New Cloud Science from the New ARM Cloud Radar Systems (Invited)

The DOE ARM Program is deploying over $30M worth of scanning polarimetric Doppler radars at its four fixed and two mobile sites, with the object of advancing cloud lifecycle science, and cloud-aerosol-precipitation interaction science, by a quantum leap. As of 2011, there will be 13 scanning radar systems to complement its existing array of profiling cloud radars: C-band for precipitation, X-band for drizzle and precipitation, and two-frequency radars for cloud droplets and drizzle. This will make ARM the world’s largest science user of, and largest provider of data from, ground-based cloud radars. The philosophy behind this leap is actually quite simple, to wit: dimensionality really does matter. Just as 2D turbulence is fundamentally different from 3D turbulence, so observing clouds only at zenith provides a dimensionally starved, and sometimes misleading, picture of real clouds. In particular, the zenith view can say little or nothing about cloud lifecycle and the second indirect effect, nor about aerosol-precipitation interactions. It is not even particularly good at retrieving the cloud fraction (no matter how that slippery quantity is defined). This talk will review the history that led to this development and then discuss the aspirations for how this will propel cloud-aerosol-precipitation science forward. The step by step plan for translating raw radar data into information that is useful to cloud and aerosol scientists and climate modelers will be laid out, with examples from ARM’s recent scanning cloud radar deployments in the Azores and Oklahoma . In the end, the new systems should allow cloud systems to be understood as 4D coherent entities rather than dimensionally crippled 2D or 3D entities such as observed by satellites and zenith-pointing radars.