scholarly journals Contrails to Cirrus—Morphology, Microphysics, and Radiative Properties

2006 ◽  
Vol 45 (1) ◽  
pp. 5-19 ◽  
Author(s):  
David Atlas ◽  
Zhien Wang ◽  
David P. Duda
Keyword(s):  
Satellite Image ◽  
Radiative Properties ◽  
Time Of Arrival ◽  
Regional Warming ◽  
Optical Extinction ◽  
Essentially Normal ◽  
Minimum Age ◽  
Ground Based Lidar ◽  
Time Of Travel ◽  
Ice Water

Abstract This work is two pronged, discussing 1) the morphology of contrails and their transition to cirrus uncinus, and 2) their microphysical and radiative properties. It is based upon the fortuitous occurrence of an unusual set of essentially parallel contrails and the unanticipated availability of nearly simultaneous observations by photography, satellite, automated ground-based lidar, and a newly available database of aircraft flight tracks. The contrails, oriented from the northeast to southwest, are carried to the southeast with a component of the wind so that they are spread from the northwest to southeast. Convective turrets form along each contrail to form the cirrus uncinus with fallstreaks of ice crystals that are oriented essentially normal to the contrail length. Each contrail is observed sequentially by the lidar and tracked backward to the time and position of the originating aircraft track with the appropriate component of the wind. The correlation coefficient between predicted and actual time of arrival at the lidar is 0.99, so that one may identify both visually and satellite-observed contrails exactly. Contrails generated earlier in the westernmost flight corridor occasionally arrive simultaneously with those formed later closer to the lidar to produce broader cirrus fallstreaks and overlapping contrails on the satellite image. The minimum age of a contrail is >2 h and corresponds to the longest time of travel to the lidar. The lag between the initial formation of the contrail and its first detectability by Moderate-Resolution Imaging Spectroradiometer (MODIS) is ≈33 min, thus accounting for the distance between the aircraft track and the first detectable contrail by satellite. The lidar also provides particle fall speeds and estimated sizes, optical extinction coefficients, optical thickness (τ = 0.35), and ice water path (IWP = 8.1 g m−2). These values correspond to the lower range of those found for midlatitude cirrus by Heymsfield et al. The ice water per meter of length along the cloud lines is 103–104 times that released by typical jet aircraft. The synthesis of these findings with those of prior investigators provides confidence in the present results. Various authors find that contrail-generated cirrus such as reported here contribute to net regional warming.

scholarly journals Inventory of glaciers in isla Riesco, Patagonia, Chile, based on aerial photography and satellite imagery

2002 ◽  
Vol 34 ◽  
pp. 373-378 ◽  
Author(s):  
Gino Casassa ◽  
Katrine Smith ◽  
Andrés Rivera ◽  
José Araos ◽  
Michael Schnirch ◽  
...  
Keyword(s):  
Supervised Classification ◽  
Satellite Image ◽  
Aerial Photographs ◽  
Glacier Area ◽  
Regional Warming ◽  
Glacier Inventory ◽  
Tm Image ◽  
Chilean Patagonia ◽  
Precipitation Decrease ◽  
Area Data

AbstractA glacier inventory for península Córdova, isla Riesco, Chilean Patagonia (53°14’ S, 73°00’W), has been compiled based on stereoscopic interpretation of aerial photographs of March and December 1984 and 1:100 000 topographic maps. Three small icefields comprising 33 glacier outlets, in addition to 12 small separate glaciers, have been identified, with a total area of 57 km2. Glaciers are located on mountain peaks with a maximum altitude of 1183 mand a lowermost elevation of 100 m. All glaciers terminate on land, except for three glaciers calving into small fresh-water lakes. A Landsat Thematic Mapper (TM) image of 6 October 1986 has been rectified and analyzed using a supervised classification to estimate snow- and glacier-covered surfaces. Glacier-area data derived from satellite-image analyses have been adjusted at península Córdova using photo-interpreted data, and extrapolated to estimate a glacier area of 215 ±40km2 for all of isla Riesco. The presence of trimlines and moraines beyond the present position of the glaciers indicates a generalized retreat from a maximum neoglacial position at península Córdova, most probably as a result of regional warming and precipitation decrease observed during the last century.

Independent Evaluation of the Ability of Spaceborne Radar and Lidar to Retrieve the Microphysical and Radiative Properties of Ice Clouds

2006 ◽  
Vol 23 (2) ◽  
pp. 211-227 ◽  
Author(s):  
Robin J. Hogan ◽  
Malcolm E. Brooks ◽  
Anthony J. Illingworth ◽  
David P. Donovan ◽  
Claire Tinel ◽  
...  
Keyword(s):  
Particle Size ◽  
Water Content ◽  
Multiple Scattering ◽  
Optical Depth ◽  
Radiative Properties ◽  
Molecular Scattering ◽  
Retrieval Algorithms ◽  
Ice Water Content ◽  
Ice Water ◽  
Better Than

Abstract The combination of radar and lidar in space offers the unique potential to retrieve vertical profiles of ice water content and particle size globally, and two algorithms developed recently claim to have overcome the principal difficulty with this approach—that of correcting the lidar signal for extinction. In this paper “blind tests” of these algorithms are carried out, using realistic 94-GHz radar and 355-nm lidar backscatter profiles simulated from aircraft-measured size spectra, and including the effects of molecular scattering, multiple scattering, and instrument noise. Radiation calculations are performed on the true and retrieved microphysical profiles to estimate the accuracy with which radiative flux profiles could be inferred remotely. It is found that the visible extinction profile can be retrieved independent of assumptions on the nature of the size distribution, the habit of the particles, the mean extinction-to-backscatter ratio, or errors in instrument calibration. Local errors in retrieved extinction can occur in proportion to local fluctuations in the extinction-to-backscatter ratio, but down to 400 m above the height of the lowest lidar return, optical depth is typically retrieved to better than 0.2. Retrieval uncertainties are greater at the far end of the profile, and errors in total optical depth can exceed 1, which changes the shortwave radiative effect of the cloud by around 20%. Longwave fluxes are much less sensitive to errors in total optical depth, and may generally be calculated to better than 2 W m−2 throughout the profile. It is important for retrieval algorithms to account for the effects of lidar multiple scattering, because if this is neglected, then optical depth is underestimated by approximately 35%, resulting in cloud radiative effects being underestimated by around 30% in the shortwave and 15% in the longwave. Unlike the extinction coefficient, the inferred ice water content and particle size can vary by 30%, depending on the assumed mass–size relationship (a problem common to all remote retrieval algorithms). However, radiative fluxes are almost completely determined by the extinction profile, and if this is correct, then errors in these other parameters have only a small effect in the shortwave (around 6%, compared to that of clear sky) and a negligible effect in the longwave.

scholarly journals Sensitivity of radiative properties of persistent contrails to the ice water path

2011 ◽  
Vol 11 (7) ◽  
pp. 19927-19952
Author(s):  
R. Rodríguez De León ◽  
M. Krämer ◽  
D. S. Lee ◽  
J. C. Thelen
Keyword(s):  
Water Content ◽  
Radiative Properties ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Large Variability ◽  
Water Path ◽  
Ice Water Path ◽  
Ice Water Content ◽  
Ice Water

Abstract. The dependence of the radiative properties of persistent linear contrails on the variability of their ice water path is assessed in a two-stream radiative transfer model. It is assumed that the ice water content and the effective size of ice crystals in aged contrails do not differ from those observed in natural cirrus; the parameterization of these two variables, based on in situ observations, allows a more realistic representation than the common assumption of fixed values for the contrail optical depth and ice crystal effective radius. The results show that the large variability in ice water content that aged contrails may share with natural cirrus, together with an assumed contrail vertical thickness between 220 and 1000 m, translate into a wider range of radiative forcings from linear contrails (0.3 to 51.6 mW m−2) than that reported in previous studies, including IPCC's (3 to 30 mW m−2). The derivation of a best estimate within this range is complicated by the fact that the ice water contents measured in situ imply mean optical depths between 0.08 and 0.32, coinciding with the range commonly assumed in contrail studies, while optical depths derived from satellite ice water content retrievals are significantly larger (0.51–2.02). Further field and modelling studies of the temporal evolution of contrail properties will thus be needed to reduce the uncertainties associated with the values assumed in large scale contrail studies.

scholarly journals Ice water content of arctic, midlatitude, and tropical cirrus – Part 2: Extension of the database and new statistical analysis

2012 ◽  
Vol 12 (11) ◽  
pp. 29443-29474 ◽  
Author(s):  
A. E. Luebke ◽  
L. M. Avallone ◽  
C. Schiller ◽  
C. Rolf ◽  
M. Krämer
Keyword(s):  
Water Content ◽  
Radiative Forcing ◽  
Climate Models ◽  
Distribution Functions ◽  
Formation Mechanisms ◽  
Mean Values ◽  
Microphysical Properties ◽  
Ice Water Content ◽  
Ground Based Lidar ◽  
Ice Water

Abstract. Ice clouds are known to be major contributors to radiative forcing in the Earth's atmosphere, yet describing their microphysical properties in climate models remains challenging. Among these properties, the ice water content (IWC) of cirrus clouds is of particular interest both because it is measurable and because it can be directly related to a number of other radiatively important variables such as extinction and effective radius. This study expands upon the work of Schiller et al. (2008), extending a climatology of IWC by combining datasets from several European and US airborne campaigns and ground-based lidar measurements over Jülich, Germany. The relationship between IWC and temperature is further investigated using the new merged dataset and probability distribution functions (PDFs). A PDF-based formulation allows for representation of not only the mean values of IWC, but also the variability of IWC within a temperature band. The IWC-PDFs are found to be bimodal over the whole cirrus temperature range, which might be attributed to different cirrus formation mechanisms such as heterogeneous and homogeneous freezing. The PDFs of IWC are further compared to distributions of cirrus ice crystal number and mass mean radius, which show that the general relationship between IWC and temperature appears to be influenced much more by particle number than by particle size.

scholarly journals Cloudnet

2007 ◽  
Vol 88 (6) ◽  
pp. 883-898 ◽  
Author(s):  
A. J. Illingworth ◽  
R. J. Hogan ◽  
E.J. O'Connor ◽  
D. Bouniol ◽  
M. E. Brooks ◽  
...  
Keyword(s):  
Climate Models ◽  
Field Studies ◽  
Radiative Properties ◽  
Systematic Evaluation ◽  
Vertical Profiles ◽  
Dual Frequency ◽  
Cloud Properties ◽  
Analysis Scheme ◽  
Depth Analysis ◽  
Ice Water

The Cloudnet project aims to provide a systematic evaluation of clouds in forecast and climate models by comparing the model output with continuous ground-based observations of the vertical profiles of cloud properties. In the models, the properties of clouds are simplified and expressed in terms of the fraction of the model grid box, which is filled with cloud, together with the liquid and ice water content of the clouds. These models must get the clouds right if they are to correctly represent both their radiative properties and their key role in the production of precipitation, but there are few observations of the vertical profiles of the cloud properties that show whether or not they are successful. Cloud profiles derived from cloud radars, ceilometers, and dual-frequency microwave radiometers operated at three sites in France, Netherlands, and the United Kingdom for several years have been compared with the clouds in seven European models. The advantage of this continuous appraisal is that the feedback on how new versions of models are performing is provided in quasi-real time, as opposed to the much longer time scale needed for in-depth analysis of complex field studies. Here, two occasions are identified when the introduction of new versions of the ECMWF and Météo-France models leads to an immediate improvement in the representation of the clouds and also provides statistics on the performance of the seven models. The Cloudnet analysis scheme is currently being expanded to include sites outside Europe and further operational forecasting and climate models.

scholarly journals Obtaining Best Estimates for the Microphysical and Radiative Properties of Tropical Ice Clouds from TWP-ICE In Situ Microphysical Observations

2011 ◽  
Vol 50 (4) ◽  
pp. 895-915 ◽  
Author(s):  
A. Protat ◽  
G. M. McFarquhar ◽  
J. Um ◽  
J. Delanoë
Keyword(s):  
Total Concentration ◽  
Radiative Properties ◽  
Size Distributions ◽  
Maximum Dimension ◽  
Ice Clouds ◽  
Ice Water Content ◽  
Ice Water ◽  
The Impact ◽  
Total Concentrations

AbstractBest estimates of the bulk microphysical and radiative properties (ice water content, visible extinction, effective radius, and total concentration) are derived for three case studies of tropical ice clouds sampled during the Tropical Warm Pool International Cloud Experiment (TWP-ICE). Two case studies are aged cirrus clouds produced by deep convection (the so-called 27/01 and 29/01 cases), and the third (“02/02”) is a fresh anvil produced by deep convective activity over the Tiwi Islands. Using crystal images obtained by a Cloud Particle Imager (CPI), it is observed that small ice particles (with maximum dimension D < 50–100 μm) were predominantly quasi spherical, with the degree of nonsphericity increasing rapidly in the 50 < D < 100-μm range. For D > 100 μm, the aged cirrus clouds were predominantly characterized by bullet rosettes and aggregates of bullet rosettes, plates, and columns. In contrast, the fresh anvil had more frequent occurrences of plates, columns, aggregates of plates, and occasionally capped columns. The impact of shattering of large ice crystals on probe tips and the overall quality of the TWP-ICE in situ microphysical measurements are assessed. It is suggested that shattering has a relatively small impact on the CPI and cloud droplet probe (CDP) TWP-ICE data and a large impact on the Cloud Aerosol Spectrometer data, as already documented by others. It is also shown that the CPI size distributions must be multiplied by a factor of 4 to match those of the cloud imaging probe (CIP) for maximum dimension larger than 100 μm (taken as a reference). A technique [named Best Estimate of Area and Density (BEAD)] to minimize errors associated with the density (ρ)–D and projected area (A)–D assumptions in bulk microphysics calculation is introduced and applied to the TWP-ICE data. The method makes direct use of the frequency of occurrence of each particle habit as classified from the CPI data and prescribed ρ–D and A–D relationships from the literature. This approach produces ice water content (IWC) estimates that are virtually unbiased relative to bulk measures obtained from a counterflow spectrometer and impactor (CSI) probe. In contrast, the use of ρ–D and A–D relationships for single habits does produce large biases relative to the CSI observations: from −50% for bullet rosettes to +70%–80% for aggregates. The so-called width, length, area, and perimeter (WLAP) technique, which also makes use of individual CPI images, is found to produce positively biased IWCs (by 40% or so), and has a standard deviation of the errors similar to the BEAD technique. The impact of the large variability of the size distributions measured by different probe combinations on the bulk microphysical properties is characterized. The mean fractional differences with respect to the CSI measurements are small for the CPI + CIP, CPI, and CDP + CIP combinations (2.2%, −0.8%, and −1.1%, respectively), with standard deviations of the fractional differences ranging from 7% to 9%. This result provides an independent validation of the CPI scaling factor. The fractional differences produced between the CPI + CIP, CPI, and CDP + CIP combinations for extinction, effective radius, and total concentration are 33%, 10%–20%, and 90%, respectively, with relatively small standard deviations of 5%–8%. The fractional difference on total concentration varies greatly over the concentration range though, with values being larger than a factor of 2 for total concentrations smaller than 40 L−1, but reducing to 10%–20% for concentrations larger than 100 L−1. Therefore, caution should be exercised when using total concentrations smaller than 60–80 L−1 as references for radar–lidar retrieval evaluation.

scholarly journals Ice water content of Arctic, midlatitude, and tropical cirrus – Part 2: Extension of the database and new statistical analysis

2013 ◽  
Vol 13 (13) ◽  
pp. 6447-6459 ◽  
Author(s):  
A. E. Luebke ◽  
L. M. Avallone ◽  
C. Schiller ◽  
J. Meyer ◽  
C. Rolf ◽  
...  
Keyword(s):  
Water Content ◽  
Radiative Forcing ◽  
Climate Models ◽  
Distribution Functions ◽  
Formation Mechanisms ◽  
Mean Values ◽  
Microphysical Properties ◽  
Ice Water Content ◽  
Ground Based Lidar ◽  
Ice Water

Abstract. Ice clouds are known to be major contributors to radiative forcing in the Earth's atmosphere, yet describing their microphysical properties in climate models remains challenging. Among these properties, the ice water content (IWC) of cirrus clouds is of particular interest both because it is measurable and because it can be directly related to a number of other radiatively important variables such as extinction and effective radius. This study expands upon the work of Schiller et al. (2008), extending a climatology of IWC by combining datasets from several European and US airborne campaigns and ground-based lidar measurements over Jülich, Germany. The relationship between IWC and temperature is further investigated using the new merged dataset and probability distribution functions (PDFs). A PDF-based formulation allows for representation of not only the mean values of IWC, but also the variability of IWC within a temperature band. The IWC-PDFs are observed to be bimodal over the whole cirrus temperature range. This bimodality is also found in ice crystal number PDFs and might be attributed to different cirrus formation mechanisms such as heterogeneous and homogeneous freezing.

scholarly journals Ice water content vertical profiles of high-level clouds: classification and impact on radiative fluxes

2015 ◽  
Vol 15 (21) ◽  
pp. 12327-12344 ◽  
Author(s):  
A. G. Feofilov ◽  
C. J. Stubenrauch ◽  
J. Delanoë
Keyword(s):  
Water Content ◽  
Surface Fluxes ◽  
Radiative Properties ◽  
Cloud Base ◽  
Vertical Profiles ◽  
Ice Clouds ◽  
Isosceles Trapezoid ◽  
Ice Water Content ◽  
High Level ◽  
Ice Water

Abstract. In this article, we discuss the shape of ice water content (IWC) vertical profiles in high ice clouds and its effect on their radiative properties, both in short- and in long-wave bands (SW and LW). Based on the analysis of collocated satellite data, we propose a minimal set of primitive shapes (rectangular, isosceles trapezoid, lower and upper triangle), which represents the IWC profiles sufficiently well. About 75 % of all high-level ice clouds (P < 440 hPa) have an ice water path (IWP) smaller than 100 g m−2, with a 10 % smaller contribution from single layer clouds. Most IWC profiles (80 %) can be represented by a rectangular or isosceles trapezoid shape. However, with increasing IWP, the number of lower triangle profiles (IWC rises towards cloud base) increases, reaching up to 40 % for IWP values greater than 300 g m−2. The number of upper triangle profiles (IWC rises towards cloud top) is in general small and decreases with IWP, with the maximum occurrence of 15 % in cases of IWP less than 10 g m−2. We propose a statistical classification of the IWC shapes using IWP as a single parameter. We have estimated the radiative effects of clouds with the same IWP and with different IWC profile shapes for five typical atmospheric scenarios and over a broad range of IWP, cloud height, cloud vertical extent, and effective ice crystal diameter (De). We explain changes in outgoing LW fluxes at the top of the atmosphere (TOA) by the cloud thermal radiance while differences in TOA SW fluxes relate to the De vertical profile within the cloud. Absolute differences in net TOA and surface fluxes associated with these parameterized IWC profiles instead of assuming constant IWC profiles are in general of the order of 1–2 W m−2: they are negligible for clouds with IWP < 30 g m−2, but may reach 2 W m−2 for clouds with IWP > 300 W m−2.

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