The Global Distribution of Supersaturation in the Upper Troposphere from the Atmospheric Infrared Sounder

Gettelman, Andrew; Fetzer, Eric J.; Eldering, A.; Irion, F. W.

doi:10.1175/jcli3955.1

Cited by 110 publications

(168 citation statements)

References 36 publications

(53 reference statements)

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“…Ice supersaturated regions (ISSRs), i.e., clear air masses with ice supersaturation, are the potential formation regions for cirrus clouds (Gierens and Spichtinger, 2000;Spichtinger et al, 2003a, b). A variety of data sets (satellite, aircraft, radiosondes) and trajectory calculations serve to improve the understanding of ISSRs and cirrus formation (Ovarlez et al, 2000;Comstock et al, 2004;Jensen et al, 2005;Spichtinger et al, 2005;Gettelman et al, 2006;Vömel et al, 2007;Krämer et al, 2009). Although persistent ISSRs in the upper-tropospheric cloudfree air are well understood, very high supersaturations are difficult to comprehend inside thicker cirrus clouds, such as those described here, with high backscatter ratios of 30-200 (see Fig.…”

Section: A Cirisan Et Al: Balloon-borne Match Measurementsmentioning

confidence: 91%

Balloon-borne match measurements of midlatitude cirrus clouds

et al. 2014

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Abstract.Observations of high supersaturations with respect to ice inside cirrus clouds with high ice water content (> 0.01 g kg −1 ) and high crystal number densities (> 1 cm −3 ) are challenging our understanding of cloud microphysics and of climate feedback processes in the upper troposphere. However, single measurements of a cloudy air mass provide only a snapshot from which the persistence of ice supersaturation cannot be judged. We introduce here the "cirrus match technique" to obtain information about the evolution of clouds and their saturation ratio. The aim of these coordinated balloon soundings is to analyze the same air mass twice. To this end the standard radiosonde equipment is complemented by a frost point hygrometer, "SnowWhite", and a particle backscatter detector, "COBALD" (Compact Optical Backscatter AerosoL Detector). Extensive trajectory calculations based on regional weather model COSMO (Consortium for Small-Scale Modeling) forecasts are performed for flight planning, and COSMO analyses are used as a basis for comprehensive microphysical box modeling (with grid scale of 2 and 7 km, respectively). Here we present the results of matching a cirrus cloud to within 2-15 km, realized on 8 June 2010 over Payerne, Switzerland, and a location 120 km downstream close to Zurich. A thick cirrus cloud was detected over both measurement sites. We show that in order to quantitatively reproduce the measured particle backscatter ratios, the smallscale temperature fluctuations not resolved by COSMO must be superimposed on the trajectories. The stochastic nature of the fluctuations is captured by ensemble calculations. Possibilities for further improvements in the agreement with the measured backscatter data are investigated by assuming a very slow mass accommodation of water on ice, the presence of heterogeneous ice nuclei, or a wide span of (spheroidal) particle shapes. However, the resulting improvements from these microphysical refinements are moderate and comparable in magnitude with changes caused by assuming different regimes of temperature fluctuations for clear-sky or cloudysky conditions, highlighting the importance of proper treatment of subscale fluctuations. The model yields good agreement with the measured backscatter over both sites and reproduces the measured saturation ratios with respect to ice over Payerne. Conversely, the 30 % in-cloud supersaturation measured in a massive 4 km thick cloud layer over Zurich cannot be reproduced, irrespective of the choice of meteorological or microphysical model parameters. The measured supersaturation can only be explained by either resorting to an unknown physical process, which prevents the ice particles from consuming the excess humidity, or -much more likely -by a measurement error, such as a contamination of the sensor housing of the SnowWhite hygrometer by a precipitation drop from a mixed-phase cloud just below the cirrus layer or from some very slight rain in the boundary layer. This uncertainty calls for in-flight checks or calibrations of hygrom...

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Section: A Cirisan Et Al: Balloon-borne Match Measurementsmentioning

confidence: 91%

Balloon-borne match measurements of midlatitude cirrus clouds

et al. 2014

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“…We note that a new UTH w data set can be produced with the same method but we have not yet done that. As we are eventually interested in ice supersaturation (Gierens et al, 2004(Gierens et al, , 2012 we restrict our data currently to a latitude band from 30 to 60 • N, because data from other satellites showed almost no ice supersaturation in the 300-500 hPa layer within the tropical latitude band (see for instance Spichtinger et al, 2003b;Gettelman et al, 2006). The first applications of this new data set are presented in Sect.…”

Section: K Gierens Et Al: 30 Years Of Hirs Data Of Uthmentioning

confidence: 99%

Technical Note: 30 years of HIRS data of upper tropospheric humidity

2014

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Abstract. We use 30 years of intercalibrated HIRS (HighResolution Infrared Radiation Sounder) data to produce a 30-year data set of upper tropospheric humidity with respect to ice (UTH i ). Since the required brightness temperatures (channels 12 and 6, T 12 and T 6 ) are intercalibrated to different versions of the HIRS sensors (HIRS/2 and HIRS/4) it is necessary to convert the channel 6 brightness temperatures which are intercalibrated to HIRS/4 into equivalent brightness temperatures intercalibrated to HIRS/2, which is achieved using a linear regression. Using the new regression coefficients we produce daily files of UTH i , T 12 and T 6 , for each NOAA satellite and METOP-A (Meteorological Operational Satellite Programme), which carry the HIRS instrument. From this we calculate daily and monthly means in 2.5 • × 2.5 • resolution for the northern midlatitude zone 30-60 • N. As a first application we calculate decadal means of UTH i and the brightness temperatures for the two decades 1980-1989 and 2000-2009. We find that the humidity mainly increased from the 1980s to the 2000s and that this increase is highly statistically significant in large regions of the considered midlatitude belt. The main reason for this result and its statistical significance is the corresponding increase of the T 12 variance. Changes of the mean brightness temperatures are less significant.

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“…This is coupled to a consistent radiative treatment of ice clouds, and an aerosol model that includes particle effects on liquid and ice clouds (Liu et al, 2012). Critical for contrail formation, CAM5 can simulate the mean relative humidity and reproduce the distribution of the frequency of ice supersaturation in the upper troposphere and lower stratosphere (UTLS) as observed from the Atmospheric Infrared Sounder (AIRS) satellite (Gettelman et al, 2006), including the hemispheric asymmetry of higher frequency of supersaturation at Southern Hemisphere midlatitudes.…”

Section: Model Descriptionmentioning

confidence: 99%

Simulated radiative forcing from contrails and contrail cirrus

Chen

Gettelman

2013

Atmos. Chem. Phys.

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Abstract.A comprehensive general circulation model including ice supersaturation is used to estimate the climate impact of aviation induced contrails. The model uses a realistic aviation emissions inventory for 2006 to initiate contrails, and allows them to evolve consistently with the model hydrologic cycle.The radiative forcing from linear contrails is very sensitive to the diurnal cycle. For linear contrails, including the diurnal cycle of air traffic reduces the estimated radiative forcing by 29 %, and for contrail cirrus estimates, the radiative forcing is reduced by 25 %. Estimated global radiative forcing from linear contrails is 0.0031 ± 0.0005 Wm −2 . The linear contrail radiative forcing is found to exhibit a strong diurnal cycle. The contrail cirrus radiative forcing is less sensitive to the diurnal cycle of flights. The estimated global radiative forcing from contrail cirrus is 0.013 ± 0.01 Wm −2 . Over regions with the highest air traffic, the regional effect can be as large as 1 Wm −2 .

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The Global Distribution of Supersaturation in the Upper Troposphere from the Atmospheric Infrared Sounder

Cited by 110 publications

References 36 publications

Balloon-borne match measurements of midlatitude cirrus clouds

Balloon-borne match measurements of midlatitude cirrus clouds

Technical Note: 30 years of HIRS data of upper tropospheric humidity

Simulated radiative forcing from contrails and contrail cirrus

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