Special Observing Periods (SOP) and instruments

1. the dry phase (phase 0) lasting from November to February;
2. the onset phase (phase 1) leading to the monsoon jump (end of June);
3. the well developed monsoon (phase 2: peak of the rainy season over the Sahel, and little dry season on the coast) from the end of June to mid-September;
4. the period most favourable for the tropical cyclogenesis over the Atlantic, lasting from mid-August to mid-October.

This latter period is not a monsoon phase per se and it overlaps phase 2. It was identified as a separate period (3) because of a specific interest for the Atlantic tropical cyclones that hit the Caribbean and the South-Eastern coast of the USA; phase 3 is also of interest in certain aspects of the aerosol export westwards over the Atlantic. While phases 0, 1 and 2 correspond to well defined regional climatic patterns their exact time frame obviously varies from year to year. Now, the heavy SOP deployment (aircraft and balloons) cannot cover continuously the entire year; thus only a limited part of each phase will be documented by the full SOP setup. These sub-periods are called SOP0, SOP1, SOP2 and SOP3 as shown in Figure 4. A number of different platforms and instruments will be deployed in these sub-periods, in different characteristic modes according to their needs and scientific outputs.

Some EOP ground-based networks will be enhanced regionally for a large part of the SOP year – for instance the GPS network and lidar networks will be enhanced in this period. At the same time new ground-based systems will be installed for the SOP year: as an example, the ARM Mobile Facility (AMF) is now installed at Niamey and will operate until 31 December 2006. Other ground-based systems will be installed for sub-periods, according to their scientific priorities (e.g. radars to target precipitation systems in the rainy months of SOP1 and SOP2).
Ships, balloons and aircraft, whose deployments are by necessity relatively short, will be coordinated with the ground-based deployments for specific parts of the SOPs, as illustrated in Fig. 5. Within a given SOP, specific aircraft campaigns are defined with a suffix ‘_a1’, ‘_a2’ or ‘_a3’, so that, for example, the second phase of aircraft activity in SOP2, at which we aim to deploy 5 research aircraft in cooperation, is denoted SOP2_a2. The detailed coordination of these instruments is given in the IIP.

SOP List of Instruments up

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