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

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

18 km 16.5 15 km Lawson et al., acp, 2008 - CRAVE

Lawson et al., acp, 2008

Davis et al. jgr, 2010 - CRAVE

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

Jensen et al., pnas, 2013 – East Pacific

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 0.002 to 0.05 mg/m3 Instruments with size range 30 -100 µm have not been used on balloon-borne platforms. Interesting region primarily below 18 km Cannot determine cloud depth Remote Extinction range 0.005 to 0.01 km-1 Optical depth 0.0005 to 0.01 Below range of CALIPSO Cloud depth possible

Cirrus cloud just below the tropopause, Laramie, Wyoming

Altitude ~19.5 km, Pressure 62-66 hPa, Temperature -75 to -85 C 20 February 1 March 15 March 1 April 15 April 1 May 10 May Particle measurements completed during test campaign for Concordiasi. Flight duration 20 February – 10 May 2010 Altitude ~19.5 km, Pressure 62-66 hPa, Temperature -75 to -85 C

Background aerosol size distributions

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

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 1-100 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