Deep convective cross-tropopause transport in the tropics and evidence by A-Train satellites (original) (raw)
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Recent evidences of deep convective transport through the tropopause
A few years ago, we identified a deep convective transport mechanism (storm top gravity wave breaking) of water vapor through the tropopause so that tropospheric water substance can be injected into the lower stratosphere via this pathway. The main evidence we presented previously was taken from the lower resolution geostationary and a few polar orbiting satellite images of the storm anvil top cirrus plumes. Recent observations turn out more supporting evidences for this important vertical 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 unseen by lower resolution GOES images. Furthermore, movies taken by a building top webcam also demonstrate that the jumping cirrus phenomenon, first identified by T. Fujita in 1980s, is quite common in active thunderstorm cells, quite contrary to previous belief that it is a rare occurrence. We have used a c...
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.
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.
Water Vapor, Clouds, and Saturation in the Tropical Tropopause Layer
J. Geophys. Res., 2019
The goal of this investigation is to understand the mechanism behind the observed high relative humidity with respect to ice (RHi) in the tropical region between~14 km (150 hPa) and the tropopause, often referred to as the tropical tropopause layer (TTL). As shown by satellite, aircraft, and balloon observations, high (>80%) RHi regions are widespread within the TTL. Regions with the highest RHi are colocated with extensive cirrus. During boreal winter, the TTL RHi is highest over the Tropical Western Pacific (TWP) with a weaker maximum over South America and Africa. In the winter, TTL temperatures are coldest and upward motion is the greatest in the TWP. It is this upward motion, driving humid air into the colder upper troposphere that produces the persistent high RHi and cirrus formation. Back trajectory calculations show that comparable adiabatic and diabatic processes contribute to this upward motion. We construct a bulk model of TWP TTL water vapor transport that includes cloud nucleation and ice microphysics that quantifies how upward motion drives the persistent high RHi in the TTL region. We find that atmospheric waves triggering cloud formation regulate the RHi and that convection dehydrates the TTL. Our forward domain-filling trajectory model is used to more precisely simulate the TTL spatial and vertical distribution of RHi. The observed RHi distribution is reproduced by the model, and we show that convection increases RHi below the base of the TTL with little impact on the RHi in the TTL region. Plain Language Summary Satellite, aircraft, and balloon observations show that the upper tropical tropospheric humidity is close to saturation. This high humidity is the result of the near-continuous upward movement of water vapor from the midtroposphere into the colder upper troposphere that results in extensive cirrus formation. Bulk and trajectory model simulations show how this process works and that convective injection of water into the tropical upper troposphere is relatively unimportant.
The factors that control the influence of deep convective detrainment on water vapor in the tropical upper troposphere are examined using observations from multiple satellites in conjunction with a trajectory model. Deep convection is confirmed to act primarily as a moisture source to the upper troposphere, modulated by the ambient relative humidity (RH). Convective detrainment provides strong moistening at low RH and offsets drying due to subsidence across a wide range of RH. Strong day-to-day moistening and drying takes place most frequently in relatively dry transition zones, where between 0.01% and 0.1% of Tropical Rainfall Measuring Mission Precipitation Radar observations indicate active convection. Many of these strong moistening events in the tropics can be directly attributed to detrainment from recent tropical convection, while others in the subtropics appear to be related to stratosphere-troposphere exchange. The temporal and spatial limits of the convective source are estimated to be about 36-48 h and 600-1500 km, respectively, consistent with the lifetimes of detrainment cirrus clouds. Larger amounts of detrained ice are associated with enhanced upper tropospheric moistening in both absolute and relative terms. In particular, an increase in ice water content of approximately 400% corresponds to a 10-90% increase in the likelihood of moistening and a 30-50% increase in the magnitude of moistening.
Aircraft observations of thin cirrus clouds near the tropical tropopause
Journal of Geophysical Research: Atmospheres, 2001
This work describes aircraft-based lidar observations of thin cirrus clouds at the tropical tropopause in the central Pacific obtained during the Tropical Ozone Transport Experiment/Vortex Ozone Transport Experiment (TOTE/VOTE) in December 1995 and February 1996. Thin cirrus clouds were found at the tropopause on each of the four flights which penetrated within 15 degrees of the equator at 200-210 east longitude. The altitudes of these clouds exceeded 18 km at times. The cirrus
The impact of subvisible cirrus clouds near the tropical tropopause on stratospheric water vapor
Geophysical Research Letters, 1998
The radiative impact of subvisible cirrus ice clouds at and just below the tropical tropopause has been studied using a zonally averaged interactive chemistryradiation-dynamics model. Model runs have been performed with and without the inclusion of the radiative heating of these thin ice clouds, and with and without sedimentation. Near-infrared optical depths of 0.005-0.08 were computed for assumed log-normal size distributions of spherical particles having mode radii of 2-10 pm. Particles with 6 pm mode radii have computed scattering ratios of 3-15 at 603 nm, in good agreement with lidar observations. The increased radiative heating of these clouds, 0.1-0.2 K/day, results in temperature increases of 1-2 K and vertical velocity increases of 0.02-0.04 mm/s. As a consequence of the warmer tropopause, lower stratosphere water vapor increases by as much as i ppmv. The dehydration resulting from sedimentation was found to be a much smaller effect.
A case study of formation and maintenance of a lower stratospheric cirrus cloud over the tropics
A rare occurrence of stratospheric cirrus at 18.6 km height persisting for about 5 days during 3-7 March 2014 is inferred from the ground-based Mie lidar observations over Gadanki (13.5 • N, 79.2 • E) and spaceborne observations. Due to the vertical transport by large updrafts on 3 March in the troposphere, triggered by a potential vorticity intrusion, the water vapour mixing ratio shows an increase around the height of 18.6 km. Relative humidity with respect to ice is ∼ 150 %, indicating that the cirrus cloud may be formed though homogeneous nucleation of sulfuric acid. The cirrus cloud persists due to the cold anomaly associated with the presence of a 4-day wave.