Discrete Topographic and Orographic Clouds of Mars

Abstract This article is a review of work on the subject of seedability of winter orographic clouds for increasing precipitation. Various aspects of seedability are examined in the review, including definitions, distribution of supercooled liquid water, related meteorological factors, relationship of supercooled liquid water to storm stage, factors governing seedability, and the use of seeding criteria. Of particular interest is the conclusion that seedability is greatest when supercooled liquid water concentrations are large and at the same time precipitation rates are small. Such a combination of conditions is favored if the cloud-top temperature is warmer than a limiting value and as the cross-barrier wind speed at mountaintop levels increases. It is also suggested that cloud seeding is best initiated in accordance with direct measurements of supercooled liquid water, precipitation, and cross-barrier wind speed. However, in forecasting these conditions or in continuation of seeding previously initiated, the cloud-top temperature and cross-barrier wind speed are the most useful quantities.

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Dual-Polarization Radar Data Analysis of the Impact of Ground-Based Glaciogenic Seeding on Winter Orographic Clouds. Part I: Mostly Stratiform Clouds

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-14-0257.1 ◽

2015 ◽

Vol 54 (9) ◽

pp. 1944-1969 ◽

Cited By ~ 12

Author(s):

Xiaoqin Jing ◽

Bart Geerts ◽

Katja Friedrich ◽

Binod Pokharel

Keyword(s):

Radar Data ◽

Control Area ◽

Target Area ◽

Dual Polarization ◽

Stratiform Clouds ◽

Orographic Clouds ◽

Close Range ◽

Glaciogenic Seeding ◽

Differential Reflectivity ◽

The Impact

AbstractThe impact of ground-based glaciogenic seeding on wintertime orographic, mostly stratiform clouds is analyzed by means of data from an X-band dual-polarization radar, the Doppler-on-Wheels (DOW) radar, positioned on a mountain pass. This study focuses on six intensive observation periods (IOPs) during the 2012 AgI Seeding Cloud Impact Investigation (ASCII) project in Wyoming. In all six storms, the bulk upstream Froude number below mountaintop exceeded 1 (suggesting unblocked flow), the clouds were relatively shallow (with bases below freezing), some liquid water was present, and orographic flow conditions were mostly steady. To examine the silver iodide (AgI) seeding effect, three study areas are defined (a control area, a target area upwind of the crest, and a lee target area), and comparisons are made between measurements from a treated period and those from an untreated period. Changes in reflectivity and differential reflectivity observed by the DOW at low levels during seeding are consistent with enhanced snow growth, by vapor diffusion and/or aggregation, for a case study and for the composite analysis of all six IOPs, especially at close range upwind of the mountain crest. These low-level changes may have been affected by natural changes aloft, however, as evident from differences in the evolution of the echo-top height in the control and target areas. Even though precipitation in the target region is strongly correlated with that in the control region, the authors cannot definitively attribute the change to seeding because there is a lack of knowledge about natural variability, nor can the outcome be generalized, because the sample size is small.

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Optical properties of continental haze and cumulus and orographic clouds based on Space Shuttle polarimetric observations

Applied Optics ◽

10.1364/ao.32.006841 ◽

1993 ◽

Vol 32 (33) ◽

pp. 6841 ◽

Cited By ~ 6

Author(s):

Walter G. Egan ◽

S. Israel ◽

M. Sidran ◽

E. E. Hindman ◽

W. R. Johnson ◽

...

Keyword(s):

Optical Properties ◽

Space Shuttle ◽

Orographic Clouds

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Effects of Cloud Condensation Nuclei and Ice Nucleating Particles on Precipitation Processes and Supercooled Liquid in Mixed-phase Orographic Clouds

10.5194/acp-2016-772 ◽

2016 ◽

Cited By ~ 1

Author(s):

Jiwen Fan ◽

L. Ruby Leung ◽

Daniel Rosenfeld ◽

Paul J. DeMott

Keyword(s):

Water Content ◽

Sierra Nevada ◽

Cloud Condensation Nuclei ◽

Supercooled Water ◽

Mixed Phase ◽

Condensation Nuclei ◽

Local Circulation ◽

Orographic Clouds ◽

Snow Precipitation ◽

Mixed Phase Clouds

Abstract. How orographic mixed-phase clouds respond to the change of cloud condensation nuclei (CCN) and ice nucleating particles (INPs) are highly uncertain. The main snow production mechanism in warm and cold mixed-phase orographic clouds (referred to as WMOC and CMOC, respectively, distinguished here as those having cloud tops warmer and colder than −20 °C) could be very different. We quantify the CCN and INP impacts on supercooled water content, cloud phases and precipitation for a WMOC and a CMOC case with a set of sensitivity tests. It is found that deposition plays a more important role than riming for forming snow in the CMOC, while the role of riming is dominant in the WMOC case. As expected, adding CCN suppresses precipitation especially in WMOC and low INP. However, this reverses strongly for CCN > 1000 cm−3. We find a new mechanism through which CCN can invigorate mixed-phase clouds over the Sierra Nevada Mountains and drastically intensify snow precipitation when CCN concentrations are high (1000 cm−3 or higher). In this situation, more widespread shallow clouds with greater amount of cloud water form in the valley and foothills, which changes the local circulation through more latent heat release that transports more moisture to the windward slope, leading to much more invigorated mixed-phase clouds over the mountains that produce higher amounts of snow precipitation. Increasing INPs leads to decreased riming and mixed-phase fraction in the CMOC but has the opposite effects in the WMOC, as a result of liquid-limited and ice-limited conditions, respectively. However, it increases precipitation in both cases due to an increase of deposition for the CMOC but enhanced riming and deposition in the WMOC. Increasing INPs dramatically reduces supercooled water content and increases the cloud glaciation temperature, while increasing CCN has the opposite effects with much smaller significance.

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Orographic clouds in north Victoria Land from AVHRR images

Polar Record ◽

10.1017/s003224740006753x ◽

1996 ◽

Vol 32 (183) ◽

pp. 317-324 ◽

Cited By ~ 6

Author(s):

Giuseppe Zibordi ◽

Massimo Frezzotti

Keyword(s):

High Resolution ◽

Satellite Imagery ◽

Meteorological Data ◽

Spectral Features ◽

Katabatic Winds ◽

Victoria Land ◽

Avhrr Data ◽

Orographic Clouds ◽

Temporal Occurrence ◽

Very High

ABSTRACTOrographic clouds over north Victoria Land, East Antarctica, have been observed in Advanced Very High Resolution Radiometer (AVHRR) satellite imagery. These occasional clouds are discussed through analysis of their spectral features in AVHRR data. Temporal occurrence, spatial extension, and direction of the clouds are also discussed in relation to meteorological data for two periods characterised by katabatic winds, in December 1992 and January 1993.

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Single particle analysis of ice crystal residuals observed in orographic wave clouds over Scandinavia during INTACC experiment

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-1977-2006 ◽

2006 ◽

Vol 6 (7) ◽

pp. 1977-1990 ◽

Cited By ~ 61

Author(s):

A. C. Targino ◽

R. Krejci ◽

K. J. Noone ◽

P. Glantz

Keyword(s):

Elemental Composition ◽

Organic Material ◽

Mineral Dust ◽

Hierarchical Cluster ◽

Sea Salt ◽

Particle Analysis ◽

Crystal Formation ◽

Strong Impact ◽

Ice Crystal ◽

Orographic Clouds

Abstract. Individual ice crystal residual particles collected over Scandinavia during the INTACC (INTeraction of Aerosol and Cold Clouds) experiment in October 1999 were analyzed by Scanning Electron Microscopy (SEM) equipped with Energy-Dispersive X-ray Analysis (EDX). Samples were collected onboard the British Met Office Hercules C-130 aircraft using a Counterflow Virtual Impactor (CVI). This study is based on six samples collected in orographic clouds. The main aim of this study is to characterize cloud residual elemental composition in conditions affected by different airmasses. In total 609 particles larger than 0.1 μm diameter were analyzed and their elemental composition and morphology were determined. Thereafter a hierarchical cluster analysis was performed on the signal detected with SEM-EDX in order to identify the major particle classes and their abundance. A cluster containing mineral dust, represented by aluminosilicates, Fe-rich and Si-rich particles, was the dominating class of particles, accounting for about 57.5% of the particles analyzed, followed by low-Z particles, 23.3% (presumably organic material) and sea salt (6.7%). Sulfur was detected often across all groups, indicating ageing and in-cloud processing of particles. A detailed inspection of samples individually unveiled a relationship between ice crystal residual composition and airmass origin. Cloud residual samples from clean airmasses (that is, trajectories confined to the Atlantic and Arctic Oceans and/or with source altitude in the free troposphere) were dominated primarily by low-Z and sea salt particles, while continentally-influenced airmasses (with trajectories that originated or traveled over continental areas and with source altitude in the continental boundary layer) contained mainly mineral dust residuals. Comparison of residual composition for similar cloud ambient temperatures around –27°C revealed that supercooled clouds are more likely to persist in conditions where low-Z particles represent significant part of the analyzed cloud residual particles. This indicates that organic material may be poor ice nuclei, in contrast to polluted cases when ice crystal formation was observed at the same environmental conditions and when the cloud residual composition was dominated by mineral dust. The presented results suggest that the chemical composition of cloud nuclei and airmass origin have a strong impact on the ice formation through heterogeneous nucleation in supercooled clouds.

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