First Observations of Tracking Clouds Using Scanning ARM Cloud Radars

Trackingcloudsusingscanningcloud radars can helptodocument thetemporalevolution ofcloud properties wellbeforelarge-dropformation(weatherradar‘‘firstecho’’).Thesemeasurementsalsocomplementcloudand precipitation tracking using geostationary satellites and weather radars. Here, two-dimensional (2D) alongwind range‐height indicator observations of a population of shallow cumuli (with and without precipitation) from the 35-GHz scanning Atmospheric Radiation Measurement Program (ARM) cloud radar (SACR) at the U.S. Department of Energy (DOE)‐ARM Southern Great Plains (SGP) site are presented. Observations from theARMSGPnetworkofscanningprecipitationradarsareusedtoprovidethelarger-scalecontextofthecloud field and to highlight the advantages of the SACR to detect the numerous small nonprecipitating cloud elements. A new cloud identification and tracking algorithm (CITA) is developed to track cloud elements. In CITA, a cloud element is identified as a region having a contiguous set of pixels exceeding a preset reflectivity and size threshold. The high temporal resolution of the SACR 2D observations (30s) allows for an area superposition criteria algorithm to match cloud elements at consecutive times. Following CITA, the temporal evolution of cloud-element properties (number, size, and maximum reflectivity) is presented. The vast majority of the designated elements during this cumulus event were short-lived nonprecipitating clouds having an apparent life cycle shorter than 15min. The advantages and disadvantages of cloud tracking using an SACR are discussed.

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