Studying Global Cloud Cover Changes
Seasonal changes in global cloud cover are being monitored with multi-spectral observations from the fifteen polar orbiting HIRS (High resolution Infrared Radiation Sounder) since December 1978 (Wylie et al 2005). The HIRS longwave infrared data have a higher sensitivity to semi-transparent cirrus clouds than visible and infrared window techniques. Clouds are found in 75% of all HIRS observations from 65 S to 65 N; high clouds are observed in 33% of the observations. Closer investigation of the tropics indicates that there has been little overall change in the global total cloud cover. There is the possibility of a small increase in high cloud cover from the first decade to the second (about 2%) however orbit drift and sensor to sensor differences may be part of this. It appears that high cloud cover changes are mostly caused by larger weather systems. Since 2000, the Moderate resolution Imaging Spectro-radiometer (MODIS) is starting to generate another cloud data set that must be understood and connected with the HIRS cloud data (Menzel et al 2008).
The monthly average frequency of clouds and high clouds (above 6 km) from 70 south to 70 north latitude from 1979 to 2002; Wylie et al. 2005.
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Investigating the cloud properties with high spectral resolution data
Plokhenko and Menzel are studying opportunities for 3-dimensional cloud property characterization using the combination of vertical cloud structure determined by AIRS high spectral resolution infrared measurements and MODIS high horizontal resolution measurements when semi-transparent high clouds cover lower clouds. Using a cloud radiative transfer model wherein cloud amount and cloud top pressure are adjusted in each of 25 levels (spaced to provide uniform vertical resolution as much as possible) to match calculated with measured radiances for the AIRS spectral bands, cloud amount profiles are estimated. Comparisons with Calipso cloud determinations are showing strong agreement; McIDAS-V 3D images are providing interesting depiction of the vertical distribution sof clouds.
Vertical cross-section of CALIPSO cloud detection on 26 August 2008 from 60 S to 20 N latitude (left) with AIRS cloud profiles overlaid (right).
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McV 3D depiction of cloud amount profiles provides evidence of the good continuity from one AIRS field of view to the next.
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Sounding Retrievals in Clouds
Studies have been onging (Li et al 2008) to extend the high temporal resolution Geostationary Operational Environmental Satellite (GOES) infrared sounding retrievals from clear to cloudy skies, a synthetic regression-based cloudy sounding retrieval algorithm has been developed and applied to GOES 12 sounder measurements. Comparisons against radiosondes at the Atmospheric Radiation Measurement Program at Southern Great Plains site from August 2006 to May 2007 and the conventional radiosondes network over the continental United States from January 2007 to November 2008 both show that the retrievals of moisture under thin cloud conditions perform similarly to those under the clear-sky conditions. The largest improvements are found in the upper level integrated precipitable water vapor (PW) or PW3. Also in the case of low thick clouds, PW3 is usually improved significantly. In addition, the retrieved cloud parameters are consistent with the false RGB composite images. With the addition of the soundings under low thick or thin cloud conditions, the area without soundings is reduced by 57% in the selected case. The application to a tornadic storm on 24 April 2007 reveals that the GOES cloudy sounding retrievals are more useful at the early stage of the storm, when nearby clouds are considered thin or broken. The GOES cloudy sounding algorithm reveals more pronounced and extensive convective instability, and it does so earlier than the clear-sky-only results. The cloudy sounding retrievals have the potential to provide an earlier warning to forecasters.
Time series of the derived product imagery of LI on 24 April 2007 at (a–d) 2000 UTC, (e–h) 2100 UTC, (i–l) 2200 UTC, and (m–p) 2300 UTC. Figures a, e, i, and m are for the GFS forecast; Figures b, f, j, and n are for the RUC 6-h forecast; Figures c, g, k, and o are for GOES 12 clear-sky retrievals; and Figures d, h, l, and p are for GOES 12 clear plus cloudy retrievals. Note that the two areas A and B are each associated with convective activity. The area C is associated with a third storm which happened between 0100 and 0200 UTC on 25 April 2007.
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Remote Sensing Lectures
A series of lectures on remote sensing have been offered by Drs Paul Menzel and Paolo Antonelli in New Delhi, India Feb 2011; Sasso di Castaldo, Italy Jul 2009; Perth, Australia Jan 2009; Istanbul, Turkey Oct 2008; Monteponi, Sardenia Sep 2008; Benevento, Italy Jun 2007; Ostuni, Italy Jun 2006; Krakow, Poland May 2006; Bertinoro, Italy Sep 2004, Maratea, Italy May 2003; Rome, Italy Jun 2002; and Bologna, Italy Sep 2001 More than 250 students have attended. The World Meteorological Organization Technical Document "Applications with Meteorological Satellites" authored by Dr. Menzel was used as a text during these lectures. The courses included materials on (a) radiation and the radiative transfer equation, (b) remote sensing of the Earth surface and its atmosphere, (c) instrument considerations, (d) algorithms for detecting and estimating moisture, precipitation, and clouds properties, and (e)ccurrent and future capabilities of the global observing system Fifty hours of classroom work was split between lectures and laboratory exercises that emphasized investigation of high spatial resolution visible and infrared data (from the Moderate resolution Imaging Spectroradiometer, MODIS, and Meteosat Second Generation, MSG), high spectral resolution infrared data (from the Advanced Infrared Sounder, AIRS and the Infrared Atmospheric Sounding Interferometer, IASI), and microwave sounding data (from the Advanced Microwave Sounding Unit, AMSU) . Homework assignments and classroom tests verified that good progress was made in learning and mastering the materials presented.