The May/June 2008 Saharan dust event over Munich: Intensive aerosol parameters from lidar measurements

Abstract

[1] At the end of May 2008 one of the strongest Saharan dust outbreaks ever reached Central Europe. This event gave us the opportunity to extend our series of studies on Saharan dust characterization, which includes measurements near the source (SAMUM-1, Morocco) and in the regime of mid range transport (SAMUM-2, Cape Verde). The optical properties of the aerosol particles as a function of time and height are derived from data of the two Raman depolarization-lidar systems MULIS and POLIS at Munich and Maisach (Germany), respectively. Measurements include the extensive properties of the particles, backscatter coefficient b p and extinction coefficient a p , and the intensive particle properties, linear depolarization ratio d p and lidar ratio S p . All quantities are derived at two wavelengths, l = 355 nm and l = 532 nm. The focus of the study is on the intensive properties, for which we found on average d p = 0.30 at 355 nm and d p = 0.34 at 532 nm. The systematic errors were typically larger than the d p -difference at the two wavelengths. With respect to the lidar ratio, we found S p = 59 sr for both wavelengths, with an uncertainty range between ±4 sr and ±10 sr. These values are quite similar to the results from the SAMUM campaigns. Thus, our results suggest that the intensive optical properties of Saharan dust do not change significantly if the transport time is less than one week. However, more case studies in the far-range regime are required to scrutinize this statement. To further refine conclusions with respect to the wavelength dependence of d p a further reduction of the errors is desired.

Optical properties of long-range transported Saharan dust over Barbados as measured by dual-wavelength depolarization Raman lidar measurements

“…Highest S p values are found during the last observed dust event, indicating an increased amount of dust mixed into the boundary layer. This is in good agreement with the mean δ p values of > 0.1 in the boundary layer during the last observed dust event, clearly identifying dust mixed in the boundary (Freudenthaler et al, 2009); for mid-range transported Saharan dust on 8 days during SAMUM-2 in Cape Verde in 2008 (SAMUM08) ; for longrange transported dust over Central Europe on 3 days in Munich, Germany, in 2008 (EARLINET08) (Wiegner et al, 2011); and for long-range transported Saharan dust over the Caribbean on 13 days during SALTRACE in Barbados in 2013 (SALTRACE13). The error bars denote the systematic errors.…”

“…The wavelength-dependent overall mean values are 0.31 ± 0.01 (532 nm) and 0.25 ± 0.07 (355 nm) for fresh Saharan dust (Freudenthaler et al, 2009) and 0.3 ± 0.01 (532 nm) and 0.25 ± 0.03 (355 nm) for midrange transported Saharan dust . For long-range transported Saharan dust towards Central Europe we found slightly higher values of 0.34 ± 0.02 and 0.30 ± 0.05 at 532 and 355 nm, respectively (Wiegner et al, 2011). In Barbados we find a slightly lower mean δ p value of 0.27 ± 0.01 at 532 nm and a rather constant mean value of 0.26 ± 0.03 at 355 nm.…”

“…Yang et al (2013) assume a shape-induced particle sedimentation from measurements of transported dust with the space-based lidar system onboard the CALIOP satellite mission . Wiegner et al (2011) found an increase of the mean particle linear depolarization ratio at 355 nm of an aged Saharan dust plume over Central Europe compared to values measured in fresh Saharan dust plumes (Freudenthaler et al, 2009;Groß et al, 2011b). Until now the mechanism and magnitude of dust aging have been unknown in addition to whether and how they influence the optical properties of dust.…”

“…However, we see different alterations of the optical properties of long-range transported Saharan dust towards Central Europe and of long-range transported Saharan dust over the Atlantic Ocean towards the Caribbean. We do not see a wavelength (Tesche et al, 2009b); for mid-range transported Saharan dust on 5 days during SAMUM-2 in Cape Verde in 2008 (SAMUM08) ; for long-range transported dust over Central Europe on 3 days in Munich, Germany, in 2008 (EARLINET08) (Wiegner et al, 2011); and for long-range transported Saharan dust over the Caribbean on 10 days during SALTRACE in Barbados in 2013 (SALTRACE13). The error bars denote the systematic errors.…”

“…From these studies possible changes due to transport and aging can be studied. Comparisons with measurements of longrange transported Saharan dust over Central Europe (Wiegner et al, 2011) furthermore enable us to investigate whether not only the transport time but also the transport path has an effect of particle aging. An overview of δ p measurements at 355 and 532 nm is given in Fig.…”