Andrew Heymsfield

General Information

MMM - TIIMES
Senior Scientist
UTLS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: FL3 - 3035
Telephone: 303-497-8943
Email: heyms1@ucar.edu
Home Page - Vita

Research Focus FY08:

I led the Ice in Clouds-Layer Experiment (ICE-L) in November and December, 2007 and was the scientist onboard the C130 for sixty of the seventy research and test flight hours. In that capacity, I organized and ran the daily planning meetings and directed the C130 to locations and clouds amenable to wave clouds. We had thirteen research flights and six of them are exceptionally valuable for studying ice formation processes and quantifying ice nuclei and ice crystal concentrations. We worked closely with modelers who used WRF and to model probable wave cloud locations, heights and vertical motion fields. The combination of the upward-looking lidar and the upward and downward looking cloud Doppler radar provide an unprecedented view of ice formation locations and streamlines. We had eight different probe measuring droplets, drops, and small ice.

I continue to uncover major errors in earlier observations from instruments that measure or sense ice particle size distributions. I developed analytic relationships--a set of four equations--to quantify the shattering signal. From these relations, I can duplicate many earlier observations of particle size distributions in ice clouds. More importantly, these relations allow me to subtract out the shattering component to find where small ice particles actually are occurring. I can now identify regions of homogeneous ice nucleation and mixed-phase cloud. I submitted an article to {Geophys. Res. Ltrs.}, reporting on this work. The article was published in December.

I extended this work to the workhorse of particle probes, the 2D-C. The 2D-C sizes particle  from about 50 microns to several mm. More than a half-dozen articles have shown from spiral descent through ice clouds that the slopes of snow size distributions decrease to a value of about 9 per cm and then remaining there. Several theoretical arguments have been proposed to explain this finding. In the article I submitted, I show that the result is an artifact due to ice shattering on the 2D-C's leading edge.

I assembled a group of investigators to describe the current state of knowledge of the microphysical processes and properties of contrails, how they morph into contrail cirrus, the long-term effects of aviation-produced carbon aerosols, and how contrail microphysics is represented in climate models. The study also suggested what can be done in the next several years to improve the representation of contrails in climate models and what is still needed but currently unavailable to reduce the current uncertainty in the radiative impacts of contrails.

I received funding this year from NASA for a three-year effort to improve the representation of ice microphysics in climate models. As part of this effort, I found an interesting feature in CloudSat observations. The hope is that CloudSat will be able to derive snow precipitation rates in region of cloud above the melting layer from radar reflectivity. What I found was that CloudSat (94 GHz) cannot reliably determine these rates because of an interesting feature that is related to Mie scattering. The larger particles in the first 1 km or so above the melting layer actually reduce the reflectivity below the values measure above them because of their interference of the radar signal because the particle size is comparable or larger than the radar wavelength. This feature can produce a factor of up to four underestimate in the precipitation rate. I studied the process from a theoretical standpoint and developed theoretical/analytic methods to correct for it.

Community Service FY08:

• Editor: Journal of Atmospheric Sciences
• CloudSat Science Team, NASA
• Graduate Advisor: Carl Schmitt, University of Colorado
• Graduate Advisor: Aaron Pratt, Howard Univeristy, Washington D.C.
• Graduate Advisor: Udaya Bhaskar, Massachusetts Institute of Technology, Boston, MA
• Graduate Advisor: Norm Wood, Colorado State University, Fort Collins, CO
• Thesis Committee: Matt Shupe, University of Colorado
• Thesis Committee: Sean Davis, University of Colorado

Scientific Talks FY08:

• Ice formation in clouds at temperatures from -10 to -30C (Cancun, Mexico, July 2008)
• Ice Cloud Properies (Leeds, UK, June 2008)
• Aerosols and Clouds (Utrecht, Netherlands, April 2008)
• The ICE-L field program: measurements and results (Manchester, UK, June 2008)
• Ice Formation thru heterogeneous nucleation (Vienna, Austria, April 2008)
• Contrail microphysics (Virginia Beach, VA February 2008)
• In-situ/radar observations from TC4 (Virginia Beach, VA February 2008)
• Ice Cloud Properties (Stockholm, Sweden, September 2008)

Publications FY08 (abstracts):

Twohy, C., S. M. Kreidenweis, T. Eidhammer, E. V. Browell, A. J. Heymsfield, A. Bansemer, B. E. Anderson, G. Chen, S. Ismail, P. J. Demott, S. C. Van Den Heever, 2008: Saharan dust particles nucleate droplets in eastern Atlantic clouds. Geophys. Res. Lett.. (Submitted)

Heymsfield, A. J., P. Field, A. Bansemer, 2008: Explaining the lower limit to slopes of ice particle size distributions. J. Atmos. Sci.. (In Press)

Hong, G., P. Yang, B. A. Baum, A. J. Heymsfield, F. Weng, Q. Liu, 2008: Scattering database in the millimeter and submillimeter wave range of 100-1000 GHz for nonspherical ice crystals. J. Geophys. Res.. (In Press)

Matrosov, S. Y., A. J. Heymsfield, 2008: Estimating ice content and extinction in precipitating cloud systems from CloudSat radar measurements. J. Geophys. Res., 113, D00A05, doi: 10.1029/2007JD009633.

Skofronick-Jackson, G., A. J. Heymsfield, E. Holthaus, C. Albers, M.-J. Kim, 2008: Correction to "Nonspherical and spherical characterization of ice in Hurricane Erin for wideband passive microwave comparisons". J. Geophys. Res., 113, D14210, doi: 10.1029/2008JD010387.

Halverson, J., M. Black, S. Braun, D. Cecil, M. Goodman, A. J. Heymsfield, G. Heymsfield, R. Hood, T. Krishnamurti, G. McFarquhar, M. J. Mahoney, J. Molinari, R. Rogers, J. Turk, C. Velden, D.-L. Zhang, E. Zipser, R. Kahar, 2008: NASA's tropical cloud systems and processes (TCSP) experiment: Investigating tropical cyclogenesis and hurricane intensity change. Bull. Amer. Meteor. Soc., 88, 867-882, doi: 10.1175/BAMS-88-6-867.

Jenkins, G. S., A. S. Pratt, A. J. Heymsfield, 2008: Possible linkages between Saharan dust and tropical cyclone rain band invigoration in the eastern Atlantic during NAMMA-06. Geophys. Res. Lett., 35, L08815, doi: 10.1029/2008GL034072.

Field, P. R., A. J. Heymsfield, A. Bansemer, C. H. Twohy, 2008: Determination of the combined ventilation factor and capacitance for ice crystal aggregates from airborne observations in a tropical anvil cloud. J. Atmos. Sci., 65, 376-391, doi: 10.1175/2007JAS2391.1.

Skofronick-Jackson, G., A. J. Heymsfield, E. Holthaus, C. Albers, M.-J. Kim, 2008: Nonspherical and spherical characterization of ice in Hurricane Erin for wideband passive microwave comparisons. J. Geophys. Res., 113, D06201, doi: 10.1029/2007JD008866.

Heymsfield, A. J., A. Bansemer, S. Matrosov, L. Tian, 2008: The 94-GHz radar dim band: Relevance to ice cloud properties and cloudsat. Geophys. Res. Lett., 35, L03802, doi: 10.1029/2007GL03136.

Heymsfield, A. J., A. Protat, D. Bouniol, R. T. Austin, R. J. Hogan, J. Delanoe, H. Okamoto, K. Sato, G.-J. vanZadelhoff, D. P. Donovan, Z. Wang, 2008: Testing IWC retrieval methods using radar and ancillary measurements with in-situ data. J. Appl. Meteor. Climat., 47, 135-163, doi: 10.1175/2007JAMC1606.1.

Schmitt, C. G., A. J. Heymsfield, 2007: On the occurrence of hollow bullet rosette- and column-shaped ice crystals in midlatitude cirrus. J. Atmos. Sci., 64, 4514-4519, doi: 10.1175/2007JAS2317.1.

Field, P. R., A. J. Heymsfield, A. Bansemer, 2007: Snow size distribution parameterization for midlatitude and tropical ice clouds. J. Atmos. Sci., 64, 4346-4365, doi: 10.1175/2007JAs2344.1testing.

Heymsfield, A. J., 2007: On measurements of small ice particles in clouds. Geophys. Res. Lett., 34, L23812, doi: 10.1029/2007GL030951.

McFarquhar, G. M., G. Zhang, M. R. Poellot, G. L. Kok, R. McCoy, T. Tooman, A. Fridlind, A. J. Heymsfield, 2007: Ice properties of single-layer stratocumulus during the Mixed-Phase Arctic Cloud Experiment: 1 Observations. J. Geophys. Res., 112, D24201, doi: 10.1029/2007JD008633.

Fridlind, A. M., A. S. Ackerman, G. M. McFarquhar, G. Zhang, M. R. Poellot, P. J. DeMott, A. J. Prenni, A. J. Heymsfield, 2007: Ice properties of single-layer stratocumulus during the Mixed-Phase Arctic Cloud Experiment: 2 Model results. J. Geophys. Res., 112, D24202, doi: 10.1029/2007JD008646.

Delanoe, J., A. Protat, D. Bouniol, A. J. Heymsfield, A. Bansemer, P. Brown, 2007: The characterization of ice cloud properties from Doppler radar measurements. J. Appl. Meteor. Climat., 46, 1682-1698, doi: 10.1175/JAM2543.1.