Environmental & Climate Sciences Department Seminar

The links of atmospheric vertical motions and the ice content within clouds are numerous. Vertical motions generate the supersaturation that allows ice nucleation; they determine whether mass transfer will occur from droplets to crystals by the Bergeron process; and they control the sedimentation rate from the cloudy layer to lower altitudes. I will present the ways in which we have tried to better understand this dynamic-microphysical relationship over the past few years. First, with an automatic differentiation-based attribution analysis, we see the importance of accurately representing updrafts for the number concentration of nucleated ice crystals on a global scale. Then we zoom in, using a parcel model to identify joint temperature-updraft regimes in which secondary ice production processes like rime splintering or frozen droplet shattering can significantly enhance ice content. Along with these direct connections via hydrometeor formation, the relationship of vertical velocity and cloud ice content affects surface precipitation. We illustrate this indirect hydrological impact with mesoscale simulation of a mid-latitude cold frontal rain band and satellite data analyses of cloud top phase and precipitation from mesoscale convective systems throughout the tropics.