Editing Cloud physics (section)

== Determination of properties ==

Satellites are used to gather data about cloud properties and other information such as Cloud Amount, height, IR emissivity, visible optical depth, icing, effective particle size for both liquid and ice, and cloud top temperature and pressure.

=== Detection ===
Data sets regarding cloud properties are gathered using satellites, such as [[Moderate-Resolution Imaging Spectroradiometer|MODIS]], [[POLDER]], [[CALIPSO]] or [[European Remote-Sensing Satellite|ATSR]]. The instruments measure the [[radiance]]s of the clouds, from which the relevant parameters can be retrieved. This is usually done by using [[Inverse problem|inverse theory]].<ref name = "2013stubenrauch">{{cite journal |doi=10.1175/BAMS-D-12-00117.1 |title=Assessment of Global Cloud Datasets from Satellites: Project and Database Initiated by the GEWEX Radiation Panel |journal=[[Bulletin of the American Meteorological Society]] |volume=94 |issue=7 |pages=1031–49 |year=2013 |last1=Stubenrauch |first1=C. J |last2=Rossow |first2=W. B |last3=Kinne |first3=S |last4=Ackerman |first4=S |last5=Cesana |first5=G |last6=Chepfer |first6=H |last7=Di Girolamo |first7=L |last8=Getzewich |first8=B |last9=Guignard |first9=A |last10=Heidinger |first10=A |last11=Maddux |first11=B. C |last12=Menzel |first12=W. P |last13=Minnis |first13=P |last14=Pearl |first14=C |last15=Platnick |first15=S |last16=Poulsen |first16=C |last17=Riedi |first17=J |last18=Sun-Mack |first18=S |last19=Walther |first19=A |last20=Winker |first20=D |last21=Zeng |first21=S |last22=Zhao |first22=G |bibcode=2013BAMS...94.1031S |url=https://hal.archives-ouvertes.fr/hal-01091218/document |hdl=2060/20120014334 |s2cid=12145499 |hdl-access=free }}</ref>

The method of detection is based on the fact that the clouds tend to appear brighter and colder than the land surface. Because of this, difficulties rise in detecting clouds above bright (highly [[Reflection (physics)|reflective]]) surfaces, such as oceans and ice.<ref name = "2013stubenrauch" />

=== Parameters ===

The value of a certain parameter is more reliable the more satellites are measuring the said parameter. This is because the range of errors and neglected details varies from instrument to instrument. Thus, if the analysed parameter has similar values for different instruments, it is accepted that the true value lies in the range given by the corresponding data sets.<ref name = "2013stubenrauch" />

The [[Global Energy and Water Cycle Experiment]] uses the following quantities in order to compare data quality from different satellites in order to establish a reliable quantification of the properties of the clouds:<ref name = "2013stubenrauch" />

*the ''[[cloud cover]] or cloud amount'' with values between 0 and 1
*the ''cloud temperature at [[cloud top]]'' ranging from 150 to 340 K
*the ''cloud pressure at top'' 1013 - 100 [[hPa]]
*the ''cloud height'', measured above sea level, ranging from 0 to 20&nbsp;km
*the ''cloud [[Infrared|IR]] [[emissivity]]'', with values between 0 and 1, with a global average around 0.7
*the ''effective cloud amount'', the cloud amount weighted by the cloud IR emissivity, with a global average of 0.5
*the ''cloud (visible) [[optical depth]]'' varies within a range of 4 and 10. 
*the ''cloud water path'' for the liquid and solid (ice) phases of the cloud particles
*the ''cloud effective particle size'' for both liquid and ice, ranging from 0 to 200 μm

=== Icing ===
Another vital property is the icing characteristic of various cloud genus types at various altitudes, which can have great impact on the safety of flying. The methodologies used to determine these characteristics include using CloudSat data for the analysis and retrieval of icing conditions, the location of clouds using cloud geometric and reflectivity data, the identification of cloud types using cloud classification data, and finding vertical temperature distribution along the CloudSat track (GFS).<ref name="Verification of WAFS"/>

The range of temperatures that can give rise to icing conditions is defined according to cloud types and altitude levels:
:Low-level stratocumulus and stratus can cause icing at a temperature range of 0 to -10&nbsp;°C.
:For mid-level altocumulus and altostratus, the range is 0 to -20&nbsp;°C.
:Vertical or multi-level cumulus, cumulonimbus, and nimbostatus, create icing at a range of 0 to -25&nbsp;°C.
:High-level cirrus, cirrocumulus, and cirrostratus generally cause no icing because they are made mostly of ice crystals colder than -25&nbsp;°C.<ref name="Verification of WAFS">{{cite web |url= http://www.icao.int/safety/meteorology/WAFSOPSG/Seminars%20and%20Workshops/WAFC%20Science%20Coordination%20Meeting/Presentations/Verification%20of%20WAFS%20Icing%20Products.pdf|title=Verification of WAFS Icing Products |author=NOAA/ESRL/GSD Forecast Verification Section |year=2009 |access-date=11 November 2014}}</ref>

=== Cohesion and dissolution ===
There are forces throughout the homosphere (which includes the troposphere, stratosphere, and mesosphere) that can impact the structural integrity of a cloud.  It has been speculated that as long as the air remains saturated, the natural force of cohesion that hold the molecules of a substance together may act to keep the cloud from breaking up.  However, this speculation has a logical flaw in that the water droplets in the cloud are not in contact with each other and therefore not satisfying the condition required for the intermolecular forces of cohesion to act.  Dissolution of the cloud can occur when the process of adiabatic cooling ceases and upward lift of the air is replaced by [[Subsidence (atmosphere)|subsidence]].  This leads to at least some degree of adiabatic warming of the air which can result in the cloud droplets or crystals turning back into invisible water vapor.<ref name="cloud droplets">{{cite book |work=[[The Westminster Review]] |title= Constitution of Matter |year=1841|publisher=Baldwin, Cradock, and Joy|page = 43 |url=https://books.google.com/books?id=-yegAAAAMAAJ&pg=RA1-PA43}}</ref> Stronger forces such as wind shear and downdrafts can impact a cloud, but these are largely confined to the troposphere where nearly all the Earth's weather takes place.<ref name="Troposphere">{{cite web |editor=UCAR Center for Science Education|title= The Troposphere – overview |year=2011 |url=http://scied.ucar.edu/shortcontent/troposphere-overview |access-date=15 January 2015}}</ref> A typical cumulus cloud weighs about 500 metric tons, or 1.1 million pounds, the weight of 100 elephants.<ref name="mentalfloss.com">{{cite web | url=http://mentalfloss.com/article/49786/how-much-does-cloud-weigh | title=How Much Does a Cloud Weigh? | website=[[Mental Floss]] | date=April 4, 2013 | access-date=February 5, 2018 | author=Soniak, Matt }}</ref>