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S. R. Pal and A. I. Carswell

Abstract

The effects of ice crystals on the backscatter polarization in lidar returns have been measured. Scattering from ground-level snow of varying density, high-altitude cirrus clouds and ice pellet shower clouds has been studied using a linearly polarized ruby laser system with multiple receiver channels. The space and time dependence of the total intensity and the linear depolarization ratio δ of the lidar return have been investigated. It has been found that considerable variations occur in snow with δ varying between 0.2 and 0.8. In cirrus and ice pellet shower clouds δ is typically found to lie in the range 0.3 ± 0.1. The factors involved in the use of polarization data for ice-water discrimination in the atmosphere are presented and discussed.

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A. I. Carswell, A. Fong, S. R. Pal, and I. Pribluda

Abstract

This paper summarizes the results of a statistical analysis of lidar-determined cloud geometrical properties measured during the 1989 and 1991 campaigns of the Experimental Cloud Lidar Pilot Study. Useful lidar descriptors are introduced to specify the bottom-, top-, and midcloud altitudes. These are used to describe the behavior of cloud vertical location and vertical extent during several months of observations using a dual wavelength (1064 and 532 nm) Nd:YAG lidar at Toronto. Frequency distributions of cloud height and cloud thickness are presented and the relationship of the lidar descriptors to cloud properties are discussed. These data are compared with other information on cloud geometry available in the literature.

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S. R. Pal, A. I. Carswell, I. Gordon, and A. Fong

Abstract

This paper presents the Statistical properties of lidar-derived values of cloud extinction coefficients σ and optical depths τ. The data were collected at Toronto during two measurement phases (phase 1: September–October 1989; phase 2: June–July 1991) or the Experimental Cloud Lidar Pilot Study. Although the small dataset limits general application of the statistical trends observed, the measurements demonstrate the valuable potential of lidar data for improving cloud parameterization in general circulation models. The measurements show the frequent occurrence of optically thin clouds (σ¯≤0.2 km−1 and τ≤0.2), demonstrating the ability of lidars to detect these dilute clouds and the importance of including them in radiative transfer models.

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C. M. Platt, S. A. Young, A. I. Carswell, S. R. Pal, M. P. McCormick, D. M. Winker, M. DelGuasta, L. Stefanutti, W. L. Eberhard, M. Hardesty, P. H. Flamant, R. Valentin, B. Forgan, G. G. Gimmestad, H. Jäger, S. S. Khmelevtsov, I. Kolev, B. Kaprieolev, Da-ren Lu, K. Sassen, V. S. Shamanaev, O. Uchino, Y. Mizuno, U. Wandinger, C. Weitkamp, A. Ansmann, and C. Wooldridge

The Experimental Cloud Lidar Pilot Study (ECLIPS) was initiated to obtain statistics on cloud-base height, extinction, optical depth, cloud brokenness, and surface fluxes. Two observational phases have taken place, in October–December 1989 and April–July 1991, with intensive 30-day periods being selected within the two time intervals. Data are being archived at NASA Langley Research Center and, once there, are readily available to the international scientific community.

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H. J. S. Fernando, E. R. Pardyjak, S. Di Sabatino, F. K. Chow, S. F. J. De Wekker, S. W. Hoch, J. Hacker, J. C. Pace, T. Pratt, Z. Pu, W. J. Steenburgh, C. D. Whiteman, Y. Wang, D. Zajic, B. Balsley, R. Dimitrova, G. D. Emmitt, C. W. Higgins, J. C. R. Hunt, J. C. Knievel, D. Lawrence, Y. Liu, D. F. Nadeau, E. Kit, B. W. Blomquist, P. Conry, R. S. Coppersmith, E. Creegan, M. Felton, A. Grachev, N. Gunawardena, C. Hang, C. M. Hocut, G. Huynh, M. E. Jeglum, D. Jensen, V. Kulandaivelu, M. Lehner, L. S. Leo, D. Liberzon, J. D. Massey, K. McEnerney, S. Pal, T. Price, M. Sghiatti, Z. Silver, M. Thompson, H. Zhang, and T. Zsedrovits

Abstract

Emerging application areas such as air pollution in megacities, wind energy, urban security, and operation of unmanned aerial vehicles have intensified scientific and societal interest in mountain meteorology. To address scientific needs and help improve the prediction of mountain weather, the U.S. Department of Defense has funded a research effort—the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program—that draws the expertise of a multidisciplinary, multi-institutional, and multinational group of researchers. The program has four principal thrusts, encompassing modeling, experimental, technology, and parameterization components, directed at diagnosing model deficiencies and critical knowledge gaps, conducting experimental studies, and developing tools for model improvements. The access to the Granite Mountain Atmospheric Sciences Testbed of the U.S. Army Dugway Proving Ground, as well as to a suite of conventional and novel high-end airborne and surface measurement platforms, has provided an unprecedented opportunity to investigate phenomena of time scales from a few seconds to a few days, covering spatial extents of tens of kilometers down to millimeters. This article provides an overview of the MATERHORN and a glimpse at its initial findings. Orographic forcing creates a multitude of time-dependent submesoscale phenomena that contribute to the variability of mountain weather at mesoscale. The nexus of predictions by mesoscale model ensembles and observations are described, identifying opportunities for further improvements in mountain weather forecasting.

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