Analysis of measurements of Saharan dust by airborne and ground‐based remote sensing methods during the Puerto Rico Dust Experiment (PRIDE)

Abstract

For 26 days in mid‐June and July 2000, a research group comprised of U.S. Navy, NASA, and university scientists conducted the Puerto Rico Dust Experiment (PRIDE). In this paper we give a brief overview of mean meteorological conditions during the study. We focus on our findings on African dust transported into the Caribbean utilizing a Navajo aircraft and AERONET Sun photometer data. During the study midvisible aerosol optical thickness (AOT) in Puerto Rico averaged 0.25, with a maximum >0.5 and with clean marine periods of ∼0.08. Dust AOTs near the coast of Africa (Cape Verde Islands and Dakar) averaged ∼0.4, 30% less than previous years. By analyzing dust vertical profiles in addition to supplemental meteorology and MPLNET lidar data we found that dust transport cannot be easily categorized into any particular conceptual model. Toward the end of the study period, the vertical distribution of dust was similar to the commonly assumed Saharan Air Layer (SAL) transport. During the early periods of the study, dust had the highest concentrations in the marine and convective boundary layers with only a weak dust layer in the SAL being present, a state usually associated with wintertime transport patterns. We corroborate the findings of Maring et al. [2003] that in most cases, there was an unexpected lack of vertical stratification of dust particle size. We systematically analyze processes that may impact dust vertical distribution and speculate that dust vertical distribution predominately influenced by flow patterns over Africa and differential advection coupled with fair weather cloud entrainment, mixing by easterly waves, and regional subsidence.

Seasonal variability of aerosol concentration and size distribution in Cape Verde using a continuous aerosol optical spectrometer

“…Long term measurements over the Atlantic to determine Sahara dust transport to the west are difficult to implement. Due to its location on the tropical North Atlantic, off the west coast of Africa, the Cape Verde Islands are particularly suitable to study the transport of Saharan dust plumes to the Atlantic, Caribbean Sea, and Amazon Basin (Prospero et al, 1981;Reid et al, 2003;Muhs et al, 2007). The geographical location of the Cape Verde Islands has attracted a number of important field experiments during the last decades (Jaenicke and Schutz, 1978;Moulin et al, 1997;Caquineau et al, 1998;Ratmeyer et al, 1999;Tanré et al, 2003;Nalli et al, 2005;Ansmann et al, 2009;Assmann et al, 2011;Chen et al, 2011).…”

In situ measurements of desert dust particles above the western Mediterranean Sea with the balloon-borne Light Optical Aerosol Counter/sizer (LOAC) during the ChArMEx campaign of summer 2013

“…Some aircraft observations were also conducted in situ inside dust plumes, but they are expensive and scarce (e.g. Schmid et al, 2000;Dulac and Chazette, 2003;Haywood et al, 2003;Reid et al, 2003a;Formenti et al, 2008;Weinzierl et al, 2009Weinzierl et al, , 2011Chen et al, 2011;Denjean et al, 2016), and were often limited to several micrometres in terms of the particle size range covered and did not explore the same dust plume along its transport. One of the incompletely resolved issues is the evolution of the dust particle size distribution during long-range transport .…”

Impact of long-range transport over the Atlantic Ocean on Saharan dust optical and microphysical properties

“…This feature can 25 be understood as the fingerprint of the occurrence of mineral dust transport from Africa. The AE variability evidenced by the standard deviations is large driven by the changes in aerosol mixture that occur in this area (e.g., Reid et al, 2003). Clean maritime conditions, associated to background values, have low AOD and low AE (Smirnov et al, 2000), but they can be modified by mineral dust outbreaks from African deserts and biomass burning episodes.…”

“…Studies dealing with long-term (e.g., Prospero and Lamb, 2003;Prospero and Mayol-Bracero, 2013) and short-term (e.g., Reid et al, 2003;Colarco et al, 2003;Kaufman et al, 2005;Valle-Díaz et al, 2016) databases show a seasonal dependence in the intensity of the long-range transport, being more intense during boreal summer in the subtropical zone. Within this 10 instantaneous values (every 15 minutes) of spectral AOD at 7 wavelengths in the range 340nm -1020nm (in some cases also 1640nm) and the associated Ångström Exponent (AE) derived in the range 440-870 nm.…”