severe weather, defense, marine, public weather and  environmental monitoring. The information is down linked  either via Very High Frequency (VHF) communications  through the Aircraft Communications Addressing and  Reporting System (ACARS) or via satellite link through the  Aircraft to Satellite Data Acquisition and Relay (ASDAR).  The Meteorological Data Collection and Reporting System  (MDCRS) is an automated airborne weather observation  program that is used in the U.S. This program collects and  disseminates real-time upper-air weather observations from  participating airlines. The weather elements are down linked  via ACARS and are managed by Aeronautical Radio, Inc.  (ARINC) who then forwards them in Binary Universal Form  for the Representation of Meteorological Data (BUFR)  format to the NWS and in raw data form to the Earth Science  Research Laboratory (ESRL) and the participating airline.  More than 1,500 aircraft report wind and temperature data  with some of these same aircraft also providing turbulence  and humidity/water vapor information. In conjunction with  avionics manufacturers, each participating airline programs  their equipment to provide certain levels of meteorological  data. The monitoring and collection of climb, en route, and  descent data is accomplished through the aircraft’s Flight Data  Acquisition and Monitoring System (FDAMS) and is then  transmitted via ACARS. When aircraft are out of ACARS  range, reports can be relayed through ASDAR. However, in  most cases, the reports are buffered until the aircraft comes  within ACARS range, at which point they are downloaded.  There are four types of radars which provide information  about precipitation and wind.  Precipitation targets provide stronger return signals;  therefore, the radar is operated in the Precipitation  mode when precipitation is present. A faster antenna  rotation in this mode allows images to update at  a faster rate, approximately every 4 to 6 minutes.  Intensity values in both modes are measured in  dBZ (decibels of Z) and are depicted in color on the  radar image.  [Figure 13-1]  Intensities are correlated  to intensity terminology (phraseology) for ATC  purposes.  [Figures 13-2  and  13-3]  Figure 13-2.  WSR-88D Weather Radar Echo Intensity Legend.  Figure 13-3.  WSR-88D Weather Radar Precipitation Intensity  Terminology.  Radar Observations  1. The WSR-88D NEXRAD radar, commonly called  Doppler radar, provides in-depth observations that  inform surrounding communities of impending  weather. Doppler radar has two operational modes:  clear air and precipitation. In clear air mode, the radar  is in its most sensitive operational mode because a  slow antenna rotation allows the radar to sample the  atmosphere longer. Images are updated about every  10 minutes in this mode.  Figure 13-1.  Example of a weather radar scope.  Weather Radar Echo Intensity  Light  Moderate  Heavy  Extreme  Reflectivity (dBZ) Ranges  <30 dBZ  30–40 dBZ  >40–50  50+ dBZ  13-3 