capacity to cool or warm the surface, favor or inhibit the formation of clouds depending upon their size, type and location, and, if inhaled, some aerosols are harmful to people’s health (Platnick and Hubanks, 2009)Platnick June 3, 2016The World Weather Open Science Conference 20143

 Increasing aerosol concentrations worldwide have appreciable effects on air quality, visibility and local, regional and global climates (Ramanathan et al., 2007)  Simulation of the transport and dispersion patterns of AOD during different seasons of the year helps to identify the possible sources and sinks of the aerosols June 3, 2016The World Weather Open Science Conference 20144

Area of Study  The topographical features are complex and include Great Rift Valley, the East African highlands, mountains and plateaus (Adapted from Obara, A. D., 2003) June 3, 2016The World Weather Open Science Conference 20145

Climate controls  The climates of the East African region are controlled by the:  Inter-Tropical Convergence Zone (ITCZ) (Kiangi et al, 1981; Ininda, 1995; Okoola, 1996)  The Sub-Tropical Anticyclones (Anyamba, 1984).  the Tropical Monsoons (Findlater, 1969; 1971; Okoola, 1996)  Low-Level Cross-Equatorial Jet (Somali Current) (Findlater 1969, 1971; Kinuthia, 1991)  and Mesoscale systems (Ogallo, 1988) June 3, 2016The World Weather Open Science Conference 20146

Schematic of general patterns of winds, pressure and convergence over the East African region  JJA Season: The dominant mean wind flow is South easterly  DJF Season: The dominant mean wind flow is North easterly June 3, 2016 The World Weather Open Science Conference

DATA (AOD & GRIDDED WIND)  The monthly long term means (LTM) of AOD data at 550nm in 1º Χ 1º grid resolution from the MODIS Terra satellite were used  Web-based trajectory model software from the NOAA known as HYSPLIT_4 was used to compute backward and forward air parcel trajectories (Draxler, R.R. and Rolph, G.D., 2003)  Backward and forward air trajectories were calculated for 2 days (48 hours) in order to limit errors due to uncertainties, Harris et al (2005) June 3, 2016The World Weather Open Science Conference 20148

Methodologies The methodologies used to achieve the objectives of the study can be classified into three categories namely:  graphical (Hovmöller analysis)  statistical (e.g. Single mass Curves, Time series, Weighted mean and Std dev. among others)  and numerical methods (trajectory Analysis) June 3, 2016The World Weather Open Science Conference 20149

Global & Regional spatial patterns of MODIS Terra AOD at 550nm  Large land masses contribute most of dust and carbon related aerosols to the atmosphere compared to water masses  Therefore, the northern hemisphere has more regions with high AOD values compared to the southern hemisphere June 3, 2016The World Weather Open Science Conference

Mean monthly AOD amounts around the world based on observations from the MODIS on NASA’s Terra satelliteTerra  February 2008  July 2008 June 3, 2016The World Weather Open Science Conference

Analysis Monthly means for MODIS Terra AOD at 550nm  The analysis was done from February 2000 to December 2008  It can be seen that there is a bimodal pattern in the distribution of AOD throughout the year June 3, 2016The World Weather Open Science Conference

 The higher peak occurring in July and August is as a result of the fact that the south easterly winds that dominate the region of study are well organized  The region is, also, generally under an inversion condition for a long period, that is, June, July and August  This inversion condition does not support upward movement of air resulting to high aerosol concentrations at the lower levels of the atmosphere June 3, 2016The World Weather Open Science Conference

 During the rainy months of March, April and May (MAM) and October, November and December (OND), it can be clearly noted that the AOD values are extremely low  This is due to cloud formation processes and wet deposition  Wet deposition is the removal of air pollution components by the action of rain June 3, 2016The World Weather Open Science Conference

 Topography is one of the parameters to be considered in the air quality studies  Surrounding topography restricts the transport of pollution away from an urban or a rural area June 3, 2016The World Weather Open Science Conference

 When a weak background synoptic circulation combines with a valley, air temperature inversion and surrounding orographic blockade, the result is often a lack of dispersion of significant lower atmospheric pollutants away from the area (Berman et al., 1995; Lu and Turco, 1995; Ellis et al., 2000) as it is the case in this study  The mesoscale wind systems over those areas contribute towards enhanced AOD values found there June 3, 2016The World Weather Open Science Conference

 Three case studies of areas seen to have high AOD values were conducted to determine aerosol sources and sinks over the East African region  These regions were 2°S, 40ºE; 4°N, 36ºE and 2ºS, 30ºE  Two-day (48-hours) backward and forward air trajectories starting at height of 500m (red), 1500m (blue) and 3000m (green) above the ground level (AGL) were computed for 6-hour intervals in each of the three case studies June 3, 2016The World Weather Open Science Conference

 HYSPLIT_4 (version 4) model was used in the analysis  In this model, it is assumed that the aerosols follow the air trajectory along the direction of the wind June 3, 2016The World Weather Open Science Conference

Backward and Forward air trajectory plot for location 2ºS, 40ºE for 48 hours for 20 th February and July 2008 respectively June 3, 2016The World Weather Open Science Conference

Backward and Forward air trajectory plot for location 4ºN,36ºE for 48 hours for 20 th February and July 2008 respectively June 3, 2016The World Weather Open Science Conference

Backward and Forward air trajectory plot for location 2ºS,30ºE for 48 hours for 20 th February and July 2008 respectively June 3, 2016The World Weather Open Science Conference

CONCLUSION  The findings of this study suggested that long distance transport and dispersion of aerosols through low level winds, 1.4 km and below, is responsible for the aerosols affecting the East African region  The transport and dispersion patterns of aerosols greatly depend on the season of the year together with the prevailing atmospheric conditions June 3, 2016The World Weather Open Science Conference

Near Future Plans A PhD in Climate Change with a bias either in:  Air pollution  Remote Sensing  Water OR  Agriculture June 3, 2016The World Weather Open Science Conference

SHUKRANI (Thank you) June 3, 2016 THE WORLD WEATHER OPEN SCIENCE CONFERENCE