Evaluation of temperature‐dependent complex refractive indices of supercooled liquid water using downwelling radiance and in‐situ cloud measurements at South Pole

2021 ◽  
Author(s):  
Penny M. Rowe ◽  
Von P. Walden ◽  
Richard E. Brandt ◽  
Michael S. Town ◽  
Stephen R. Hudson ◽  
...  
Keyword(s):  
Liquid Water ◽  
Supercooled Liquid ◽  
Refractive Indices ◽  
South Pole ◽  
Temperature Dependent

scholarly journals Atmospheric Moisture and Cloud Cover Characteristics Forecast by AMPS*

2008 ◽  
Vol 23 (5) ◽  
pp. 914-930 ◽  
Author(s):  
Ryan L. Fogt ◽  
David H. Bromwich
Keyword(s):  
Liquid Water ◽  
Cloud Cover ◽  
Supercooled Liquid ◽  
South Pole ◽  
Atmospheric Moisture ◽  
Microphysics Scheme ◽  
Low Level ◽  
High Level ◽  
Cloud Ice ◽  
Moisture Variability

Abstract Antarctic Mesoscale Prediction System (AMPS) forecasts of atmospheric moisture and cloud fraction (CF) are compared with observations at McMurdo and Amundsen–Scott South Pole station (hereafter, South Pole station) in Antarctica. Overall, it is found that the model produces excessive moisture at both sites in the mid- to upper troposphere because of a weaker vertical decrease of moisture in AMPS than observed. Correlations with observations suggest AMPS does a reasonable job of capturing the low-level moisture variability at McMurdo and the upper-level moisture variability at South Pole station. The model underpredicts the cloud cover at both locations, but changes to the AMPS empirical CF algorithm remove this negative bias by more than doubling the weight given to the cloud ice path. A “pseudosatellite” product based on the microphysical quantities of cloud ice and cloud liquid water within AMPS is preliminarily evaluated against Defense Meteorological Satellite Program (DMSP) imagery during summer to examine the broader performance of cloud variability in AMPS. These comparisons reveal that the model predicts high-level cloud cover and movement with fidelity, which explains the good agreement between the modified CF algorithm and the observed CF. However, this product also demonstrates deficiencies in capturing low-level cloudiness over cold ice surfaces primarily related to insufficient supercooled liquid water produced by the microphysics scheme, which also reduces the CF correlation with observations. The results suggest that AMPS predicts the overall CF amount and high cloud variability notably well, making it a reliable tool for longer-term climate studies of these fields in Antarctica.

Antarctic Cloud Property Retrievals from Infrared Radiances

2020 ◽  
Author(s):  
Penny Rowe ◽  
Von Walden ◽  
Matthew Fergoda ◽  
Connor Krill ◽  
Jonathon Gero ◽  
...  
Keyword(s):  
Liquid Water ◽  
Field Experiments ◽  
Climate Models ◽  
Complex Refractive Index ◽  
Supercooled Liquid ◽  
Radiative Properties ◽  
Retrieval Algorithm ◽  
South Pole ◽  
Infrared Radiance ◽  
Cloud Properties

<p>Clouds exert a strong radiative impact on the surface and have complicated effects that are still not well understood, particularly in the Antarctic. The amount of supercooled liquid water in Antarctic clouds, for example, is still poorly constrained, due to the low number of observations on the continent. It is also not clear how the radiative properties of supercooled liquid in those clouds should be represented in climate models. In particular, the complex refractive index (CRI) of liquid water is known to depend on temperature, but this dependence is typically ignored in climate models.</p><p>Here, we present cloud properties retrieved from Antarctic downwelling infrared radiance measurements made by an Atmospheric Emitted Radiance Interferometer (AERI) and by the Polar AERI (PAERI), using the CLoud and Atmospheric Radiation Retrieval Algorithm (CLARRA). Preliminary retrievals were made of cloud height, optical depth, thermodynamic phase, and effective radius for field experiments at Amundsen-Scott South Pole Station (2001) and at McMurdo Station (2016).</p><p>At South Pole, we find that clouds are typically thin and near the surface, in keeping with prior work. For thin clouds, the mode of the effective radii of liquid droplets (~4 μm) and ice particles (~15 μm in summer, ~12 μm in winter) at South Pole are found to be smaller than typical Arctic values (~9 μm for liquid and 17 to 25 μm for ice). Although ice cloud was found to dominate year-round at South Pole, significant supercooled liquid water was present in the summer. Cloud properties retrieved at South Pole will be compared to retrievals from McMurdo.</p><p>We further find that ignoring the temperature dependence of the CRI of supercooled liquid cloud leads to negative biases in part of the atmospheric window region (700 – 1000 cm<sup>-1</sup>), indicating underestimation of the greenhouse effect. These biases are expected to be partially offset by positive biases below 600 cm<sup>-1</sup>. Based on these considerations, we recommend using temperature-dependent CRI for infrared radiance simulations of supercooled liquid water cloud.</p>

In Situ Analysis of Surface Contaminant Desorption during Low-Temperature Silicon Substrate Cleaning using Reflection Electron Energy Loss Spectrometry

1992 ◽  
Vol 259 ◽  
Author(s):  
Selmer S. Wong ◽  
Shouleh Nikzad ◽  
Channing C. Ahn ◽  
Aimee L. Smith ◽  
Harry A. Atwater
Keyword(s):  
Low Temperature ◽  
Energy Loss ◽  
Electron Energy ◽  
Core Loss ◽  
Temperature Dependent ◽  
Electron Energy Loss Spectrometry ◽  
Analysis Technique ◽  
Chemical Analysis Technique ◽  
Electron Energy Loss

ABSTRACTWe have employed reflection electron energy loss spectrometry (REELS), a surface chemical analysis technique, in order to analyze contaminant coverages at the submonolayer level during low-temperature in situ cleaning of hydrogen-terminated Si(100). The chemical composition of the surface was analyzed by measurements of the C K, O K and Si L2,3 core loss intensities at various stages of the cleaning. These results were quantified using SiC(100) and SiO2 as reference standards for C and O coverage. Room temperature REELS core loss intensity analysis after sample insertion reveals carbon at fractional monolayer coverage. We have established the REELS detection limit for carbon coverage to be 5±2% of a monolayer. A study of temperature-dependent hydrocarbon desorption from hydrogen-terminated Si(100) reveals the absence of carbon on the surface at temperatures greater than 200°C. This indicates the feasibility of epitaxial growth following an in situ low-temperature cleaning and also indicates the power of REELS as an in situ technique for assessment of surface cleanliness.

scholarly journals A Three-Year Climatology of Cloud-Top Phase over the Southern Ocean and North Pacific

2011 ◽  
Vol 24 (9) ◽  
pp. 2405-2418 ◽  
Author(s):  
Anthony E. Morrison ◽  
Steven T. Siems ◽  
Michael J. Manton
Keyword(s):  
Southern Ocean ◽  
Liquid Water ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Supercooled Liquid ◽  
Global Climate Models ◽  
Shortwave Radiation ◽  
Orthogonal Polarization ◽  
Temperature Range ◽  
Cloud Tops

Abstract Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2 observations from the Terra satellite are used to create a 3-yr climatology of cloud-top phase over a section of the Southern Ocean (south of Australia) and the North Pacific Ocean. The intent is to highlight the extensive presence of supercooled liquid water over the Southern Ocean region, particularly during summer. The phase of such clouds directly affects the absorbed shortwave radiation, which has recently been found to be “poorly simulated in both state-of-the-art reanalysis and coupled global climate models” (Trenberth and Fasullo). The climatology finds that supercooled liquid water is present year-round in the low-altitude clouds across this section of the Southern Ocean. Further, the MODIS cloud phase algorithm identifies very few glaciated cloud tops at temperatures above −20°C, rather inferring a large portion of “uncertain” cloud tops. Between 50° and 60°S during the summer, the albedo effect is compounded by a seasonal reduction in high-level cirrus. This is in direct contrast to the Bering Sea and Gulf of Alaska. Here MODIS finds a higher likelihood of observing warm liquid water clouds during summer and a reduction in the relative frequency of cloud tops within the 0° to −20°C temperature range. As the MODIS cloud phase product has limited ability to confidently identify cloud-top phase between −5° and −25°C, future research should include observations from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and other space-based sensors to help with the classification within this temperature range. Further, multiregion in situ verification of any remotely sensed observations is vital to further understanding the cloud phase processes.

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