Microphysical and radiative properties of tropical clouds investigated in TC4 and NAMMA

Abstract

[1] The size, shape and concentration of ice particles in tropical anvil cirrus and in situ cirrus clouds have a significant impact on cloud radiative forcing, and hence on global climate change. Data collected in tropical anvil and cirrus clouds with a 2D-S probe, an optical imaging probe with improved response characteristics and the ability to remove shattered artifacts, are analyzed and discussed. The data were collected with NASA DC-8 and WB-57F research aircraft near Costa , ice water contents exceeding 2 g m −3 and total particle concentrations exceeding 10 cmat 12.2 km. Ice water contents in the anvils declined outward from the center of convection, decreasing to <0.1 g m −3 in aged anvil cirrus. The data show that microphysical and radiative properties of both tropical anvils and cirrus are most strongly influenced by ice particles in the size range from about 100 to 400 mm. This is contrary to several previous investigations that have suggested that ice particles less than about 50 mm control radiative properties in anvils and cirrus. The 2D-S particle area and mass size distributions, plus information on particle shape, are input into an optical properties routine that computes cloud extinction, asymmetry parameter and single scattering albedo. These optical properties are then input into two-stream radiative code to compute radiative heating profiles within the various cloud types. The results produce short-and long-wave heating/cooling vertical profiles in these tropical clouds. A simple parameterization based on 2D-S measurements is derived from the particle mass size distribution that yields an area size distribution. The parameterized area size distribution can then be used in large-scale numerical simulations that include radiative transfer packages.

Dimensions and aspect ratios of natural ice crystals

“…The average D (µm) of crystals (columns; plates; bullets) in non-anvil clouds (154.0; 122.3; 132.6) are larger than those in anvil clouds (109.8; 104.0; 99.9) during TWP-ICE, whereas those in anvil clouds (187.2; 117.5; 158.5) are larger than those in non-anvil clouds (158.1; 116.3; 132.8) during SPARTICUS at −67 < T < −35 • C. shows a strong dependence on the type of cirrus, and is much higher in anvil clouds compared to non-anvil clouds for TWP-ICE and SPARTICUS, which agrees with previous studies (e.g., Connolly et al, 2005;Um and McFarquhar, 2009;Lawson et al, 2010). In general, crystal dimensions are found to increase with temperature (e.g., Fig.…”

“…16). This is consistent with bulk ice sizes increasing with temperature as observed in situ (e.g., Lawson et al, 2010) and from satellite measurements (e.g., Yuan and Li, 2010;van Diedenhoven et al, 2014b). Furthermore, the general weak dependence of crystal aspect ratio on temperature shown in Fig.…”

On Polarimetric Radar Signatures of Deep Convection for Model Evaluation: Columns of Specific Differential Phase Observed during MC3E*

“…The microphysical properties of mature deep convection updrafts remain poorly quantified, at least in part because of sparse in situ measurements available from aircraft campaigns, which provide the only direct means of measuring hydrometeor mixing ratio, morphology, size distribution, and phase within strong updrafts Stith et al 2002Stith et al , 2004Anderson et al 2005;Stith et al 2006;Lawson et al 2010). A glaring result is the lack of observational data adequate to quantitatively constrain order-of-magnitude differences in condensate mixing ratios commonly predicted by cloud-resolving simulations of deep convection systems using differing microphysics schemes, where interaction of dynamics and microphysics schemes likely contribute to differences (Varble et al 2011;Zhu et al 2012;Collis et al 2013;.…”

A statistical comparison of cirrus particle size distributions measured using the 2-D stereo probe during the TC&lt;sup&gt;4&lt;/sup&gt;, SPARTICUS, and MACPEX flight campaigns with historical cirrus datasets

“…Mitchell et al (2011) demonstrated that, for a given effective diameter and IWC, the optical properties of a PSD are sensitive to its shape. Therefore, PSD bimodality and concentrations of small ice crystals are critical to realistically parameterizing cirrus PSDs, to modeling their radiative properties and sedimentation velocities, and to mathematical forward models designed to infer cirrus PSDs from remote-sensing observations (Lawson et al, 2010;Mitchell et al, 2011;Lawson, 2011). In order to improve knowledge on PSD shape, as well as to develop statistical algorithms for correcting historical PSD datasets so that PSD shapes are corrected along with computations of bulk properties, it will be necessary to make use of instruments that can provide reliable measurements of small ice crystals beneath the size floors of both the 2DC and the 2D-S.…”

“…The opposite is true for the 2DC. This is attributed to the 2D-S's larger sample volume; to its improvements in resolution and electronic time response over the 2DC; and to its 256 photodiode elements (Jensen et al, 2009;Lawson, 2011;Brenguier et al, 2013), which allow it to size particles smaller than 100 µm and to measure particle inter-arrival times more accurately (Lawson et al, 2010;Korolev et al, 2013b;Brenguier et al, 2013).…”