Number of comments: 4
Comment by: Chunzai Wang
September 4, 2015 - 11:10am
It is well-known that dust can be transported to the Caribbean or northern South America from Africa. Did you look at how the transported dust affects oceanic and atmospheric variables in these regions (the detailed processes)?
Comment by: Santiago
September 9, 2015 - 9:47am
Thanks for your comments and interest in our work.
Although dust transport from Africa to the Caribbean and northern South America is a well known feature of climate variability over the region, this particular event caught our attention since this is the first official report showing large amounts of Saharan dust desposited in central Colombia. Furthermore, the trajectory of this particular transport was located further south than it normaly does during boreal summer. For example, Yu et al. (2015) pointed out that dust transport from Africa to South America (including the Amazon and most of Colombian and Venezuelan territory) is negligible during boreal summer (because the ITCZ is located to the north of this region), but this particular event occurred on late-June. Prospero et al. (2014) suggest similar conclusions.
Addressing your question about the atmospheric and oceanic circulation during this particular event, we identified that the dust trajectory was characterized by the non-occurrence of precipitation (Fig.2). This could favor the transport of large dust concentrations to central Colombia, where the mineral dust was finally deposited. Additionally, meteorological conditions over central Colombia by the time of dust arrival (June 27) were characterized by a very stable atmosphere, consistent with the high temperatures and low air humidity associated to the development of El Niño-like conditions during boreal summer 2014 (Fig. 3). However, local rain gauges in Medellín indicate the ocurrence of rainfall during the night after the dust deposition (June 28). Moreover, the development of El Niño-like conditions by late-June 2014 would favor the southward displacement of this particular dust trajectory. We are currently addressing the possible mechanisms that allowed the deposition of such large dust amounts in a region where this has not been the rule, and the evolution of atmospheric and oceanic variabiles during this event.
Comment by: Joseph Prospero
September 10, 2015 - 12:55pm
The CALIPSO product toward the end of June did show dust over the region although the track was not over your site (it was close). I would suspect that sonde measurements would show a nice dry layer (the Saharan Air Layer - SAL- described by Carlson and Prospero in the 1970s. Normally you would not expect much rain during a strong SAL event because of the sharp inversion. But given your location, and the complex topography, I would suspect that convection events could break up the inversion which could produce rain (and wash out the dust). Have you actually collected rain in this or related studies?
Comment by: Santiago Giraldo
September 10, 2015 - 1:15pm
Thank you for your interest. During the days surrounding the event we had a dry regime, nonetheless we had precipitation at small hours of June 28, just after the event was evidence in the city (all day long on June 27).
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