scholarly journals Determination of Best Tropopause Definition for Convective Transport Studies

2018 ◽  
Vol 75 (10) ◽  
pp. 3433-3446 ◽  
Author(s):  
Emily M. Maddox ◽  
Gretchen L. Mullendore
Keyword(s):  
Mass Transport ◽  
Potential Vorticity ◽  
Deep Convection ◽  
Three Dimensional ◽  
Static Stability ◽  
Convective Transport ◽  
Lapse Rate ◽  
Tracer Concentration ◽  
Temperature Lapse Rate ◽  
Cloud Resolving Model

An idealized three-dimensional cloud-resolving model is used to investigate the sensitivity of cross-tropopause convective mass transport to tropopause definition. A simulation is conducted to encompass the growth and decay cycle of a supercell thunderstorm, with a focus on irreversible transport above the tropopause. Five previously published tropopause definitions are evaluated: World Meteorological Organization (WMO) temperature lapse rate, potential vorticity, static stability, vertical curvature of the Brunt–Väisälä frequency, and stratospheric tracer concentration. By analyzing the behavior of different definitions both during and after active convection, we are able to define “best” choices for tropopause definitions as those that return to states most closely matching the preconvective environment. Potential vorticity and stratospheric tracer concentration are shown to perform poorly when analyzing deep convection. The WMO thermal tropopause and static stability definitions are found to perform the best, providing similar tropopause placement and quantities of irreversible mass transport. This investigation highlights the challenges of defining a tropopause in the vicinity of deep convection and demonstrates the need to clearly communicate calculation methods and threshold choices in the literature.

scholarly journals Thermal structure of intense convective clouds derived from GPS radio occultations

2012 ◽  
Vol 12 (12) ◽  
pp. 5309-5318 ◽  
Author(s):  
R. Biondi ◽  
W. J. Randel ◽  
S.-P. Ho ◽  
T. Neubert ◽  
S. Syndergaard
Keyword(s):  
Thermal Structure ◽  
Deep Convection ◽  
Lapse Rate ◽  
Orthogonal Polarization ◽  
Cold Temperatures ◽  
Temperature Lapse Rate ◽  
Convective Systems ◽  
Convective Clouds ◽  
Strong Inversion ◽  
Cloud Tops

Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.

Using Radio Occultation to Detect Clouds in the Middle and Upper Troposphere

2021 ◽  
Author(s):  
Jeana Mascio ◽  
Stephen S. Leroy ◽  
Robert P. d’Entremont ◽  
Thomas Connor ◽  
E. Robert Kursinski
Keyword(s):  
Relative Humidity ◽  
High Performance ◽  
Radio Occultation ◽  
Three Dimensional ◽  
Roc Curves ◽  
Lapse Rate ◽  
Cloud Detection ◽  
Upper Troposphere ◽  
Temperature Lapse Rate ◽  
Direct Sensitivity

AbstractRadio occultation (RO) measurements have little direct sensitivity to clouds, but recent studies have shown that they may have an indirect sensitivity to thin, high clouds that are difficult to detect using conventional passive space-based cloud sensors. We implement two RO-based cloud detection (ROCD) algorithms for atmospheric layers in the middle and upper troposphere. The first algorithm is based on the methodology of a previous study, which explored signatures caused by upper tropospheric clouds in RO profiles according to retrieved relative humidity, temperature lapse rate, and gradients in log-refractivity (ROCD-P), and the second is based on inferred relative humidity alone (ROCD-M). In both, atmospheric layers are independently predicted as cloudy or clear based on observational data, including high performance RO retrievals. In a demonstration, we use data from 10 days spanning seven months in 2020 of FORMOSAT-7/COSMIC-2. We use the forecasts of NOAA GFS to aid in the retrieval of relative humidity. The prediction is validated with a cloud truth dataset created from the imagery of the GOES-16 Advanced Baseline Imager (ABI) satellite and the GFS three-dimensional analysis of cloud state conditions. Given these two algorithms for the presence or absence of clouds, confusion matrices and receiver operating characteristic (ROC) curves are used to analyze how well these algorithms perform. The ROCD-M algorithm has a balanced accuracy, which defines the quality of the classification test that considers both the sensitivity and specificity, greater than 70% for all altitudes between 6 and 10.25 km.

Two- and Three-Dimensional Cloud-Resolving Model Simulations of the Mesoscale Enhancement of Surface Heat Fluxes by Precipitating Deep Convection

2006 ◽  
Vol 19 (1) ◽  
pp. 139-149 ◽  
Author(s):  
Xiaoqing Wu ◽  
Stephen Guimond
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Deep Convection ◽  
Three Dimensional ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Total Flux ◽  
Surface Heat Fluxes ◽  
Cloud Resolving Model ◽  
2D And 3D

Abstract Two-dimensional (2D) and three-dimensional (3D) cloud-resolving model (CRM) simulations are conducted to quantify the enhancement of surface sensible and latent heat fluxes by tropical precipitating cloud systems for 20 days (10–30 December 1992) during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The mesoscale enhancement appears to be analogous across both 2D and 3D CRMs, with the enhancement for the sensible heat flux accounting for 17% of the total flux for each model and the enhancement for the latent heat flux representing 18% and 16% of the total flux for 2D and 3D CRMs, respectively. The convection-induced gustiness is mainly responsible for the enhancement observed in each model simulation. The parameterization schemes of the mesoscale enhancement by the gustiness in terms of convective updraft, downdraft, and precipitation, respectively, are examined using each version of the CRM. The scheme utilizing the precipitation was found to yield the most desirable estimations of the mean fluxes with the smallest rms error. The results together with previous findings from other studies suggest that the mesoscale enhancement of surface heat fluxes by the precipitating deep convection is a subgrid process apparent across various CRMs and is imperative to incorporate into general circulation models (GCMs) for improved climate simulation.

Transient Environmental Sensitivities of Explicitly Simulated Tropical Convection

2010 ◽  
Vol 67 (4) ◽  
pp. 923-940 ◽  
Author(s):  
Stefan N. Tulich ◽  
Brian E. Mapes
Keyword(s):  
Deep Convection ◽  
Three Dimensional ◽  
Convective Clouds ◽  
Model Response ◽  
Effective Inhibition ◽  
Cloud Resolving Model ◽  
Response Enhancement ◽  
Vertical Displacements ◽  
Nonlocal Part ◽  
Homogeneous Temperature

Abstract A three-dimensional cloud-resolving model, maintained in a statistically steady convecting state by tropics-like forcing, is subjected to sudden (10 min) stimuli consisting of horizontally homogeneous temperature and/or moisture sources with various profiles. Ensembles of simulations are used to increase the statistical robustness of the results and to assess the deterministic nature of the model response for domain sizes near contemporary global model resolution. The response to middle- and upper-tropospheric perturbations is predominantly local in the vertical: convection damps the imposed stimulus over a few hours. Low-level perturbations are similarly damped, but also produce a vertically nonlocal response: enhancement or suppression of new deep convective clouds extending above the perturbed level. Experiments show that the “effective inhibition layer” for deep convection is about 4 km deep, far deeper than traditional convective inhibition defined for undilute lifted parcels. Both the local and nonlocal responses are remarkably linear but can be highly stochastic, especially if deep convection is only intermittently present (small domains, weak forcing). Quantitatively, temperature-versus-moisture perturbations in a ratio corresponding to adiabatic vertical displacements produce responses of roughly equal magnitude. However, moisture perturbations seem to provoke the nonlocal (upward spreading) type of response more effectively. This nonlocal part of the response is also more effective when background forcing intensity is weak. Only at very high intensity does the response approach the limits of purely local damping and pure determinism that would be most convenient for theory and parameterization.

The piecewise constant symmetric potential vorticity vortex in geophysical flows

2008 ◽  
Vol 614 ◽  
pp. 145-172 ◽  
Author(s):  
ÁLVARO VIÚDEZ
Keyword(s):  
Potential Vorticity ◽  
Three Dimensional ◽  
Static Stability ◽  
Geophysical Flows ◽  
Radial Dependence ◽  
Radial Solutions ◽  
Finite Radius ◽  
Piecewise Constant ◽  
Order Of Magnitude ◽  
Horizontal Cylinders

The concept of piecewise constant symmetric vortex in the context of three-dimensional baroclinic balanced geophysical flows is explored. The pressure gradients generated by horizontal cylinders and spherical balls of uniform potential vorticity (PV), or uniform material invariants, are obtained either analytically or numerically, in the general case of Boussinesq and f-plane dynamics as well as under the quasi-geostrophic and semigeostrophic dynamical approximations. Based on the order of magnitude of the different terms in the PV inversion equation, approximated PV equations are deduced. In some of these cases, radial solutions are possible and the interior and exterior solutions are found analytically. In the case of non-radial dependence, exterior solutions can be found numerically. Linear, and upper and lower bound approximations to the full PV inversion equations, and their respective solutions, are also included. However, the general solution for the pressure gradient in the vortex exterior does not have spherical symmetry and remains as an important theoretical challenge. It is suggested that, in order to maintain everywhere the inertial and static stability of the balanced geophysical flows, small balls of finite radius, rather than PV singularities, could become, specially in numerical applications, useful mathematical objects.

scholarly journals Thermal structure of intense convective clouds derived from GPS radio occultations

2011 ◽  
Vol 11 (10) ◽  
pp. 29093-29116 ◽  
Author(s):  
R. Biondi ◽  
W. J. Randel ◽  
S.-P. Ho ◽  
T. Neubert ◽  
S. Syndergaard
Keyword(s):  
Thermal Structure ◽  
Deep Convection ◽  
Lapse Rate ◽  
Orthogonal Polarization ◽  
Cold Temperatures ◽  
Temperature Lapse Rate ◽  
Convective Systems ◽  
Convective Clouds ◽  
Strong Inversion ◽  
Cloud Tops

Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.

scholarly journals Thermal Chains and Entrainment in Cumulus Updrafts. Part II: Analysis of Idealized Simulations

2020 ◽  
Vol 77 (11) ◽  
pp. 3661-3681 ◽  
Author(s):  
John M. Peters ◽  
Hugh Morrison ◽  
Adam C. Varble ◽  
Walter M. Hannah ◽  
Scott E. Giangrande
Keyword(s):  
Vertical Velocity ◽  
Conceptual Models ◽  
Deep Convection ◽  
Three Dimensional ◽  
Entrainment Rate ◽  
Vertical Profiles ◽  
Passive Tracer ◽  
Tracer Concentration ◽  
Environmental Relative Humidity

AbstractResearch has suggested that the structure of deep convection often consists of a series of rising thermals, or “thermal chain,” which contrasts with existing conceptual models that are used to construct cumulus parameterizations. Simplified theoretical expressions for updraft properties obtained in Part I of this study are used to develop a hypothesis explaining why this structure occurs. In this hypothesis, cumulus updraft structure is strongly influenced by organized entrainment below the updraft’s vertical velocity maximum. In a dry environment, this enhanced entrainment can locally reduce condensation rates and increase evaporation, thus eroding buoyancy. For moderate-to-large initial cloud radius R, this breaks up the updraft into a succession of discrete pulses of rising motion (i.e., a thermal chain). For small R, this leads to the structure of a single, isolated rising thermal. In contrast, moist environments are hypothesized to favor plume-like updrafts for moderate-to-large R. In a series of axisymmetric numerical cloud simulations, R and environmental relative humidity (RH) are systematically varied to test this hypothesis. Vertical profiles of fractional entrainment rate, passive tracer concentration, buoyancy, and vertical velocity from these runs agree well with vertical profiles calculated from the theoretical expressions in Part I. Analysis of the simulations supports the hypothesized dependency of updraft structure on R and RH, that is, whether it consists of an isolated thermal, a thermal chain, or a plume, and the role of organized entrainment in driving this dependency. Additional three-dimensional (3D) turbulent cloud simulations are analyzed, and the behavior of these 3D runs is qualitatively consistent with the theoretical expressions and axisymmetric simulations.

Towards an Understanding of the Structure of Jupiter’s Atmosphere using the Ammonia Distribution and the Transformed Eulerian Mean Theory

2021 ◽  
Author(s):  
Sukyoung Lee ◽  
Yohai Kaspi
Keyword(s):  
Vertical Velocity ◽  
Static Stability ◽  
Hadley Cell ◽  
Lapse Rate ◽  
Scaling Analysis ◽  
Overturning Circulation ◽  
Temperature Lapse Rate ◽  
Ferrel Cell ◽  
The Tropics ◽  
Transformed Eulerian Mean

AbstractThe structure and stability of Jupiter’s atmosphere is analyzed using transformed Eulerian mean (TEM) theory. Utilizing the ammonia distribution derived from microwave radiometer measurements of the Juno orbiter, the latitudinal and vertical distribution of the vertical velocity in the interior of Jupiter’s atmosphere is inferred. The resulting overturning circulation is then interpreted in the TEM framework to offer speculation of the vertical and meridional temperature distribution. In the extratropics, the analyzed vertical velocity field shows Ferrel-cell-like patterns associated with each of the jets. A scaling analysis of the TEM overturning circulation equation suggests that in order for the Ferrel-cell-like patterns to be visible in the ammonia distribution, the static stability of Jupiter’s weather layer should be on the order of 1 × 10−2 s−1. In the tropics, the ammonia distribution suggests strong upward motion which is reminiscent of the rising branch of the Hadley cell where the static stability is weaker. Taken together, the analysis suggests that the temperature lapse rate in the extratropics is markedly greater than that in the tropics. Because the cloud top temperature is nearly uniform across all latitudes, the analysis suggests that in the interior of the weather layer, there could exist a temperature gradient between the tropical and extratropical regions.

scholarly journals A model study on the influence of overshooting convection on TTL water vapour

2010 ◽  
Vol 10 (20) ◽  
pp. 9833-9849 ◽  
Author(s):  
M. E. E. Hassim ◽  
T. P. Lane
Keyword(s):  
Water Vapour ◽  
Deep Convection ◽  
Three Dimensional ◽  
Direct Role ◽  
Water Vapour Content ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Model Study ◽  
Cloud Resolving Model ◽  
Passive Tracers

Abstract. Overshooting deep convection that penetrates into the Tropical Tropopause Layer (TTL) is thought to have an important role in regulating the water vapour content of this region. Yet, the net effect of such convection and the dominant mechanisms remain unclear. This study uses two idealised three-dimensional cloud-resolving model simulations to examine the influence of overshooting convection on water vapour when it penetrates into two different TTL environments, one supersaturated and the other subsaturated with respect to ice. These simulations show that the overshooting convection plays a direct role in driving the ambient environment towards ice saturation through either net moistening (subsaturated TTL) or net dehydration (supersaturated TTL). Moreover, in these cases the extent of dehydration in supersaturated conditions is greater than the moistening in subsaturated conditions. With the aid of modelled passive tracers, the relative roles of transport, mixing and ice microphysics are assessed; ultimately, ice sublimation and scavenging processes play the most important role in defining the different TTL relative humidity tendencies. In addition, significant moistening in both cases is modelled well into the subsaturated tropical lower stratosphere (up to 450 K), even though the overshooting turrets only reach approximately 420 K. It is shown that this moistening is the result of jumping cirrus, which is induced by the localised upward transport and mixing of TTL air following the collapse of the overshooting turret.

scholarly journals Invigoration and Capping of a Convective Rainband ahead of a Potential Vorticity Anomaly

2017 ◽  
Vol 145 (6) ◽  
pp. 2093-2117 ◽  
Author(s):  
Geraint Vaughan ◽  
Bogdan Antonescu ◽  
David M. Schultz ◽  
Christopher Dearden
Keyword(s):  
Potential Vorticity ◽  
Dominant Role ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Static Stability ◽  
Causal Link ◽  
Minor Role ◽  
Low Level ◽  
Upper Level ◽  
A Minor

Abstract Deep convection frequently occurs on the eastern side of upper-level troughs, or potential vorticity (PV) anomalies. This is consistent with uplift ahead of a cyclonic PV anomaly, and consequent reduction in static stability and increase of convective available potential energy (CAPE). Nevertheless, the causal link between upper-level PV and deep convection has not been proven, and given that lift, moisture, and instability must all be present for deep convection to occur it is not clear that upper-level forcing is sufficient. In this paper a convective rainband that intensified ahead of a cyclonic PV anomaly in an environment with little CAPE (~10 J kg−1) is examined to determine the factors responsible for its intensification. The key feature was a low-level convergence line, arising from the remnants of an occluded front embedded in the low-level cyclonic flow. The rainband’s intensity and morphology was influenced by the remnants of a tropopause fold that capped convection at midlevels in the southern part of the band, and by a reduction in upper-level static stability in the northern part of the band that allowed the convection to reach the tropopause. Ascent ahead of the trough appears to have played only a minor role in conditioning the atmosphere to convection: in most cases the ascending airstream had previously descended in the flow west of the trough axis. Thus, simple “PV thinking” is not capable of describing the development of the rainband, and it is concluded that preexisting low-level wind and humidity features played the dominant role.

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