The structure and mesoscale organization of precipitating stratocumulus Export

@article{SavicJovcicStevens2007Drizzle, abstract = {Large-eddy simulations are used to explore the structure and mesoscale organi- zation of precipitating stratocumulus. The simulations incorporate a simple, two- moment, bulk representation of microphysical processes, which by varying specified droplet concentrations allows for comparisons of simulations that do and do not de- velop precipitation. The boundary layer is represented over a large (25.6 by 25.6 km) horizontal domain using a relatively fine mesh, thereby allowing for the development of mesoscale circulations while retaining an explicit representation of cloud radiative, dynamical and microphysical interactions on scales much smaller than the dominant eddy scale. Initial conditions are based on measurements made as part of the sec- ond dynamics and chemistry of marine stratocumulus field study (DYCOMS-II). The simulations show that precipitation is accompanied by sharp reductions in cloudiness and changes in flow topology. Mesoscale features emerge in all of the simulations, but are amplified in the presence of drizzle. A cloud albedo of near 75\% in the non- precipitating simulation is reduced to less than 35\% in the precipitating case. The circulation transitions from a well mixed, stationary stratocumulus layer with closed- cellular cloud planforms to a stationary cumulus-coupled layer, with incipient open- cellular cloud planforms and sustained domain-averaged surface precipitation rates near 1 mm day−1 . The drizzling simulations embody many other features of observed precipitating stratocumulus, including elevated cloud tops in regions of precipitation and locally higher values of sub-cloud equivalent potential temperature. The latter is shown to result from the tendency for precipitating simulations to develop greater ther- modynamic gradients in the sub-cloud layer as well as mesoscale circulations which locate regions of upward motion in the vicinity of precipitating cells.}, author = {Savic-Jovcic, Verica and Stevens, Bjorn}, citeulike-article-id = {1602570}, journal = {Journal of Atmospheric Sciences}, keywords = {clouds-low, drizzle, les}, posted-at = {2007-08-29 02:47:04}, priority = {0}, title = {The structure and mesoscale organization of precipitating stratocumulus}, volume = {in press}, year = {2007} }

TY - JOUR ID - SavicJovcicStevens2007Drizzle L3 - citeulike-article-id:1602570 N2 - Large-eddy simulations are used to explore the structure and mesoscale organi- zation of precipitating stratocumulus. The simulations incorporate a simple, two- moment, bulk representation of microphysical processes, which by varying specified droplet concentrations allows for comparisons of simulations that do and do not de- velop precipitation. The boundary layer is represented over a large (25.6 by 25.6 km) horizontal domain using a relatively fine mesh, thereby allowing for the development of mesoscale circulations while retaining an explicit representation of cloud radiative, dynamical and microphysical interactions on scales much smaller than the dominant eddy scale. Initial conditions are based on measurements made as part of the sec- ond dynamics and chemistry of marine stratocumulus field study (DYCOMS-II). The simulations show that precipitation is accompanied by sharp reductions in cloudiness and changes in flow topology. Mesoscale features emerge in all of the simulations, but are amplified in the presence of drizzle. A cloud albedo of near 75% in the non- precipitating simulation is reduced to less than 35% in the precipitating case. The circulation transitions from a well mixed, stationary stratocumulus layer with closed- cellular cloud planforms to a stationary cumulus-coupled layer, with incipient open- cellular cloud planforms and sustained domain-averaged surface precipitation rates near 1 mm day−1 . The drizzling simulations embody many other features of observed precipitating stratocumulus, including elevated cloud tops in regions of precipitation and locally higher values of sub-cloud equivalent potential temperature. The latter is shown to result from the tendency for precipitating simulations to develop greater ther- modynamic gradients in the sub-cloud layer as well as mesoscale circulations which locate regions of upward motion in the vicinity of precipitating cells. JF - Journal of Atmospheric Sciences TI - The structure and mesoscale organization of precipitating stratocumulus VL - in press KW - clouds-low KW - drizzle KW - les AU - Savic-Jovcic, Verica AU - Stevens, Bjorn PY - 2007/// ER -