Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 2 2009 10.5194/acpd-9-5321-2009 http://www.atmos-chem-phys-discuss.net/9/5321/2009/ http://www.atmos-chem-phys-discuss.net/9/5321/2009/acpd-9-5321-2009.html http://www.atmos-chem-phys-discuss.net/9/5321/2009/acpd-9-5321-2009.pdf 5321 5370 2009-03-02 On the importance of small ice crystals in tropical anvil cirrus E. J. Jensen eric.j.jensen@nasa.gov P. Lawson B. Baker B. Pilson Q. Mo A. J. Heymsfield A. Bansemer T.P. Bui M. McGill D. Hlavka G. Heymsfield S. Platnick G. T. Arnold S. Tanelli NASA Ames Research Center, Moffett Field, CA, USA SPEC Inc., Boulder, CO, USA National Center for Atmospheric Research, Boulder, CO, USA NASA Goddard Space Flight Center, Greenbelt, MD, USA Jet Propulsion Laboratory, Pasadena, CA, USA In situ measurements of ice crystal concentrations and sizes made with aircraft instrumentation over the past two decades have often indicated the presence of numerous relatively small (<50 μm diameter) crystals in cirrus clouds. Further, these measurements frequently indicate that small crystals account for a large fraction of the extinction in cirrus clouds. The fact that the instruments used to make these measurements, such as the Forward Scattering Spectrometer Probe (FSSP) and the Cloud Aerosol Spectrometer (CAS), ingest ice crystals into the sample volume through inlets has led to suspicion that the indications of numerous small-crystals could be artifacts of large-crystal shattering on the instrument inlets. We present new aircraft measurements in anvil cirrus sampled during the Tropical Composition, Cloud, and Climate Coupling (TC4) campaign with the 2-Dimensional Stereo (2D-S) probe, which detects particles as small as 10 μm. The 2D-S has detector "arms" instead of an inlet tube, and therefore is expected to be less susceptible to shattering artifacts than instruments such as CAS. In addition, particle inter-arrival times are used to identify and remove shattering artifacts that occur even with the 2D-S probe. The number of shattering artifacts identified by the 2D-S interarrival time analysis ranges from a negligible contribution to an order of magnitude or more enhancement in apparent ice concentration over the natural ice concentration, depending on the abundance of large crystals and the natural small-crystal concentration. The 2D-S measurements in tropical anvil cirrus suggest that natural small-crystal concentrations are typically one to two orders of magnitude lower than those inferred from CAS. The strong correlation between the CAS/2D-S ratio of small-crystal concentrations and large-crystal concentration suggests that the discrepancy is likely caused by shattering of large crystals on the CAS inlet. We argue that past measurements with CAS in cirrus with large crystals present may contain errors due to crystal shattering, and past conclusions derived from these measurements may need to be revisited. Further, we present correlations between CAS spurious concentration and 2D-S large-crystal mass from spatially uniform anvil cirrus sampling periods as an approximate guide for estimating quantitative impact of large-crystal shattering on CAS concentrations in previous datasets. We use radiative transfer calculations to demonstrate that in the maritime anvil cirrus sampled during TC4, small crystals indicated by 2D-S contribute relatively little to cloud extinction, radiative forcing, or radiative heating in the anvils, regardless of anvil age or vertical location in the clouds. While 2D-S ice concentrations in fresh anvil cirrus may often exceed 1 cm−3, and are observed to exceed 10 cm−3 in turrets, they are typically ~0.1 cm−3 and rarely exceed 1 cm−3 (<1.4% of the time) in aged anvil cirrus. It appears that the numerous small crystals detrained from convective updrafts do not persist in the anvil cirrus sampled during TC-4. We hypothesize that isolated occurrences of higher ice concentrations in aged anvil cirrus are caused by ice nucleation driven by gravity waves. Baker, B., Mo, Q., Lawson, R P., Korolev, A., and O'Connor, D.: Drop size distributions and the lack of small drops in RICO rain shafts, J. Atmos. Sci., 1, in press, 2009. Baumgardner, D., Jonsson, H., Dawson, W., Connor, D O., and Newton, R.: The cloud, aerosol and precipitation spectrometer (CAPS): A new instrument for cloud investigations, Atmos. Res., 59, 59–60, 2001. Baumgardner, D., Chepfer, H., Raga, G B., and Kok, G L.: The shapes of very small cirrus particles derived from in situ measurements, Geophys. Res. Lett., 32, L01806, doi:10.1029/2004GL021300, 2005. Chepfer, H., Noel, V., Minnis, P., Baumgardner, D., Nguyen, L., Raga, G., McGill, M J., and Yang, P.: Particle habit in tropical ice clouds during CRYSTAL-FACE: Comparison with two remote sensing techniques and with in situ observations, J. Geophys. Res., 110, D16204, doi:10.1029/2004JD005455, 2005. Cotton, R J. and Field, P R.: Ice nucleation characteristics of an isolated wave cloud, Q. J. Roy. Meteorol. Soc., 128, 2417–2437, doi:10.1256/qj.01.150, 2002. Cziczo, D J., Murphy, D M., Hudson, P K., and Thomson, D S.: Single particle measurements of the chemical composition of cirrus ice residue during CRYSTAL-FACE, J. Geophys. Res., 109, D04201, doi:10.1029/2003JD004032, 2004. Field, P R., Wood, R., Brown, P. R A., Kaye, P H., Hirst, E., and Greeaway, R.: Ice particle interarrival times measured with a fast FSSP, J. Atmos. Ocean. Tech., 20, 249–261, 2003. Field, P R., Heymsfield, A J., and Bansemer, A.: A test of ice self-collection kernels using aircraft data, J. Atmos. Sci., 63, 651–666, 2006. Fridlind, A M., Ackerman, A S., Jensen, E J., Heymsfield, A J., Poellot, M R., Stevens, D E., Wang, D., Miloshevich, L M., Baumgardner, D., Lawson, R P., Wilson, J C., Flagan, R C., Seinfeld, J H., Jonsson, H H., VanReken, T M., Varutbangkul, V., and Rissman, T A.: Evidence for the predominance of mid-tropospheric aerosols as subtropical anvil nuclei, Science, 303, 718–722, 2004. Fridlind, A M., Ackerman, A S., McFarquhar, G., Zhang, G., Poellot, M R., DeMott, P J., Prenni, A J., and Heymsfield, A J.: 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, 2007. Gardiner, B A. and Hallett, J.: Degradation of in-cloud Forward Scattering Spectrometer Probe measurements in the presence of ice crystals, J. Atmos. Ocean. Tech., 2, 171–180, 1985. Garrett, T J., Gerber, H., Baumgardner, D G., Twohy, C H., and Weinstock, E M.: Small, highly reflective ice crystals in low-latitude cirrus, Geophys. Res. Lett., 30, 2132, doi:10.1029/2003GL018153, 2003. Garrett, T J., Navarro, B C., Twohy, C H., Jensen, E J., Baumgardner, D G., Bui, P T., Gerber, H., Herman, R L., heymsfield, A J., Lawson, P., Minnis, P., Nguyen, L., Poellot, M., Pope, S K., Valero, F. P J., and Weinstock, E M.: Evolution of a Florida Cirrus Anvil, J. Atmos. Sci., 62, 2352–2372, 2005. Gayet, J.-F., Febvre, G., and Larsen, H.: The reliability of the PMS FSSP in the presence of small ice crystals, J. Atmos. Ocean. Tech., 13, 1300–1310, 1996. Gayet, J.-F., Auriol, F., Minikin, A., Ström, J., Seifert, M., Krejci, R., Petzold, A., Febvre, G., and Schumann, U.: Quantitative measurement of the microphysical and optical properties of cirrus clouds with four different insitu probes: Evidence of small ice crystals, Geophys. Res. Lett., 29, 2230, doi:10.1029/2001GL014342, 2002. Heymsfield, A J.: On measurements of small ice particles in clouds, Geophys. Res. Lett., 34, L23812, doi:10.1029/2007GL030951, 2007. Heymsfield, A J. and McFarquhar, G M.: On the high albedos of anvil cirrus in the tropical Pacific warm pool: Microphysical interpretations from CEPEX and Kwajalein, Marshall Islands, J. Atmos. Sci., 53, 2424–2451, 1996. Heymsfield, A J. and Miloshevich, L M.: Relative humidity and temperature influences on cirrus formation and evolution: Observations from wave clouds and FIRE II, J. Atmos. Sci., 52, 4302–4326, 1995. Hong, G., Yang, P., Gao, B.-C., Baum, B A., Hu, Y X., King, M D., and Platnick, S.: High cloud properties from three years of MODIS Terra and Aqua collection-4 data over the tropics, J. Appl. Meteorol. Clim., 46, 1840–1856, 2007. Hoyle, C R., Luo, B P., and Peter, T.: The origin of high ice crystal number densities in cirrus clouds, J. Atmos. Sci., 62, 2568–2579, 2005. Ivanova, D., Mitchell, D L., Arnott, W P., and Poellot, M.: A GCM parameterization for bimodal size spectra and ice mass removal rates in mid-latitude cirrus clouds, Atmos. Res., 59, 89–113, 2001. Jensen, E J. and Ackerman, A S.: Homogeneous aerosol freezing in the tops of high-altitude tropical cumulonimbus clouds, Geophys. Res. Lett., 33, L08802, doi:10.1029/2005GL024928, 2006. Jensen, E J., Kinne, S., and Toon, O B.: Tropical cirrus cloud radiative forcing: Sensitivity studies, Geophys. Res. Lett., 21, 2023–2026, 1994. Jensen, E J., Toon, O B., Tabazadeh, A., Sachse, G W., Anderson, B E., Chan, K R., Baumgardner, D., Twohy, C., Gandrud, B., Heymsfield, A., Aulenbach, S., Hallett, J., and Gary, B L.: Ice nucleation processes in upper tropospheric wave-clouds observed during SUCCESS, Geophys. Res. Lett., 25, 1363–1366, 1998. Jensen, E J., Pfister, L., Ackerman, A S., and Tabazadeh, A.: A conceptual model of the dehydration of air due to freeze-drying by optically thin, laminar cirrus rising slowly across the tropical tropopause, J. Geophys. Res., 106, 17273–17252, 2001. Kärcher, B. and Ström, J.: The roles of dynamical variability and aerosols in cirrus cloud formation, Atmos. Chem. Phys., 3, 823–838, 2003. Knollenberg, R G., Kelly, K., and Wilson, J C.: Measurements of high number densities of ice crystals in the tops of tropical cumulonimbus, J. Geophys. Res., 98, 8639–8664, 1993. Korolev, A. and Isaac, G A.: Shattering during sampling by OAPs and HVPS. Part I: Snow particles, J. Atmos. Ocean. Tech., 22, 528–542, 2005. Krämer, M., Schiller, C., Afchine, A., Bauer, R., Gensch, I., Mangold, A., Schlicht, S., Spelten, N., Sitnikov, N., Borrmann, S., de Reus, M., and Spichtinger, P.: Ice supersaturations and cirrus cloud crystal numbers, Atmos. Chem. Phys. Discuss., 8, 21089–21128, 2008. Lawson, R P., Baker, B A., Pilson, B., and Mo, Q.: In Situ observations of the microphysical properties of wave, cirrus and anvil clouds. Part II: Cirrus clouds, J. Atmos. Sci., 63, 3186–3203, 2006a. Lawson, R P., O'Connor, D., Zmarzly, P., Weaver, K., Baker, B A., Mo, Q., and Jonsson, H.: The 2D-S (Stereo) probe: Design and preliminary tests of a new airborne, high-speed, high-resolution imaging probe, J. Atmos. Ocean. Tech., 23, 1462–1477, 2006b. Lawson, R. P., Pilson, B., Baker, B., Mo, Q., Jensen, E., Pfister, L., and Bui, P.: Aircraft measurements of microphysical properties of subvisible cirrus in the tropical tropopause layer, Atmos. Chem. Phys., 8, 1609–1620, 2008. Magee, N., Moyle, A M., and Lamb, D.: Experimental determination of the deposition coefficient of small cirrus-like ice crystals near −50°C, Geophys. Res. Lett., 33, L17813, doi:10.1029/2006GL026665, 2006. McFarquhar, G M. and Heymsfield, A J.: Parameterization of tropical cirrus ice crystal size distributions and implications for radiative transfer: results from CEPEX, J. Atmos. Sci., 54, 2187–2200, 1997. McFarquhar, G M., Um, J., Freer, M., Baumgardner, D., Kok, G L., and Mace, G.: The importance of small ice crystals to cirrus properties: Observations from the Tropical Warm Pool International cloud Experiment (TWP-ICE), Geophys. Res. Lett., 57, L13803, doi:10.1029/2007GL029865, 2007. Miloshevich, L M. and Heymsfield, A J.: A balloon-borne continuous cloud particle replicator for measuring vertical profiles of cloud microphysical properties: Instrument design, performance, and collection efficiency analysis, J. Atmos. Ocean. Tech., 14, 753–768, 1997. Mitchell, D L., Rasch, P., Ivanova, D., McFarquhar, G., and Nousianen, T.: The impact of small ice crystal assumptions on sedimentation rates and GCM simulations, Geophys. Res. Lett., 35, L09806, doi:10.1029/2008GL033552, 2008. Platt, C. M R., Spinhirne, J D., and Hart, W D.: Optical and microphysical properties of a cold cirrus cloud: Evidence for regions of small ice particles, J. Geophys. Res., 41, 11151–11164, 1989. Sanderson, B M., Piani, C., Ingram, W J., Stone, D A., and Allen, M R.: Towards constraining climate sensitivity by linear analysis of feedback patterns in thousands of perturbed-physics GCM simulations, Clim. Dynam., 30, 175–190, doi:10.1007/s00382-007-0280-7, 2008. Sinha, A. and Shine, K P.: A one-dimensional study of possible cirrus cloud feedbacks, J. Climate, 7, 158–173, 1994. Stackhouse, P. W J. and Stephens, G L.: A theoretical and observational study of the radiative properties of cirrus: Results from FIRE 1986, J. Atmos. Sci., 48, 2044–2059, 1991. Ström, J., Strauss, B., Anderson, T., Schröder, F., Heintzenberg, J., and Wendling, P.: In situ observations of the microphysical properties of young cirrus clouds, J. Atmos. Sci., 54, 2542–2553, 1997. Toon, O B., McKay, C P., Ackerman, T P., and Santhaman, K.: Rapid calculation of radiative heating and photodissociation rates in inhomogeneous multiple scattering atmospheres, J. Geophys. Res., 94, 16287–16301, 1989. Twohy, C. H. and Poellot, M. R.: Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation, Atmos. Chem. Phys., 5, 2289–2297, 2005. Zender, C S. and Kiehl, J T.: Radiative sensitivities of tropical anvils to small ice crystals, J. Geophys. Res., 99, 25869–25880, 1994.