35th Anniversary of first airborne Doppler radar measurements made in a tropical cyclone

Debby_LF_box
Composite horizontal reflectivity distribution in Debby for 1930-2014 UTC, 14 September 1982. The storm center is denoted by the hurricane symbol and the solid white line is the aircraft track. The dashed white line denotes the Doppler analysis domain shown below.

On September 14, 1982, while NOAA42 was flying the first Synoptic Flow experiment, NOAA43 was taking the first Doppler radar readings from an aircraft in a tropical cyclone. The flight into Hurricane Debby was designed to fly several legs into and out of the eye, forming triangular areas where the radar scans would overlap from different segments of the flight track (see figure above).  This allowed researchers to calculate (post-flight) the wind vectors within the overlap area.  Prior to this, the only wind measurements taken within tropical cyclones were just along the flight track of the aircraft.  Now the entire wind field of the core of a hurricane could be calculated from a single flight.

Detail of the track of flight 19820914I1 into Hurricane Debby

Using the Debby measurements, Frank Marks and Bob Houze (1984) described for the first time important asymmetric TC structure characteristics. Data from orthogonal flight legs from one aircraft were combined into a three-dimensional pseudo-dual-Doppler horizontal wind analysis assuming that features were stationary during the observation time (see figure below). This allowed for the first description of mesocyclones associated with potentially destructive local wind speed maxima superimposed on the basic flow.

Debby_Doppler1-3-5km
Doppler radar wind field wind fields at three different altitudes from Hurricane Debby [Marks and Houze (1984)] over a domain denoted in the radar image above. The red circle denotes a second circulation center displaced ~25 km WNW from the main storm circulation center (denoted by the hurricane symbol).
Prior to the 1982 Hurricane Field Program, the tail radar of the NOAA43 aircraft had been modified to take Doppler measurements.  Named for Christian Doppler, such radars read not only the strength of the return signal but also the shift in frequency of the return.  This shift is proportional to the speed of the target toward or away from the radar antenna.  If an area of precipitation is measured by two Doppler radars or by one Doppler radar from two locations (such as from a moving aircraft) then the vectors of the rain particles’ motions can be calculated.

References

Marks, F.D. Jr. and R.A. Houze Jr., “Airborne Doppler Radar Observations in Hurricane Debby” Bulletin of the American Meteorological Society, June 1984, Vol. 65, No. 6, pp.569-582