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== News == '''2014-06-17''' The 1st workshop of the ICWG (previously referred to as Cloud Retrieval Evaluation Workshops) is tentatively planned to be held in 2016 in Lille, France. '''2014-05-25''' The CREW has been endorsed as International Clouds Working Group (ICWG) within the Coordination Group for Meteorological Satellites (CGMS) at CGMS’s 42nd meeting on 19-23 May 2014 (Guangzhou, China). '''2014-03-18''' CREW 4 took place in Grainau in March 2014. 69 scientist from Europe, America, Asia and Africa participated the workshop. The [[CREW-4_Oral_presentations|'''oral''']] and [[CREW-4_Poster_presentations|'''poster''']] presentations are available on the "Meetings" page of this website. '''2014-03-10''' The [[SEVIRI_Inter-comparison_and_Validation_Software_Package| '''inter-comparison and validation software of the SEVIRI inter-comparison group''']] is available to the CREW participants. '''2014-03-05''' In order to support the discussion of the working groups, a [[Media:Handout_CREW4.pdf| '''CREW 4 handout''']] with recent results from the calibration, inter-comparison and validation and aggregation methods research has been published. Special thanks to all voluntarily contributing authors. '''2014-01-15''' The [http://www.atmos-meas-tech-discuss.net/7/401/2014/amtd-7-401-2014.pdf '''first publication using the CREW database'''] was submitted to AMT. The publications documents the inter-comparison and validation of the SEVIRI cloud top height retrievals.<br> == The motivation == Clouds cover about 70% of the Earth’s surface. They appears in various forms as marine stratocumulus, deep convective clouds in the tropics, frontal systems and many more. On the one hand cloud clouds have a global extent. On the other hand cloud formation is based on micro physics. Cloud droplets and ice crystal sizes are usually in the micro meter range. Temperature, humidity, aerosols and turbulence are critical parameters for cloud growth. The clouds may be described by their macro physical properties (like cloud phase, water content, cloud top and base height) or their optical properties (like cloud optical thickness and effective radius). Cloud influence in several ways atmospheric physics. Clouds play a dominant role in the ''hydrological cycle'' of our planet. By condensations water vapor is removed from the air. Droplets and ice crystals are transported within clouds by convection, are horizontally advected, and precipitation is formed. The phase change of water release latent energy altering small-scale convective or turbulent circulations and the vertical heating profile. Furthermore clouds modify the ''radiative transfer'' through the atmosphere. Clouds reflect a part of the sunlight, this effect cools the earth. They also reduce the amount of thermal radiation emitted to space thus warming the earth. The net effect depends on the cloud properties. For low and middle clouds the cooling effect dominates, while high clouds tend to have a warming effect. Due to their large impact on the energy and water cycle, clouds have to be well represented in weather and climate models. In order to validate these models accurate observations are needed. Where ground based measurements provide information of high accuracy at certain places, satellite observations provide continuous observation of the atmospheric state over the whole globe being indispensable for the validation of global models. == The ICWG == The International Clouds Working Group (ICWG) was established as a permanent Working Group within the [http://www.cgms-info.org/ '''Coordination Group for Meteorological Satellites (CGMS)'''] at CGMS’s 42nd meeting on 19-23 May 2014 (Guangzhou, China). The ICWG is co-sponsored by CGMS and the World Meteorological Organization (WMO). It provides a forum for operational and research users of cloud parameter retrievals that aims to enhance knowledge on quantitative cloud parameter retrievals from state-of-the-art algorithms and identify shortcomings that need focused attention as a community. Continual improvement in the global description of cloud properties optimizes these algorithms for near-term (now-casting), short to medium term (weather forecasting), and long-term (regional and climatological analyses) applications, as well as for potential improvements in the cloud and convection parameterizations adopted in weather and climate models. The objectives of the ICWG include: a) to promote commonality in operational cloud retrieval algorithms; b) to address research questions identified by space agencies and WMO programs (e.g. GEWEX); c) to promote assessments of cloud retrievals; d) to foster adoption of standards, for example validation procedures and data formats; e) to contribute to the definition of new space borne observation capabilities for cloud retrievals and validation; f) to support and stimulate training; g) to enhance the communication in this field and develop international partnerships. The ICWG's predecessor was the Cloud Retrieval Evaluation Working Group that has been organizing Cloud Retrieval Evaluation Workshops (CREWs) since 2006. CREW-1 took place in Norrköping, Sweden from 17 - 19 May 2006, CREW-2 in Locarno, Switzerland from 3 - 5 February 2009, CREW-3 in Madison, Wisconsin, USA from 15 -18 November 2011, and CREW-4 in Grainau, Germany from 4-7 March 2014. These CREWs focused on the evaluation of strengths and weaknesses in the most important algorithms that retrieve cloud properties from passive imager instruments onboard both polar and geostationary satellites (SEVIRI, AVHRR, and MODIS). At the CREWs level-2 cloud parameter retrievals from different providers, for 5 golden days collected in the '''[[CREW Data Set|CREW Common Database]]''', have been inter-compared and validated against observations from the A-train satellite constellation (CALIPSO, CLOUDSAT, and AMSR). More details on the CREW meetings can be found on the '''[[Meetings|Meetings]]''' page. Please note that some document can only be accessed after registration, to register please [mailto:%75%6c%72%69%63%68%2e%68%61%6d%61%6e%6e%40%6d%65%74%65%6f%73%77%69%73%73%2e%63%68;%6a%65%72%6f%6d%65%2e%72%69%65%64%69%40%75%6e%69%76%2d%6c%69%6c%6c%651%2e%66%72 email us] for registration instructions). == The members == The ICWG a forum for operational and research users of cloud parameter retrievals. Since the first workshop in 2006 the workshops have been attended by an increasing number of participants . CREW-1 (hosted by the Swedish Meteorological and Hydrological Institute) was attended by 23 participants, CREW-2 (hosted by Meteo Swiss) by 44 participants, CREW-3 (hosted by University of Wisconsin) by 71 participants, and CREW-4 (hosted by Deutscher Wetterdienst) by 69 participants. == The approach == Currently 13 groups provide data sets of retrieved cloud physical properties, i.e., Cloud mask, cloud fraction, cloud top temperature, cloud top pressure, cloud top height, cloud optical depth, effective radius, cloud water path, cloud type, and convective signature. The data is inter-compared for five days, that were most suitable for validation purposes. == The International Cooperations == We cooperate with the [http://climserv.ipsl.polytechnique.fr/gewexca/ GEWEX - Cloud Assessment] project that rather compares climatologies, whereas CREW is intended for investigating the details of the retrieval algorithms. We are also in contact with the cloud project of the [http://www.esa-cloud-cci.org/ ESA Climate Change Initiative], that aims generate a climatological cloud data set from AVHRR heritage channels. <!--Probably CREW will become a working group of the [http://www.cgms-info.org/ Coordination Group for Meteorological Satellites].--> <center> [http://climserv.ipsl.polytechnique.fr/gewexca/ GEWEX cloud assessment]<br> [[Image:GEWEX-cloud-assessment.png|316x760px|GEWEX cloud assessment|link=http://climserv.ipsl.polytechnique.fr/gewexca/]]<br><br> <!--[http://www.cgms-info.org/ Coordination Group for Meteorological Satellites]<br> [[Image:CGMS_Final.png|316x760px|CGMS]]<br><br>--> [http://www.esa-cloud-cci.org/ ESA Clouds Climate Change Initiative (ESA Cloud CCI)]<br> [[Image:ESA-CCI-clouds.png|316x760px|ESA CCI clouds|link=http://www.esa-cloud-cci.org/]]<br> </center>

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