The First ISCCP Regional Experiments have been designed to improve data products and cloud/radiation parameterizations used in general circulation models (GCMs). Specifically, the goals of FIRE are (1) to improve basic understanding of the interaction of physical processes in determining life cycles of cirrus and marine stratocumulus systems and the radiative properties of these clouds during their life cycles and (2) to investigate the interrelationships between the ISCCP data, GCM parameterizations, and higher space and time resolution cloud data.To-date, four intensive field-observation periods were planned and executed: a cirrus IFO (October 13-November 2, 1986); a marine stratocumulus IFO off the southwestern coast of California (June 29-July 20, 1987); a second cirrus IFO in southeastern Kansas (November 13-December 7, 1991); and a second marine stratocumulus IFO in the eastern North Atlantic Ocean (June 1-June 28, 1992). Each mission combined coordinated satellite, airborne, and surface observations with modeling studies to investigate the cloud properties and physical processes of the cloud systems. The University of North Dakota owns and operates a Cessna Citation II aircraft (N77ND) for the purpose of atmospheric research. This aircraft type has a number of design and performance characteristics which make it an ideal platform for a wide range of atmospheric studies. A series of structural modifications have been made to the basic airplane. These include the following: pylons under the wing tips for a variety of probes in the undisturbed air flow away from the fuselage; a nose boom for wind measurement; a heated radome to prevent ice accumulation on the nose area; special mounts for upward and downward looking radiometers; side-facing camera mounts for time-lapse cameras; optically-flat glass windows for photography; and an air inlet port for air sampling inside the pressurized cabin. The research instrumentation available on the Citation for the second Cirrus IFO is described below.The basic instrumentation package measured temperature, dew point temperature, pressure, wind and cloud microphysical characteristic along with aircraft position, altitude and performance parameters. The three-dimensional wind field is derived from measurements of acceleration, pitch, roll and yaw combined with angles of attack and sideslip and indicated airspeed. The aircraft parameters were supplied by an LTN-76 inertial navigation system and a Global Positioning System (GPS). Turbulence intensity can be derived from differential pressure transducers and INS accelerometer outputs. Cloud microphysical measurements were made with an array of Particle Measuring Systems probes (FSSP, 1D-C,2D-C,1D-P) mounted on the wing-tip pylons. These probes measure concentrations and sizes of particles from one micrometer to several millimeters in diameter. In addition there were probes to measure both liquid water content and icing rate. Several gas and aerosol sampling instruments were available. These include fast response O3 and NO2 monitors, and a condensation nuclei counter. A forward or side-looking video camera was also used to provide a visual record of flight conditions. The data were sampled at various rate from 1 to 24 sec-1. The sampling is controlled by the on-board computer system which also displayed the data in real time in graphic and alphanumeric formats while recording them on magnetic tape.