Erin Robinson, Alan Pinkert June, 2010 Vertical Characterization of Aerosol over the U.S. - Aeronet, MODIS AOT Erin Robinson, Alan Pinkert June, 2010

Activities Begin comparing MODIS to Aeronet standard AOT Comparing trends in Aeronet station patterns along similar latitudes

Varied Cursor Box Size and Statistic (GSFC) .1 Deg x .1 deg .5 Deg x .5 deg 1 Deg x 1 deg Need to find MODIS cursor box size and statistical aggregation that most closely approximated Aeronet MODIS is a grid dataset and Aeronet is a point dataset. Chose to vary the cursor box from .1 deg x .1 deg (resolution of MODIS) to 2 deg x 2deg Varied statistical aggregation for 5th percentile, 60th percentile and 95th percentile.

Results: We saw that some sites had no correlation between MODIS and Aeronet. For the sites that did have correlation – we saw no major variation between .1 and 1 deg. Others who have done MODIS-Aeronet comparisons chose a .5 deg box Since we didn’t see any major variation, we chose a .5 deg box for our analysis.

Seasonal Comparison – Annual R2 (Blue low; Red ~1) Slope (yellow =1; Red > 1) Over the U.S. we looked at the correlation and slope for annual and seasonal comparison the Winter (DJF), Spring (MAM), Summer (JJA) and Fall (SON). Annual correlation smears the systematic differences that MODIS has during different seasons Compared the R2 value for how ‘repeatable’ the measurement was The slope of the scatter plot indicates how close the Modis measurement is to Aeronet standard overall Good correlation on East and NW MODIS approxmates most sites well (yellow paddles (slope = .8-1); Overestimates in west

Seasonal Comparison – Winter R2 (Blue low; Red ~1) Slope (yellow =1; Red > 1) Over the U.S. we looked at the correlation and slope for annual and seasonal comparison the Winter (DJF), Spring (MAM), Summer (JJA) and Fall (SON). Annual correlation smears the systematic differences that MODIS has during different seasons Low correlation at all sites MODIS approxmates most sites well (yellow paddles (slope = .8-1); Overestimates in west

Seasonal Comparison – Summer R2 (Blue low; Red ~1) Slope (yellow =1; Red > 1) Over the U.S. we looked at the correlation and slope for annual and seasonal comparison the Winter (DJF), Spring (MAM), Summer (JJA) and Fall (SON). Annual correlation smears the systematic differences that MODIS has during different seasons Good correlation on East and NW MODIS approxmates most sites well; Overestimates in west The Walker Branch site shows good correlation, but slope is underestimated – this could be a systematic error that could be fixed

Troposheric Aerosol Aerosol in the troposphere at a constant latitude has the same composition Looking at Aeronet cycle views over for sites in a similar latitude to determine if there are any consistent patters Patterns between multiple sites mean that the aerosol is likely in troposphere and not on the surface.

Southwest U.S. January to April Peak