Mixed Phase and Ice Crystal Icing Envelope (Deep Convective Clouds)

The ice crystal icing envelope is depicted in Figure D1 of this Appendix.

Graphic printed in Appendix D to Part 33

Within the envelope, total water content (TWC) in g/m 3 has been determined based upon the adiabatic lapse defined by the convective rise of 90% relative humidity air from sea level to higher altitudes and scaled by a factor of 0.65 to a standard cloud length of 17.4 nautical miles. Figure D2 of this Appendix displays TWC for this distance over a range of ambient temperature within the boundaries of the ice crystal envelope specified in Figure D1 of this Appendix.

Ice crystal size median mass dimension (MMD) range is 50-200 microns (equivalent spherical size) based upon measurements near convective storm cores.

The TWC can be treated as completely glaciated (ice crystal) except as noted in the Table 1 of this Appendix.

Table 1—Supercooled Liquid Portion of TWC

Temperature range—deg C	Horizontal cloud length—nautical miles	LWC— g/m³
0 to −20	≤50	≤1.0
0 to −20	Indefinite	≤0.5
< −20		0

The TWC levels displayed in Figure D2 of this Appendix represent TWC values for a standard exposure distance (horizontal cloud length) of 17.4 nautical miles that must be adjusted with length of icing exposure.