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The origin of the broad emission line region (BELR) in quasars and activegalactic nuclei is still unclear. I propose that condensations form in thewarm, radiation pressure driven, accretion disk wind of quasars creating theBEL clouds and uniting them with the other two manifestations of cool, 10,000K, gas in quasars, the low ionization phase of the warm absorbers (WAs) and theclouds causing X-ray eclipses. The cool clouds will condense quickly (days toyears), before the WA outflows reach escape velocity (which takes months tocenturies). Cool clouds form in equilibrium with the warm phase of the windbecause the rapidly varying X-ray quasar continuum changes the forcemultiplier, causing pressure waves to move gas into stable locations inpressure-temperature space. The narrow range of 2-phase equilibrium densitiesmay explain the scaling of the BELR size with the square root of luminosity,while the scaling of cloud formation timescales could produce the Baldwineffect. These dense clouds have force multipliers of order unity and so cannotbe accelerated to escape velocity. They fall back on a dynamical timescale(months to centuries), producing an inflow that rains down toward the centralblack hole. As they soon move at Mach ~40 with respect to the WA outflow, these'raindrops' will be rapidly destroyed within months. This rain of clouds mayproduce the elliptical BELR orbits implied by velocity resolved reverberationmapping in some objects, and can explain the opening angle and destructiontimescale of the narrow 'cometary' tails of the clouds seen in X-ray eclipseobservations. Some consequences and challenges of this 'quasar rain' model arepresented along with several avenues for theoretical investigation.

Quasar Rain: the Broad Emission Line Region as Condensations in the Warm Accretion Disk Wind