High-Resolution Airborne Radar Observations of Mammatus

Mammatus are hanging lobes on the underside of clouds. Although many different mechanisms have been proposed for their formation, none have been rigorously tested. In this study, three-dimensional numerical simulations of mammatus on a portion of a cumulonimbus cirruslike anvil are performed to explore some of the dynamic and microphysical factors that affect mammatus formation and evolution. Initial conditions for the simulations are derived from observed thermodynamic soundings. Five observed soundings are chosen-four were associated with visually observed mammatus and one was not. Initial microphysical conditions in the simulations are consistent with in situ observations of cumulonimbus anvil and mammatus. Mammatus form in the four model simulations initialized with the soundings for which mammatus were observed, whereas mammatus do not form in the model simulation initialized with the no-mammatus sounding. Characteristics of the modeled mammatus compare favorably to previously published mammatus observations. Three hypothesized formation mechanisms for mammatus are tested: cloud-base detrainment instability, fallout of hydrometeors from cloud base, and sublimation of ice hydrometeors below cloud base. For the parameters considered, cloud-base detrainment instability is a necessary, but not sufficient, condition for mammatus formation. Mammatus can form without fallout, but not without sublimation. All the observed soundings for which mammatus were observed feature a dry-adiabatic subcloud layer of varying depth with low relative humidity, which supports the importance of sublimation to mammatus formation.

Section: Modification Of Soundings By Mammatussupporting

confidence: 93%

“…The presence of an inversion at the anvil base in Fig. 1b is consistent with some other soundings associated with mammatus (e.g., Clayton 1911;Hartmann 1920;Schneider 1920;Clarke 1962;Stith 1995;Winstead et al 2001;Schultz et al 2006).…”

Section: Observed Soundings Used To Initialize Modelsupporting

confidence: 89%

Numerical Simulation of Mammatus

Kanak

Straka

Schultz

2008

“…Respective maximum downdrafts are 21.8 and 1.9 m s 21 . These values are in the range of those seen in mammatus lobes by radar (Winstead et al 2001;Kollias et al 2005) and aircraft (Stith 1995), although observed updraft velocities are weaker. This difference can be explained by velocities in measurements applying only to the cloudy mammatus lobes themselves whereas model results apply more to the cloud-free regions that surround the descending mammatus lobes.…”

Section: Numerical Resultsmentioning

confidence: 52%

Mammatus Clouds as a Response to Cloud-Base Radiative Heating

Garrett

Schmidt

Kihlgren

et al. 2010

Mammatus clouds are the pouchlike lobes seen hanging from mid-to high-level clouds. They can look quite dramatic, but they are also interesting because they provide clues to what controls anvil cirrus dynamic evolution. Thus far, the most commonly accepted explanation for observed subsidence of mammatus lobes is that they are driven by evaporative cooling of precipitation, accelerated by mixing with dry subcloud air.Here, an alternative explanation is proposed: radiative temperature contrasts between cloud base and the lower troposphere destabilize cloudy air to create a rapidly deepening mixed layer, which creates positively buoyant intrusions of dry air into the cloud interior; mammatus lobes are just the descending branch of the resulting circulations. In this regard, mammatus cloud fields might be considered an upside-down analog to the radiatively driven formation of ''cloud holes'' seen at the tops of stratocumulus layers.

“…Mammatus clouds are among the more intriguing of atmospheric phenomena for their dramatic visual appearance, especially when the sun is low on the horizon and the contrast between pouches is at its highest and most colorful. Normally, mammatus lobes are smooth and regularly spaced, protruding downward from cloud base in visible and radar imagery (Martner 1995;Winstead et al 2001;Schultz et al 2006). Here we see mammatus-like structures that protrude instead upward from the cloud top.…”

Section: Discussion: Formation Mechanismsmentioning

confidence: 99%

Satellite Observations of an Unusual Cloud Formation near the Tropopause

Ferlay

Garrett

Minvielle

2014

This paper describes observations of a field of deep and regular cloud formations that spans several hundreds of kilometers at the top of a midlatitude frontal system in the North Pacific storm track. Space-based imagery of the event from active and passive measurements reveals smooth, clearly defined cloud lobes approximately 10 km across and 2-4 km deep that resemble upside-down mammatus. These observations, together with theoretical arguments and prior modeling work, suggest that the lobes were part of a deepening turbulent mixed layer that formed as a consequence of strong cloud-top radiative cooling. Over the course of a day, the cloud-top formation evolved to leave behind a sheet of cumuliform cirrus that stretched hundreds of kilometers across. The potential is for such clouds to facilitate mixing across the tropopause, much as cloudtop cooling drives the entrainment of free-tropospheric air into stratocumulus-topped boundary layers.