IN Ice Nuclei Nice Ice Number Concentration GCM Global Climate Model GCSS WG2 GEWEX Cloud System Study Working Group 2 GEWEX Global Energy and Cycle Experiment FSSP Forward Scattering Spectrometer Probe α Deposition Coefficient RHi Relative humidity respect to ice MAID Model for Aerosol and Dynamic GW Gravity Wave N-Mass Nucleation mode aerosol size spectrometer FCAS-II Focused cavity aerosol spectrometer MTP Microwave temperature profiler PALMS Particle Analysis by Mass Spectrometry LRT1 First Lapse Rate LRT2 Second Lapse Rate Tg Glassy temperature S Entropy H Enthalpy DSC Differential Scanning Calorimeter Cp Isobaric Heat Capacity PCS2000 Optical Particle Spectrometer FTIR Infrared Extinction Spectrometer PSC Polar Stratospheric Clouds
which does not cover the whole range of observed ice number density (0.005-0.2 cm-3) (see Fig 5.19). Figure 5.19 model result of ice number density and relative humidity versus time. The cirrus model is forced with the balloon observed temperature fluctuations with IN concentration of 0.005 cm-3. Summary and conclusion In this chapter, we have shown the effect of single and multiple gravity waves on cirrus clouds through investigations using the Advanced Particle Simulation Code cirrus model. We progressively moved to more complex and realistic gravity wave simulations resulting in the work in which we use balloon observations of temperature fluctuations taken from months of balloon observations of TTL conditions. Our model results using these gravity wave forcings show many results but most importantly we show that the commonly observed TTL cirrus properties are consistent with gravity wave forcings only when glassy nucleation is present. This suggests that glassy or a similar common and abundant aerosol nucleator must be present to explain observations. I now present the more specific results of the chapter: Single gravity waves with different amplitude and time periods of 20-100 cm/sec and 90s respectively have been implemented in our cirrus model for both homogeneous and heterogeneous runs. The freezing threshold and cloud properties are determined by the amplitude and frequency of gravity waves. Forming cirrus cloud along the homogeneous pathway needs higher wave amplitude and lower wave frequency than cloud formed on glassy aerosol particles.
0.5 K/day to 6 K/ day. By increasing the uplift speed, more ice water content and ice crystals form with smaller sizes due to the fact that higher super-saturations are reached before the ice particles can quench excess humidity. Higher super-saturations lead to high ice fractions activated. Figure 6.9: The heating rates (in output time interval 130 or time=325 min) with height in modeled cirrus cloud formed on glassy aerosol particles for different vertical velocities, other conditions are as the same as Figure 6.2. Radiation simulations have been performed with different solar zenith angles to test the impact of solar zenith angle on cloud radiative heating vertical profiles during the day. The solar zenith angle is expected to have a significant effect on the solar radiative properties since this is what some satellite instruments take advantage of to see very thin cirrus clouds that are sub-visible if viewed directly overhead with the sun also overhead. The satellites (such as MODIS) use the fact that these thin clouds can have significant optical paths if the sun is at a grazing angle and can pick up the presence of cirrus for this situation. However, these clouds will still have small radiative properties because the clouds are so thin. So, the radiative heating rate of sub-visible cloud is not expected to be significant even though it may change a lot with different solar zenith angles. Figure 6.10 shows that changing the solar zenith angle factor in the model from 5°, 30°, 60°, and 85° leads to the following cloud solar heating rates of 0.43, 0.68, 0.83 and 0.86 K/day, respectively, and roughly an increase of an order of 0.1 K/day in infra-red heating rate. The IR heating rate is increased because the increased solar heating rate in the layer increases the temperature in the atmosphere and this alters the IR radiative properties which are very