Campaign : Small Particles in Cirrus (SPartICus)

1 October 2009-30 September 2010

Lead Scientist : Gerald Mace

Scientific Focus

Because clouds in the upper troposphere exert a significant influence on the radiative balance of the earth system, our understanding of the processes that control their occurrence and properties is fundamental to eventual improvements of their correct representation in global climate models (GCMs). The radiative effects of upper tropospheric clouds (hereafter referred to as cirrus) stem from both their microphysical and macrophysical properties. The particles composing cirrus extend over a broad range of sizes with particles whose sizes are 10s of microns controlling the total number of crystals in a volume while particles whose sizes range from hundreds of microns to in excess of a millimeter being most prominent in the distribution of condensed mass (McFarquhar and Heymsfield 1996, 1997, Heymsfield et al. 1998). The radiative influence of cirrus then stem from these microphysical properties with reflection of solar radiation causing a net cooling of the climate system (Ackerman et al., 1988). That cirrus are strong absorbers in the thermal IR and that they exist at cold upper tropospheric temperatures ensure that they exert a substantial warming influence in the thermal IR (Stephens et al., 1990). There exists a delicate balance between cooling and heating by cirrus that is modulated by the macroscale properties of cirrus layers such as their physical thickness and overall spatial coverage and cloud layer lifetime (Mace et al., 2006; 2007; Mather et al., 2007).

Relevancy to ARM

Our present understanding of cirrus and the physical controls on their properties stem from both remote sensing measurements like that traditionally provided by ARMs ground based ACRF and from in situ measurements collected by aircraft (Mace et al., 2002; Deng and Mace, 2006; Zhang and Mace 2007). Because ground based remote sensing provides limited information, cloud property retrieval algorithms applied to ground-based data rely heavily on empirical information from in situ data such as the relationships between the cross sectional area or mass and cirrus particle maximum dimension (i.e. Mitchell, 1996; Heymsfield et al., 2002; Baker and Lawson 2006). Without reasonably precise information regarding these empirical relationships, ARMs ground-based retrieval algorithms suffer both bias and random errors that are presently unknown in magnitude but can be as large as a factor of 2 or more (Comstock et al., 2007). Without a substantial improvement in our overall data base of in situ data there is little hope of improving these results. Furthermore, characterizations of cloud property retrieval errors are fundamental since the foundational goal of ARM is to characterize cloud properties. Without correlative measurements from which a statistically significant comparison between ground-based retrievals and in situ measurements is possible, we are unable to characterize retrieval errors and are therefore unable to meet ARM goals in anything more than a qualitative fashion. We contend that the present state of affairs is unacceptable, and we will propose an airborne mission to be conducted by jet aircraft over the SGP ACRF with state of the art probes to address the outstanding science and measurement issues.

Description of Proposed Campaign

It has been our experience conducting airborne cirrus measurement campaigns over ground-based instruments in the mid latitudes that typically between 1 and 3 significant events can be captured during a typical month. This is why previous field programs have provided at most a few case studies per deployment hardly sufficient to address many of our science questions. Our goal with SPartICus is to create a data set that rigorously addresses outstanding science and measurement questions in a statistically significant fashion. To accomplish this, we will propose to conduct reasonably routine in situ measurements over the SGP ACRF. We anticipate attempting at most 1-2 flights per week depending on meteorolgoical and instrument conditions. Ideally, these flights will occur after sundown so that we can take advantage of optimal observing conditions for the Raman Lidar. The flights will be of 2-3 hours duration and will need to extend to altitudes of 14 km. Typical meteorological conditions in which the flights will take place will be benign since we will require the cirrus to be visible from the ground by the Raman Lidar, and we have no great interest in flying close to thunderstorms.

Critical instrumentation at the SGP ACRF will include the routine measurements provided by the MMCR, the Raman lidar, and the AERI. Other routine ACRF measurements will also be used but are considered ancillary. No special radiosonde launches will be need for the routine flight of SPartICus.

The instrument suite on the aircraft will include measurements of the particle size distribution with special emphasis on small particles, condensed mass, optical extinction, particle habit, humidity, temperature, pressure in addition to the normal aircraft state parameters. We require redundancy on the critical measurements and in order to compare the behavior of several instruments. The instruments that are best suited for SPartICus are still being studied and will be described in the full proposal.

Flight patterns will be straightforward. Spirals up and down through the cirrus layer immediately downwind of the Raman Lidar and MMCR radar profiles will be the primary measurement approach. We anticipate using pre-defined flight patterns and flight times so that routine observations of representative cirrus conditions can be emphasized

ARM Resources Needed to Support Campaign

See above.

Additional Information

We have initiated discussions with NASA (Hal Maring) regarding a possible leveraging of resources for this mission. NASA has a strong interest in characterizing the measurement issues discussed above.

The dates listed above are placeholders. We recognize that this campaign will be costly and that both the time period and the number of flights may be limited by available resources. We are aware that the campaign will need to be scaled to meet available resources. However, we are convinced that many science questions could be addressed with limited resources.

References:

Ackerman, T. P., K. N. Liou, F. P. J. Valero, L. Pfister, 1988: Heating rates in tropical anvils. J. Atmos. Sci., 45, 1606-1624. Baker, B. and R. P. Lawson, 2006: Improvement in determination of ice water content from two-dimesional particle imager. Part I: Image-to-mass relationships. J. Applied Meteorol. Climatology, 45, 1282-1291. Comstock, J. M, R. d'Entremont, D. DeSlover, G. G. Mace, S. Y. Matrosov, S. McFarlane, P. Minnis, D. Mitchell, K. Sassen, M Shupe, D. Turner, Z. Wange, 2007: An intercomparison of microphysical retrieval algorithms for upper tropospheric ice clouds. Beuaru of the American Meteorological Society. In Press. Deng, M. and G. Mace, 2006: Cirus microphysical properties and air motion statistics using cloud radar Doppler moments: Part I Algorithm description. J. Applied Meteorology and Climatology, 45, 1690-1709.

Heymsfield, AJ, S. Lewis, A. B. Bansemer, J. Iaquinta, L. M. Miloshevich, M. Kajikawa, C. Twohy, M. R. Poellot, (2002), A General Approach for Deriving the Properties of Cirrus and Stratiform Ice Cloud Particles. J. Atmos. Sciences., 59, 3-29 Heymsfield A. J., G. M. Mcfarquhar, W. D. Collins, J. A. Goldstein, F. P. J., Valero, J. Spinhirne, W. Hart, P. Pilewskie, 1998: Cloud properties leading to highly reflective tropical cirrus: interpretations from CEPEX, TOGA COARE, and Kwajalein, Marshall Islands . J. of Geophys. Research, 103, 8805-8812. 1998.

Jensen, E. J., D. Baumgardner, G. McFarquhar, S. Platnick, G. T. Arnold, Evaluation of the Plausibility of In Situ Measurements in Anvil Cirrus Clouds Indicating Ubiquitous Small Ice Crystals, manuscript in preparation.

Kristjansson, JE, and J. M. Edwards, and D. Mitchell, 1999: A new parameterization scheme for the optical properties of ice crystals for use in general circulation models of the atmosphere. Physics and Chemistry of the Earth. B: Hydrology, Oceans and Atmosphere, 24, 231-236.

Mace, G. G., and S. Benson, 2007: The vertical distribution of cloud radiative forcing at the SGP ARM Climate Research Facility as revealed by 8-years of continuous data. Submitted to Journal of Climate. Mace, G. G., S. Benson, and S. Kato, 2006: Cloud Radiative Forcing at the ARM Climate Research Facility: Part 2. The vertical redistribution of radiant energy by clouds. J. Geophys. Res., 111, D11S91, doi:10.1029/2005JD005922. Mace G. G A. J. Heymsfield, M. R. Poellot, 2002: On retrieving the microphysical properties of cirrus using millimeter wave Doppler moments data, J. Geophys. Res. 107, DOI 10.1029/2001JD001308 Mather, J. H., S. A. McFarlane, M. A. Miller, K. L. Johnson, 2007: Cloud properties and associated radiative heating rates in the tropical western pacific. J. Geophys. Res., 112, doi: 10.1029/2006JD007555. McFarquhar, G. M., J. Um, M. Freer, D. Baumgardner, G L. Kok, and G. G. Mace, 2007: The importance of small ice crystals to cirrus properties: Observations from the Tropical Warm Pool International Cloud Experiment (TWP-ICE). Submitted to Geophys. Res. Letters.

McFarquhar, G. M., P. Yang, A. Macke, and A. J. Baran 2002: A New Parameterization of Single Scattering Solar Radiative Properties for Tropical Anvils Using Observed Ice Crystal Size and Shape Distributions. J. Atmos. Sci., 59, 2458-2478. McFarquhar, G. M., and A. J. Heymsfield, 1997: Parameterization of tropical cirrus ice size distributions and implications for radiative transfer: results from CEPEX . J. Atmos. Sciences, 54, 2187-2200. McFarquhar, G. M., and A. J. Heymsfield, 1996: Microphysical characteristics of three anvils sampled during the Central Equatorial Pacific Experiment. J. Atmos. Sciences, 53, 2401-2423

Stephens, G. L., S.-C. Tsay, J. P. W. Stackhouse, and P. J. Flatau, 1990: the relevance of the microphysical and radiative properties of cirrus clouds to climate and climatic feedback. J. Atmos. Sci., 47, 1742-1753. Zhang, Y., and G. Mace, 2006: Retrieval of cirrus microphysical properties with a suite of algorithms for airborne and spaceborne lidar, radar and radiometer data. J. Applied Meteorology and Climatology, 45, 1665-1708.