HIRDLS and CALIPSO observations of tropical cirrus

Massie, Steven T.; Gille, J. C.; Craig, Cheryl; Khosravi, R.; Barnett, J. J.; Read, W. G.; Winker, David M.

doi:10.1029/2009jd012100

Cited by 59 publications

(74 citation statements)

References 28 publications

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“…Because the default soundings in previous SOWER campaigns did not include any sensors for particles, we could not estimate the total water content in which the air mass has ice particles. In addition, for the campaign region and period (i.e., over the western Pacific in the boreal winter), cirrus clouds are common in the TTL; Shibata et al, 2007;Fujiwara et al, 2009;Massie et al, 2010;Yang et al, 2010;Inai et al, 2012;Shibata et al, 2012). If we could observe ice particles and measure their concentration and size distribution, we could estimate their growth rate under the assumption that a critical relative humidity leads to the initiation of ice nucleation, using the same technique as that employed to estimate the efficiency of dehydration (Sect.…”

Section: Lack Of Dehydrated Cases Near the Cold Pointmentioning

confidence: 99%

Dehydration in the tropical tropopause layer estimated from the water vapor match

et al. 2013

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We apply the match technique, whereby the same air mass is observed more than once and such cases are termed a "match", to study the dehydration process associated with horizontal advection in the tropical tropopause layer (TTL) over the western Pacific. The matches are obtained from profile data taken by the Soundings of Ozone and Water in the Equatorial Region (SOWER) campaign network observations using isentropic trajectories calculated from European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. For the matches identified, extensive screening procedures are performed to verify the representativeness of the air parcel and the validity of the isentropic treatment, and to check for possible water injection by deep convection, consistency between the sonde data and analysis field referring to the ozone conservation. Among the matches that passed the screening tests, we identified some cases corresponding to the first quantitative value of dehydration associated with horizontal advection in the TTL. The statistical features of dehydration for the air parcels advected in the lower TTL are derived from the matches. The threshold of nucleation is estimated to be 146 ± 1% (1σ) in relative humidity with respect to ice (RH_ice), while dehydration seems to continue until RH_ice reaches about 75 ± 23% (1σ) in the altitude region from 350 to 360 K. The efficiency of dehydration expressed by the relaxation time required for the supersaturated air parcel to approach saturation is empirically determined from the matches. A relaxation time of approximately one hour reproduces the second water vapor observation reasonably well, given the first observed water vapor amount and the history of the saturation mixing ratio during advection in the lower TTL

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Section: Lack Of Dehydrated Cases Near the Cold Pointmentioning

confidence: 99%

Dehydration in the tropical tropopause layer estimated from the water vapor match

et al. 2013

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“…We analyzed SVC during the boreal summer (JJA) and winter (DJF), the two periods with the largest tropical cirrus cover (Massie et al, 2010 (Fig. 2, row 1) with maximum occurrence around 195 K, and are on average 5 K warmer in JJA.…”

Section: Svc Observations From Caliopmentioning

confidence: 99%

On the origin of subvisible cirrus clouds in the tropical upper troposphere

et al. 2012

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Abstract. Spaceborne lidar observations have recently revealed a previously undetected significant population of Subvisible Cirrus (SVC). We show them to be colder than −74 • , with an optical depth below 0.0015 on average. The formation and persistence over time of this new cloud population could be related to several atmospheric phenomena. In this paper, we investigate if these clouds follow the same formation mechanisms as the general tropical cirrus population (including convection and in-situ ice nucleation), or if specific nucleation sites and trace species play a role in their formation. The importance of three scenarios in the formation of the global SVC population is investigated through different approaches that include comparisons with data imaging from several spaceborne instruments and back-trajectories that document the history and behavior of air masses leading to the point in time and space where subvisible cirrus were detected. In order to simplify the study of their formation, we singled out SVC with coherent temperature histories (mean variance lower than 4 K) according to back-trajectories along 5, 10 or 15 days (respectively 58, 25 and 11 % of SVC). Our results suggest that external processes, including local increases in liquid and hygroscopic aerosol concentration (either through biomass burning or volcanic injection forming sulfate-based aerosols in the troposphere or the stratosphere) have very limited short-term or mid-term impact on the SVC population. On the other hand, we find that ∼ 20 % of air masses leading to SVC formation interacted with convective activity 5 days before they led to cloud formation and detection, a number that climbs to 60 % over 15 days. SVC formation appears especially linked to convection over Africa and Central America, more so during JJA than DJF. These results support the view that the SVC population observed by CALIOP is an extension of the general upper tropospheric ice clouds population with its extreme thinness as its only differentiating factor.

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“…For example, satellite observations indicate that thin cirrus are present in the tropical uppermost troposphere over the western Pacific during Boreal winter about 50-80% of the time (Wang et al, 1996;Yang et al, 2009;Massie et al, 2009). Cirrus in this region of the atmosphere are important for a number of reasons.…”

Section: Introductionmentioning

confidence: 99%

Ice nucleation and cloud microphysical properties in tropical tropopause layer cirrus

et al. 2010

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Abstract.In past modeling studies, it has generally been assumed that the predominant mechanism for nucleation of ice in the uppermost troposphere is homogeneous freezing of aqueous aerosols. However, recent in situ and remotesensing measurements of the properties of cirrus clouds at very low temperatures in the tropical tropopause layer (TTL) are broadly inconsistent with theoretial predictions based on the homogeneous freezing assumption. The nearly ubiquitous occurence of gravity waves in the TTL makes the predictions from homogeneous nucleation theory particularly difficult to reconcile with measurements. These measured properties include ice number concentrations, which are much lower than theory predicts; ice crystal size distributions, which are much broader than theory predicts; and cloud extinctions, which are much lower than theory predicts. Although other explanations are possible, one way to limit ice concentrations is to have on the order of 50 L −1 effective ice nuclei (IN) that could nucleate ice at relatively low supersaturations. We suggest that ammonium sulfate particles, which would be dry much of the time in the cold TTL, are a potential IN candidate for TTL cirrus. However, this mechanism remains to be fully quantified for the size distribution of ammonium sulfate (possibly internally mixed with organics) actually present in the upper troposphere. Possible implications of the observed cloud microphysical properties for ice sedimentation, dehydration, and cloud persistence are also discussed.

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HIRDLS and CALIPSO observations of tropical cirrus

Cited by 59 publications

References 28 publications

Dehydration in the tropical tropopause layer estimated from the water vapor match

Dehydration in the tropical tropopause layer estimated from the water vapor match

On the origin of subvisible cirrus clouds in the tropical upper troposphere

Ice nucleation and cloud microphysical properties in tropical tropopause layer cirrus

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