1. Challenges associated with ice and large particles in the TTL
Terry Deshler
University of Wyoming, Laramie
Why do we care?
What is known?
The challenges
Seychelles 2010

2. Importance of aerosol in the TTL
Ice
Plays an essential role in controlling the humidity of air entering the stratosphere
Impacts radiative transfer at the TTL
Thus it is important to:
Characterize the frequency of ice particles in the TTL
Characterize the size distributions of ice to
Characteize fall speeds.
Estimate fraction of ice entering stratosphere
Estimate their radiative impact
Non-ice aerosol
Provide ice nuclei for subvisible cirrus
Population of particles for lifting into stratosphere with the large scale ascending circulation

3. 18 km
16.5
15 km
Lawson et al., acp, CRAVE

4. Lawson et al., acp, 2008

5. Davis et al. jgr, CRAVE

6. Davis et al.
jgr, 2010
Reverdy et al., acp, 2012

7. Jensen et al., pnas, 2013 – East Pacific

8. Challenges particle measurements
In situ
Size resolve particles from 0.1 – 100 µm
Concentrations from 10 – 1000 L-1 (0.01 – 1 cm-3)
Ice water content to 0.05 mg/m3
Instruments with size range µm have not been used on balloon-borne platforms.
Interesting region primarily below 18 km
Cannot determine cloud depth
Remote
Extinction range to 0.01 km-1
Optical depth to 0.01
Below range of CALIPSO
Cloud depth possible

9. Cirrus cloud just below the tropopause, Laramie, Wyoming

10. Altitude ~19.5 km, Pressure 62-66 hPa, Temperature -75 to -85 C
20 February 1 March March April April May May
Particle measurements completed during test campaign for Concordiasi. Flight duration 20 February – 10 May 2010
Altitude ~19.5 km, Pressure hPa, Temperature -75 to -85 C

11. Background aerosol size distributions

12. Background aerosol size distributions, with some large particles and maybe a cloud

13. Conclusions In situ particle measurements Remote measurements
Are not likely to have many opportunities to measure ice due to the altitude of the balloon platform
The size distribution of background aerosol is 0.05 – 1.0 um, for ice um
To complete such measurements requires typically 3 instruments on aircraft.
There is no single instrument which can cover this size range.
The concentrations for ice is within the capability of present instruments.
Remote measurements
More appropriate - will extend the satellite profiles to lower optical depth.
Can resolve cloud thickness and thus optical depth