In situ measurements of tropical cloud properties in the West African Monsoon: upper tropospheric ice clouds, Mesoscale Convective System outflow, and subvisual cirrus

Frey, W.; Borrmann, Stephan; Kunkel, Daniel; Weigel, Ralf; Reus, M. de; Schläger, Hans; Roiger, Anke; Voigt, Christiane; Hoor, Peter; Curtius, Joachim; Krämer, M.; Schiller, C.; Volk, C. M.; Homan, C. D.; Fierli, F.; Donfrancesco, G. Di; Ulanovsky, A.; Ravegnani, F.; Sitnikov, N.; Viciani, Silvia; D’Amato, Francesco; Shur, G. N.; Belyaev, G. V.; Law, Kathy S.; Cairo, F.

doi:10.5194/acp-11-5569-2011

Cited by 67 publications

(93 citation statements)

References 89 publications

(135 reference statements)

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“…However, we find that large supersaturations can persist in the low ice concentration cirrus. The ATTREX measurements, as well as measurements from several previous high-altitude aircraft campaigns, indicate that these low-concentration cirrus are prevalent throughout the TTL (11)(12)(13)(14)(15)(16). The high ice concentration cirrus reported here seem to occur much less frequently.…”

Section: Resultssupporting

confidence: 45%

See 1 more Smart Citation

Ice nucleation and dehydration in the Tropical Tropopause Layer

Jensen

Diskin

Lawson

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

135

174

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Optically thin cirrus near the tropical tropopause regulate the humidity of air entering the stratosphere, which in turn has a strong influence on the Earth's radiation budget and climate. Recent highaltitude, unmanned aircraft measurements provide evidence for two distinct classes of cirrus formed in the tropical tropopause region: (i) vertically extensive cirrus with low ice number concentrations, low extinctions, and large supersaturations (up to ∼70%) with respect to ice; and (ii) vertically thin cirrus layers with much higher ice concentrations that effectively deplete the vapor in excess of saturation. The persistent supersaturation in the former class of cirrus is consistent with the long time-scales (several hours or longer) for quenching of vapor in excess of saturation given the low ice concentrations and cold tropical tropopause temperatures. The low-concentration clouds are likely formed on a background population of insoluble particles with concentrations less than 100 L −1 (often less than 20 L −1 ), whereas the high ice concentration layers (with concentrations up to 10,000 L −1 ) can only be produced by homogeneous freezing of an abundant population of aqueous aerosols. These measurements, along with past high-altitude aircraft measurements, indicate that the low-concentration cirrus occur frequently in the tropical tropopause region, whereas the high-concentration cirrus occur infrequently. The predominance of the low-concentration clouds means cirrus near the tropical tropopause may typically allow entry of air into the stratosphere with as much as ∼1.7 times the ice saturation mixing ratio. ATTREX | ice nucleiA lthough the stratosphere is extremely dry compared with the troposphere, stratospheric humidity plays crucial roles in both atmospheric chemistry and climate. As the primary source of hydroxyl (OH) radicals, H 2 O plays an important role in the regulation of stratospheric ozone. Small changes in stratospheric humidity can have significant influence on the Earth's radiation budget and climate (1, 2). Model simulations show that increases in stratospheric humidity enhance the rate of ozone destruction, cool the lower stratosphere, and warm the surface (3, 4).Air enters the stratospheric overworld (above 380 K potential temperature) almost exclusively via ascent across the tropical tropopause. This fact has motivated interest in understanding processes occurring in the transition layer between the tropical troposphere and stratosphere, a region of the atmosphere referred to as the Tropical Tropopause Layer (TTL). Physical processes occurring in this layer set the boundary condition for the composition and humidity of the stratosphere. It is well established that the aridity of the stratosphere is associated with "freeze-drying" of air as it passes through the cold TTL (5, 6). Deposition growth of ice crystals in optically thin, laminar TTL cirrus depletes vapor in excess of saturation, and the ice crystals sediment relative to the slowly ascending air. The common occurrence of these thin, ...

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Section: Resultssupporting

confidence: 45%

“…High-altitude aircraft sampling in various tropical locations indicated ice concentrations almost exclusively less than 100 L −1 (11)(12)(13)(14)(15)(16). This result is in conflict with theoretical expectations.…”

Section: Attrex | Ice Nucleimentioning

confidence: 64%

Ice nucleation and dehydration in the Tropical Tropopause Layer

Jensen

Diskin

Lawson

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

135

174

View full text Add to dashboard Cite

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“…The analysis also shows a single mode structure centered on diameters in the range of 11 to 14μm with a maximum concentration of 385 cm -3 (Fig.6). The recorded values of the concentration number are consistent by those reported in the literature for a maritime cumulus clouds (Hobbs et al 1980, Hobbs & Rangno 1985. The derived mean volume diameter MVD of cloud particles oscillated during the various passes between 10 and 11.5μm with a minimum of 9.3μm and a peak of 12.7μm.…”

Section: Evolution Of Cloud Microphysical Parameterssupporting

confidence: 89%

Microphysical characteristics of cumulus clouds as observed in some African countries

Merrouchi¹

2014

IJAG

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This paper analyses airborne measurements of several midlevel and mixed-phase cumulus clouds observed in different environments (maritime, continental, shallow and deep convection) obtained during the scientific experiments performed by national weather modification programs in Morocco and Burkina Faso. Three cases are documented in this paper presenting the synoptic meteorological situation leading to the formation and the development of the sampled clouds and the results of the measurements collected using instrumental aircrafts. Several passes were made at the top of the sampled clouds and reported data were collected and analysed describing the variability of the measured parameters at various altitudes and thus different temperature values (negative and positive temperatures). The dependency of the liquid water content to the temperature has been studied but also its variation with regard to the vertical velocity and to the total concentration number of cloud particles. Keywords: Aircraft Measurements, Cloud Microphysics, Liquid Water Content, West African Monsoon.

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“…In these particular cases, the extinction coefficient ranges from 0.01 to 0.1 km −1 and the median radii are always smaller than or equal to 6 µm. These median radii are very small and can only be expected for sub-visible cirrus clouds (Iwasaki et al, 2007;Lawson et al, 2008;Davis et al, 2010;Frey et al, 2011 …”

Section: Ice Cloud Simulationsmentioning

confidence: 97%

Volcanic ash detection with infrared limb sounding: MIPAS observations and radiative transfer simulations

Grießbach¹,

Hoffmann²,

Spang³

et al. 2014

Atmos. Meas. Tech.

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Abstract. Small volcanic ash particles have long residence times in the troposphere and the stratosphere so that they have significant impact on the Earth's radiative budget and consequently affect climate. For global long-term observations of volcanic aerosol, infrared limb measurements provide excellent coverage, sensitivity to thin aerosol layers, and altitude information. The optical properties of volcanic ash and ice particles, derived from micro-physical properties, have opposing spectral gradients between 700 and 960 cm −1 for small particle sizes. Radiative transfer simulations that account for single scattering showed that the opposing spectral gradients directly transfer to infrared limb spectra. Indeed, we found the characteristic spectral signature, expected for volcanic ash, in measurements of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) after the eruption of the Chilean volcano Puyehue-Cordón Caulle in June 2011. From these measurements we derived an ash detection threshold function. The empirical ash detection threshold was confirmed in an extensive simulations study covering a wide range of atmospheric conditions, particle sizes and particle concentrations for ice, volcanic ash and sulfate aerosol. From the simulations we derived the upper detectable effective radius of 3.5 µm and the detectable extinction coefficient range of 5 × 10 −3 to 1 × 10 −1 km −1 . We also showed that this method is only sensitive to volcanic ash particles, but not to volcanic sulfate aerosol. This volcanic ash detection method for infrared limb measurements is a fast and reliable method and provides complementary information to existing satellite aerosol products.

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In situ measurements of tropical cloud properties in the West African Monsoon: upper tropospheric ice clouds, Mesoscale Convective System outflow, and subvisual cirrus

Cited by 67 publications

References 89 publications

Ice nucleation and dehydration in the Tropical Tropopause Layer

Ice nucleation and dehydration in the Tropical Tropopause Layer

Microphysical characteristics of cumulus clouds as observed in some African countries

Volcanic ash detection with infrared limb sounding: MIPAS observations and radiative transfer simulations

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