ATTREX cloud measurements & implications for dehydration in the Tropical Tropopause Layer

B. Gandrud a, E. Jensen b, G. Diskin c, R. P. Lawson a, S. Lance a, S. Woods a, T. P. Bui b, R. Gao d and T. Thornberry d

-SPEC Inc, Boulder, CO a

-NASA Ames Research Center, Mountain View, CA b

-NASA Langley Research Center, Hampton, VA c

-NOAA Earth Systems Research Laboratory, Boulder, CO d

ATTREX2013 payload locations

Fast Cloud Droplet Probe (FCDP)

-count & size based on forward scattering-design to eliminate/reduce shattering-1 to 50 µ diameter with oversize bin-modern high speed electronics w/ pbp http://www.specinc.com/instrumentation

Supporting measurements

• NASA DLH (Diskin), open path WV• NOAA Water Vapor & Total Water

(Thornberry & Gao)• multiple WV measurements with emphasis on

quality• NASA MeteorologicalMeasurement System

(Bui)– T, P, winds, latitude & longitude

ATTREX2011 results• Jensen et al, PNAS 1217104110, p2041-2046, January 22,

2013• Homogeneous freezing responsible for high ice numbers in

thin layers• Heterogeneous freezing responsible for low ice numbers over

larger regions, above, below and in the absence of high ice concentration layers

• High ice concentration numbers effectively deplete water vapor in excess of saturation but this does not imply irreversible dehydration because the particles do not grow large enough to fall out

• Implication for models that moist air with SRice >1 can be transported across the TTL

20130205 flight SF01

-designed to sample cold air near SW end of flight path

-very thin cloud observed during 2nd vertical profile-single particle/second counts observed throughout flight, falling ??

-very thin cloud appears when SRice just exceeds 1

-descent and ascent very similar-particles in the largest bin & in oversize

20130205 size distributions

-high concentration cloud at S end of flight track

20130226 flight SF05

-particles form when SRi>1

-events with large number of particles remove water vapor from the parcel and drive SRi closer to 1

20130301 flight planning

-designed to sample cold pool in eastern Pacific

ATTREX 20130301 (R0 data)

TTL measurement in eastern Pacific

-9 cloud encounters

20130301 Cloud 3

-large cirrus concentration drives SRice down to near 1-large SRice observed with low cirrus concentration

20130301 Cloud9

-even cirrus concentration ~300 drives SRice to near 1-SRice >1 observed with low cirrus concentration

20130301 size distributions

100

101

102

10-3

10-2

10-1

100

101

Particle Size (um)

Con

cent

ratio

n (#

/L/u

m)

SF6 2013/03/01, Averaged FCDP Conc PSDs

Cloud 1Cloud 2Cloud 3Cloud 4Cloud 5Cloud 6Cloud 7Cloud 8Cloud 9

FCDP & TW comparison

20130301 Cloud4

- uncertainty in FCDP sizing and density of ice- uncertainties in TW enhancement factor

2013 results to date:-agreement with 2011 showing 2 categories of cirrus, high & low ice concentrations corresponding to homogeneous and heterogeneous freezing respectively

-5 of 6 flights show cirrus concentrations greater than 1000 L-1 in thin layers, usual size mode is under 10µ diameter

-all flights show cirrus concentrations in the 1-200 L-1 range over larger extent, usual size mode is over 10µ diameter

-comparison of water mass derived from FCDP and NOAA TW instrument are in reasonable agreement

Acknowledgements:

-SPEC Inc. grant funding from NASA Radiation Science Program-NASA Dryden Aircraft Operations Facility-Global Hawk ground and flight crews-ESPO at NASA Ames Research Center-and all of the science participants

NOAA TW enhancement factor