Figure 5. Profiles of horizontally averaged ice water content for four different ice crystal types. The warm stable case is shown in the left two columns, and the cold stable case is shown in the right two columns (adopted from Liu et al., 2003b).

the cold cirrus cases at 30° N. In addition, we assume that the surface albedo is 0.2, approximating a climatological average. The input parameters for the simulation sets are summarized in Table 3 of Liu et al. (2003b).

3.3. Results and discussions on the effect of ice crystal habit on the development of cirrus

Four types of ice crystal are considered here: columns, plates, bullet rosettes and spheres. The first three types are commonly observed in cirrus clouds, while the last one is a simplified approximation to ice particles. To focus on the effect of habit, we will consider only the development of cirrus in cold and warm stable atmospheres, but with the aggregation process turned off because of its insignificance in the stable environment. The results for the cases of cirrus in warm and cold unstable atmospheres are similar, but with different magnitudes. They will not be summarized here.

The sensitivity of cirrus development to ice crystal habit can be seen in Fig. 5 for warm and cold cirrus. For the warm stable cases, the peak amplitudes of the ice water content all occur around 40min, but their values are strongly habit-dependent. The maximum ice water content for cirrus consisting of rosettes is more than twice as large as for spheres. These maxima are similar for columns and plates, and are larger than for spheres but smaller than for rosettes. The results for the cold stable case are similar except that the ice water content reaches its maximum value around 90 min.

The corresponding profiles of mean crystal size for the warm and cold stable cases are shown in Fig. 6. Rosettes are largest, followed by plates and columns, while spheres are smallest. The difference in mean size between rosettes and spheres is as large as fourfold.

0 0

Post a comment