Most cirrus clouds are present over the equator and tropical continents.
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Satellite observations indicate that cirrus clouds frequently occur and have high maximum-occurrence frequencies in the upper tropical troposphere and near the tropics, but studies also locate significant occurrences in midlatitudes.
Data from the Lidar In‐Space Technology Experiment (LITE) were used to locate clouds near the equatorial tropopause and retrieve temperatures in cloud layers. The experiment was conducted aboard the space shuttle Discovery on September 9–20, 1994. LITE observations over the equator frequently exhibit cloud layers near the tropopause with scattering ratios as high as 2.5 at 532 nm. These clouds have been characterized as cirrus and subvisible cirrus. The clouds were observed near the tropopause with cloud top temperatures ranging from 185 to 200 K. Statistical averages of two optical properties observed by LITE in the 5°N to 15°S latitude band, the wavelength dependence of the extinction due to aerosols (Angstrom coefficient) and scattering ratios, were computed. The Angstrom coefficients show that a significant number (31%) of these high‐altitude cirrus clouds observed by LITE in the 5°N to 15°S latitude band have optical similarities to type 1a polar stratospheric cloud (PSC) particles. Sixty‐six percent of the clouds observed are thin, with scattering ratios ranging from 1.1 to 1.5. Since these clouds are most likely to form at temperatures of 185±2.5 K (a 90% chance), particles of a size and composition similar to type 1a PSCs must be considered a possibility. Since these high‐altitude tropical cirrus clouds may have significant implications for both ozone chemistry and radiative transfer, a closer examination of their composition and phase (using, for example, both in situ methods and depolarization lidar) together with simultaneous meteorological measurements are needed.
Global distributions of cirrus clouds determined from SAGE data - NASA Technical Reports Server (NTRS)
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Global distributions of cirrus clouds determined from SAGE dataResults are presented from analyses that use SAGE (Stratospheric Aerosol and Gas Experiment) data to determine the spatial extent and frequency of cirrus clouds over much of the earth's surface. The analyses pertain to a period of 15 months extending from February 1979 to April 1980. The results are compared with those from a climatology of ground-based cirrus cloud observations (Hahn et al., 1982). It is found that optically thick cirrus clouds are most often found in the midlatitudes and over the tropics, with distinct minima near the + or - 20 to 30 deg latitude bands. On the other hand, thin cirrus clouds occur much less often than the optically thick cirrus clouds. The comparison of the SAGE cirrus cloud results made zonally with those obtained from ocean-surface-based observations reveals general agreement. Tropospheric observational opportunities for a limb sounding satellite sensor, as evidenced by suc
To investigate the characteristics of Spinning Enhanced Visible and Infrared Imager (SEVIRI)-derived products from the UK Met Office algorithm, one year of cloud occurrence frequency (COF) and cloud-top height (CTH) data from May 2013 to April 2014 was analysed in comparison with Cloud Profiling Radar (CPR) and Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP) cloud products observed from the A-Train constellation. Because CPR operated in daylight-only data collection mode, daytime products were validated in this study. It is important to note that the different sensor characteristics cause differences in CTH retrievals. The CTH of active instruments, CPR and CALIOP, is derived from the return time of the backscattered radar or LiDAR signal, while the infrared sensor, SEVIRI, measures a radiatively effective CTH. Therefore, some systematic differences in comparison results are expected. However, similarities in spatial distribution and seasonal variability of COFs were noted among SEVIRI, CALIOP, and CPR products, although COF derived by the SEVIRI algorithm showed biases of 14.35% and −3.90% compared with those from CPR and CALIOP measurements, respectively. We found that the SEVIRI algorithm estimated larger COF values than the CPR product, especially over oceans, whereas smaller COF was detected by SEVIRI measurements over land and in the tropics than by CALIOP, where multi-layer clouds and thin cirrus clouds are dominant. CTHs derived from SEVIRI showed better agreement with CPR than with CALIOP. Further comparison with CPR showed that SEVIRI CTH was highly sensitive to the CO2 bias correction used in the Minimum Residual method. Compared with CPR CTHs, SEVIRI has produced stable CTHs since the bias correction update in November 2013, with a correlation coefficient of 0.93, bias of −0.27 km, and standard deviation of 1.61 km.
High Resolution Dynamics Limb Sounder (HIRDLS) and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) measurements of cirrus frequency of occurrence in the upper tropical troposphere are quantified for September 2006 to August 2007. Monthly geospatial averages of cloud frequency of occurrence between 90 and 177 hPa are similar and correlate well with Microwave Limb Sounder (MLS) relative humidity with respect to ice (RHI) data, though clouds are present at individual RHI values less than 100%, due to the 5, 1, and sub‐1 km vertical resolutions of the MLS, HIRDLS, and CALIPSO experiments. Seasonal variations in cloud frequency of occurrence are similar, with largest frequencies during winter (December–February). Though the CALIPSO and HIRDLS experiments employ nadir‐ and limb‐viewing observational geometries, respectively, CALIPSO horizontal scales of cirrus are frequently larger than 100 km, and therefore similarities are present in the geospatial distributions of cloud occurrence. Isolated laminar cirrus is most prevalent away from the equator. The monthly patterns of HIRDLS and CALIPSO cloud occurrence are archived for useful comparisons to climate models.
The major pathway for air entering the stratosphere is over the Tropical Western Pacific (TWP) region, and this key region influences the atmospheric composition in the stratosphere. Motivated by this, we used trace gas measurements by using the Fourier Transform Infrared (FTIR) Spectrometer and cirrus cloud measurements by using a ground-based COMpact Cloud Aerosol Lidar, COMCAL from the atmospheric observatory at Koror, Palau (7.34°N, 134.47°E}, in the heart of the Pacific warm pool) and combined model simulations to study the transport pathways, with a special focus on the stratosphere-troposphere exchange (STE) processes over this key region. The atmospheric transport dynamics in the TWP region are closely linked to the movements of the circulation system, particularly the Inter-Tropical Convergence Zone (ITCZ) associated with the up-welling branch of the Hadley cell. Given the limitations of traditional ITCZ indicators, such as the maximum tropical rain belt to determine the air mass origins, I have developed a tool termed the Chemical Equator (CE), modified from Hamilton et al., (2008) to study the Inter-hemispheric Transport (IHT). The CE is calculated by the model simulation of an artificial passive tracer by GEOS-Chem to discern the migration patterns of circulation systems and air mass origins. Subsequently, the CE was used to characterize tropospheric carbon monoxide (CO) and ozone (O3) column measurements using the FTIR Spectrometer and the ozone sondes, respectiv
Global characterization of cirrus clouds using CALIPSO data | NASA Airborne Science Program
# Global characterization of cirrus clouds using CALIPSO data
Nazaryan, H., M.P. McCormick, and W.P. Menzel (2008), Global characterization of cirrus clouds using CALIPSO data, J. Geophys. Res., 113, D16211, doi:10.1029/2007JD009481.
Abstract
A global and seasonal distribution of cirrus clouds is presented herein on the basis of measurements made by the lidar aboard the Earth-orbiting Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite launched in April 2006. The latitude-longitude and vertical distributions of occurrence frequency of cirrus clouds measured by CALIPSO from June 2006 to June 2007 are presented. The investigation of top-layer cirrus clouds shows maximum-occurrence frequency of up to 70% near the tropics over the 100°–180°E longitude band. The results show large latitudinal movement of cirrus cloud cover with the changing seasons. The examination of the vertical distribution of cirrus clouds shows the maximum of cirrus top-altitude occurrence frequency of approximately 11% at 16 km in the tropics. There are no significant differences in ve
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