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Glossary and Acronyms: R

Radiosonde:

an expendable meteorological instrument package, often borne aloft by a free-flight balloon, that measures, from the surface to the stratosphere, the vertical profiles of atmospheric variables and transmits the data via radio to a ground receiving system. Radiosondes typically measure temperature, humidity, and, in many cases, pressure.

Regional Association (RA):

constituent body of the WMO (World Meteorological Organization), formed of WMO members situated in a large geographical region such as a continent, which controls the different meteorological regulations in that region. The six WMO Regions are Africa, RA I; Asia, RA II; South America, RA III; North and Central America, RA IV; South-West Pacific, RA V; and Europe, RA VI.
South-West Indian Ocean is part of the RA I Africa.

Ridge:

an elongated area of relatively high atmospheric pressure, almost always associated with and most clearly identified as an area of maximum anticyclonic curvature of wind flow. The locus of this maximum curvature is called the ridge line.

RMW:

Radius of maximum winds.

Rossby number:

Non-dimensional ratio (Ro) of the inertial force to the Coriolis force for a particular flow of rotating fluid, expressed as : Ro=U/fL, where U is a characteristic velocity ; f, the Coriolis parameter ; and L, a characteristic length. It gives the relative importance of the accelerations due to the centrifugal force and to the Coriolis force (deviating force) ; an approximate classification of the different types of flows is :

Rossby parameter:

Parameter β expressing the latitudinal variation of the Coriolis parameter f, arising from the sphericity of the Earth, expressed as: β = δf/ δy = (2 ω Cosθ)/a, where ω is the angular velocity of the Earth; θ, the latitude; and a, the Earth's radius.

Rossby radius of deformation:

the effective length of the lateral distance between the region of distubance generation and its outermost extent: LR=(gh)½ f, where f is the Coriolis parameter; g, the acceleration due to gravity; and h, the height.

Rossby régime:

type of flow pattern in a rotating fluid with differential radial heating in which the major radial transport of heat and momentum is effected by horizontal eddies of low wave-number, i.e. by very large eddies.

Rossby wave:

long wave, planetary wave. Wave in the atmospheric circulation, in one of the principal zones of the westerly winds, characterized by a great length and a significant amplitude.

RSMC:

Regional Specialized Meteorological Center. The Tropical Cyclone Centre Météo-France / La Réunion has been formally designated as the Regional Specialized Meteorological Centre - Tropical Cyclones for the South-West Indian Ocean by the World Meteorological Organization (WMO) in 1993.
The RSMC La Réunion is responsible for the monitoring of all the tropical systems occurring over its area of responsibility (from the equator to 40°S and between African coastline to 90°E). Its primary mission is to provide appropriate guidance information (analysis, forecasts) to the 15 countries, members of the region (Botswana, Comoros, France, Kenya, Lesotho, Madagascar, Malawi, Mauritius, Mozambique, Seychelles, South Africa, Swaziland, Tanzania, Zimbabwe).

RSS:

Remote Sensing Systems. A research company located in California, specialized in processing and analyzing microwave data collected by satellite microwave sensors.