A high resolution satellite view of the aerosol weekly cycle variability over Central Europe

Abstract

In this study, the aerosol weekly cycle patterns over Central Europe are defined, using high resolution aerosol data from TERRA MODIS satellite instrument. A decadal (2/2000-2/2010) high resolution gridded dataset was compiled using MODIS TERRA level-2 data. The general aerosol optical depth (AOD 550nm) weekly patterns were defined at a 0.1°×0.1° resolution using the weekly cycle index (WCI). To remove episodic dust transport events, two different aerosol flags, employing fine mode ratio (FMR 550nm) and AOD 550nm data, were applied diagnostically. The region of interest is Central Europe, which is an area with a recorded aerosol weekly cycle. The main body of the positive (midweek peak) weekly cycle plume extends over the central part of Central Europe with the WCI levels gradually lowering until the weekly cycle becomes negative (weekend peak) when moving away from the main body of the plume. There is not a clear connection between the WCI patterns and topography while there is a correlation between a positive weekly cycle in summer and population density. The use of the two aerosol flags does not change the WCI patterns giving an indication of the continental character of the plume. A clear Monday minimum appears over the regions which are characterized by a high positive WCI. Monday shifts to Tuesday when moving to the East which is indicative of an aerosol transport from the dominating westerly wind flow. The investigation of the WCI and the average percent departure (APD) for the day of weekly maximum/minimum, for 22 stations examined in previous weekly cycle studies, reveals that the weekly cycle is positive and statistically significant for only a few stations situated in France, Germany, Czech Republic and Belgium. The 1°×1° MODIS TERRA data in most cases can give an indication of the local aerosol weekly cycle strength and phase. It is shown here that the satellite derived day of the weekly maximum and minimum is in general in line with results from ground-based studies; however, the weekly variability does not agree with the variability shown in these studies. The investigation of the seasonal WCI and maximum/minimum day patterns reveals that the signal of the positive weekly cycle plume appearing over Central Europe is very strong during summer. The day of maximum AOD 550nm ranges between Wednesday, Thursday and Friday becoming Saturday for the Eastern regions. The day of minimum is Monday for the central parts becoming Tuesday for the Eastern regions. This summer shift of the day of maximum and minimum for regions situated in the Central and Eastern Central Europe is an indication of the transport of the aerosols from the dominating westerly wind flow. Parts of the summer positive weekly cycle plume can be observed in spring and autumn. © 2012 Elsevier B.V.