Effect of an extratropical mesoscale convective system on water vapor transport in the upper troposphere/lower stratosphere: A modeling study (original) (raw)
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Cross Tropopause Transport of Water by Mid-Latitude Deep Convective Storms: A Review
Terrestrial, Atmospheric and Oceanic Sciences, 2011
Recent observational and numerical modeling studies of the mechanisms which transport moisture to the stratosphere by deep convective storms at mid-latitudes are reviewed. Observational evidence of the cross-tropopause transport of moisture by thunderstorms includes satellite, aircraft and ground-based data. The primary satellite evidence is taken from both conventional satellite of thunderstorm images and CloudSat vertical cloud cross-section images. The conventional satellite images show cirrus plumes above the anvil tops of some of the convective storms where the anvils are already at the tropopause level. The CloudSat image shows an indication of penetration of cirrus plume into the stratosphere. The aircraft observations consist of earlier observations of the "jumping cirrus" phenomenon reported by Fujita and recent detection of ice particles in the stratospheric air associated with deep convective storms. The ground-based observations are video camera records of the jumping cirrus phenomenon occurring at the top of thunderstorm cells. Numerical model studies of the penetrative deep convective storms were performed utilizing a three-dimensional cloud dynamical model to simulate a typical severe storm which occurred in the US Midwest region on 2 August 1981. Model results indicate two physical mechanisms that cause water to be injected into the stratosphere from the storm: (1) the jumping cirrus mechanism which is caused by the gravity wave breaking at the cloud top, and (2) an instability caused by turbulent mixing in the outer shell of the overshooting dome. Implications of the penetrative convection on global processes and a brief future outlook are discussed.
Transport of water vapor in the tropical tropopause layer
Geophysical Research Letters, 2002
1] A trajectory model coupled to a simple micro-physical model is used to explore the observed relationship between convection, water vapor and cirrus clouds in the tropical tropopause layer (TTL). Horizontal transport associated with the local Hadley circulation leads to water vapor minima in the winter hemisphere separated from the convective regions and the region of minimum temperatures. These spatial signatures are consistent with observations of water vapor and cirrus in the TTL from the Halogen Occultation Experiment (HALOE). In the simulations, one third of observed ice is formed due to horizontal transport through cold regions. Applied variations in temperature over time scales longer than a few hours, similar to gravity wave induced perturbations, act to lower the simulated water vapor.
Convective Hydration of the Upper Troposphere and Lower Stratosphere
Journal of Geophysical Research: Atmospheres, 2018
We use our forward domain filling trajectory model to explore the impact of tropical convection on stratospheric water vapor (H 2 O) and tropical tropopause layer cloud fraction (TTLCF). Our model results are compared to winter 2008/2009 TTLCF derived from Cloud-Aerosol Lidar with Orthogonal Polarization and lower stratospheric H 2 O observations from the Microwave Limb Sounder. Convection alters the in situ water vapor by driving the air toward ice saturation relative humidity. If the air is subsaturated, then convection hydrates the air through the evaporation of ice, but if the air is supersaturated, then convective ice crystals grow and precipitate, dehydrating the air. On average, there are a large number of both hydrating and dehydrating convective events in the upper troposphere, but hydrating events exceed dehydrating events. Explicitly adding convection produces a less than 2% increase in global stratospheric water vapor during the period analyzed here. Tropical tropopause temperature is the primary control of stratospheric water vapor, and unless convection extends above the tropopause, it has little direct impact. Less than 1% of the model parcels encounter convection above the analyzed cold-point tropopause. Convection, on the other hand, has a large impact on TTLCF. The model TTLCF doubles when convection is included, and this sensitivity has implications for the future climate-related changes, given that tropical convective frequency and convective altitudes may change. Plain Language Summary Deep convection has been invoked as a significant source for stratospheric water vapor based on aircraft observations. This modelling study shows that deep convection plays almost no role in directly hydrating the stratosphere because deep convection rarely penetrates the tropopause 'cold trap' that largely controls stratospheric water vapor.
ATMOSPHERIC CHEMISTRY AND PHYSICS
The aim of this paper is to study the impacts of overshooting convection at a local scale on the water distribution in the tropical UTLS. Overshooting convection is assumed to be one of the processes controlling the entry of water vapour mixing ratio in the stratosphere by injecting ice crystals above the tropopause which later sublimate and hydrate the lower stratosphere. For this purpose, we quantify the individual impact of two cases of overshooting convection in Africa observed during SCOUT-AMMA: the case of 4 August 2006 over Southern Chad which is likely to have influenced the water vapour measurements by micro-SDLA and FLASH-B from Niamey on 5 August, and the case of a mesoscale convective system over Aïr on 5 August 2006. We make use of high resolution (down to 1 km horizontally) nested grid simulations with the three-dimensional regional atmospheric model BRAMS (Brazilian Regional Atmospheric Modelling System). In both cases, BRAMS succeeds in simulating the main features o...
Further evidences of deep convective vertical transport of water vapor through the tropopause
Atmospheric Research, 2009
A few years ago, we identified a deep convective transport mechanism, of water vapor through the tropopause, namely, storm top gravity wave breaking, such that tropospheric water substance can be injected into the lower stratosphere via this pathway. The main evidence presented previously was taken from the lower resolution AVHRR images of the storm anvil top cirrus plumes obtained by polar orbiting satellites. Recent observations have provided further supporting evidence for this important cross-tropopause transport mechanism. There are now many higher resolution satellite images, mainly from MODIS instrument, that show more definitely the existence of these plumes, many of which would probably be unseen by lower resolution images. Furthermore, a thunderstorm movie taken in Denver (USA) area during STEPS2000 field campaign and another thunderstorm movie taken by a building top webcam in Zurich also demonstrate that the jumping cirrus phenomenon, first identified by T. Fujita in 1980s, may be quite common in active thunderstorm cells, quite contrary to previous belief that it is rare. We have used a cloud model to demonstrate that the jumping cirrus is exactly the gravity wave breaking phenomenon that transports water vapor through the tropopause. These additional evidences provide increasing support that deep convection contributes substantially to the troposphere-to-stratosphere transport of water substance. This corroborates well with recent studies of the stratospheric HDO/H 2 O ratio which is much highly than it would be if the transport is via slow ascent. The only explanation that can be used to interpret this observation at present is that water substance is transported through the tropopause via rapid vertical motion, i.e., deep convection.
Quarterly Journal of the Royal Meteorological Society, 1999
Stratospheric humidity analyses produced operationally by the European Centre for Medium-Range Weather Forecasts (ECMWF) are discussed for the period since late January 1996 when the practice of resetting the upperlevel specific humidity to a fixed value at each analysis time was abandoned. Near-tropopause analyses are in reasonable overall agreement with independent observations. Very low humidities occur in conjunction with deep convection and a particularly cold tropopause over the equatorial western Pacific during the northern winter. Drying occurs also in the cold core of the Antarctic polar-night vortex. The lower stratosphere is moistened in the outer tropics and subtropics in summer and autumn, predominantly in the northern hemisphere. Changes associated with the latest occurrence of El Niiio are illustrated.