Because of its unique location directly in the path of dust storms driven by harmattan winds blowing from the northeast across the Sahara Desert and out across the North Atlantic ocean, Cape Verde is an important site for monitoring aerosols. The AERONET project, managed by NASA's Goddard Space Flight Center, maintains a sun photometer on the island of Sal (the site of Cape Verde's international airport).

In the spring of 2002, Ana Cristina Ferro Marques, now Cape Verde's GLOBE Country Coordinator, started collecting sun photometer data. The figure shows some comparisons between GLOBE and AERONET data. The GLOBE site is at Praia, Cape Verde's capital, about 200 km south of Sal. So, it is not obvious that measurements from these two sites should agree.

We considered the first set of data, from early April, to be "training" data, for the purpose of learning the aerosol protocol. However, the low AOT values agree reasonably well with the AERONET data.

The next set of measurements, in mid-May, are interesting because they were made during a major dust event of Cape Verde. This storm covered a very large area -- the measurements made in Praia are in excellent agreement with the AERONET data. This agreement continued through the end of May.

The third dust event occurred in early June. Here, there are some significant differences in the timing of the AOT values, but not in the magnitude of the values. These results suggest that there may have been a north-to-south movement of a dust cloud over Cape Verde.