scholarly journals Isentropic Analysis of a Simulated Hurricane

2016 ◽  
Vol 73 (5) ◽  
pp. 1857-1870 ◽  
Author(s):  
Agnieszka A. Mrowiec ◽  
Olivier M. Pauluis ◽  
Fuqing Zhang
Keyword(s):  
Mass Transport ◽  
Potential Temperature ◽  
Wrf Model ◽  
Secondary Circulation ◽  
Equivalent Potential Temperature ◽  
Moist Convection ◽  
Shallow Convection ◽  
High Entropy ◽  
Equivalent Potential ◽  
Wide Range

Abstract Hurricanes, like many other atmospheric flows, are associated with turbulent motions over a wide range of scales. Here the authors adapt a new technique based on the isentropic analysis of convective motions to study the thermodynamic structure of the overturning circulation in hurricane simulations. This approach separates the vertical mass transport in terms of the equivalent potential temperature of air parcels. In doing so, one separates the rising air parcels at high entropy from the subsiding air at low entropy. This technique filters out oscillatory motions associated with gravity waves and separates convective overturning from the secondary circulation. This approach is applied here to study the flow of an idealized hurricane simulation with the Weather Research and Forecasting (WRF) Model. The isentropic circulation for a hurricane exhibits similar characteristics to that of moist convection, with a maximum mass transport near the surface associated with a shallow convection and entrainment. There are also important differences. For instance, ascent in the eyewall can be readily identified in the isentropic analysis as an upward mass flux of air with unusually high equivalent potential temperature. The isentropic circulation is further compared here to the Eulerian secondary circulation of the simulated hurricane to show that the mass transport in the isentropic circulation is much larger than the one in secondary circulation. This difference can be directly attributed to the mass transport by convection in the outer rainband and confirms that, even for a strongly organized flow like a hurricane, most of the atmospheric overturning is tied to the smaller scales.

The Global Atmospheric Circulation in Moist Isentropic Coordinates

2010 ◽  
Vol 23 (11) ◽  
pp. 3077-3093 ◽  
Author(s):  
Olivier Pauluis ◽  
Arnaud Czaja ◽  
Robert Korty
Keyword(s):  
Mass Transport ◽  
Total Mass ◽  
Potential Temperature ◽  
Equivalent Potential Temperature ◽  
Moist Air ◽  
Low Level ◽  
Equivalent Potential ◽  
Entropy Transport ◽  
Mean Circulation ◽  
The Tropics

Abstract Differential heating of the earth’s atmosphere drives a global circulation that transports energy from the tropical regions to higher latitudes. Because of the turbulent nature of the flow, any description of a “mean circulation” or “mean parcel trajectories” is tied to the specific averaging method and coordinate system. In this paper, the NCEP–NCAR reanalysis data spanning 1970–2004 are used to compare the mean circulation obtained by averaging the flow on surfaces of constant liquid water potential temperature, or dry isentropes, and on surfaces of constant equivalent potential temperature, or moist isentropes. While the two circulations are qualitatively similar, they differ in intensity. In the tropics, the total mass transport on dry isentropes is larger than the circulation on moist isentropes. In contrast, in midlatitudes, the total mass transport on moist isentropes is between 1.5 and 3 times larger than the mass transport on dry isentropes. It is shown here that the differences between the two circulations can be explained by the atmospheric transport of water vapor. In particular, the enhanced mass transport on moist isentropes corresponds to a poleward flow of warm moist air near the earth’s surface in midlatitudes. This low-level poleward flow does not appear in the zonally averaged circulation on dry isentropes, as it is hidden by the presence of a larger equatorward flow of drier air at same potential temperature. However, as the equivalent potential temperature in this low-level poleward flow is close to the potential temperature of the air near the tropopause, it is included in the total circulation on moist isentropes. In the tropics, the situation is reversed: the Hadley circulation transports warm moist air toward the equator, and in the opposite direction to the flow at upper levels, and the circulation on dry isentropes is larger than that on moist isentropes. The relationship between circulation and entropy transport is also analyzed. A gross stratification is defined as the ratio of the entropy transport to the net transport on isentropic surfaces. It is found that in midlatitudes the gross stability for moist entropy is approximately the same as that for dry entropy. The gross stratification in the midlatitude circulation differs from what one would expect for either an overturning circulation or horizontal mixing; rather, it confirms that warm moist subtropical air ascends into the upper troposphere within the storm tracks.

scholarly journals Isentropic Analysis of Convective Motions

2013 ◽  
Vol 70 (11) ◽  
pp. 3673-3688 ◽  
Author(s):  
Olivier M. Pauluis ◽  
Agnieszka A. Mrowiec
Keyword(s):  
Mass Transport ◽  
Gravity Waves ◽  
Mass Flux ◽  
Potential Temperature ◽  
Three Dimensional ◽  
High Energy ◽  
Equivalent Potential Temperature ◽  
Equivalent Potential ◽  
Convective Motions ◽  
The Mean

Abstract This paper analyzes the convective mass transport by sorting air parcels in terms of their equivalent potential temperature to determine an isentropic streamfunction. By averaging the vertical mass flux at a constant value of the equivalent potential temperature, one can compute an isentropic mass transport that filters out reversible oscillatory motions such as gravity waves. This novel approach emphasizes the fact that the vertical energy and entropy transports by convection are due to the combination of ascending air parcels with high energy and entropy and subsiding air parcels with lower energy and entropy. Such conditional averaging can be extended to other dynamic and thermodynamic variables such as vertical velocity, temperature, or relative humidity to obtain a comprehensive description of convective motions. It is also shown how this approach can be used to determine the mean diabatic tendencies from the three-dimensional dynamic and thermodynamic fields. A two-stream approximation that partitions the isentropic circulation into a mean updraft and a mean downdraft is also introduced. This offers a straightforward way to identify the mean properties of rising and subsiding air parcels. The results from the two-stream approximation are compared with two other definitions of the cloud mass flux. It is argued that the isentropic analysis offers a robust definition of the convective mass transport that is not tainted by the need to arbitrarily distinguish between convection and its environment, and that separates the irreversible convective overturning from oscillations associated with gravity waves.

scholarly journals Analysis of Possible Physical Factors That Accelerate Downdrafts in Storm Clouds over Cuba

2021 ◽  
Vol 8 (1) ◽  
pp. 23
Author(s):  
Gleisis Alvarez-Socorro ◽  
Mario Carnesoltas-Calvo ◽  
Alis Varela-de la Rosa ◽  
José C. Fernández-Alvarez
Keyword(s):  
Relative Humidity ◽  
Potential Temperature ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Physical Factors ◽  
Equivalent Potential Temperature ◽  
Minimum Relative Humidity ◽  
Equivalent Potential ◽  
Low Levels ◽  
Do So

One of the manifestations of severe local storms is strong linear winds, which are known as a downburst and which are capable of causing great losses to the country’s economy and society. Knowing which factors in the atmosphere are necessary for the occurrence of this phenomenon is essential for its better understanding and prediction. The objective of this study was to analyze the possible physical factors that accelerate downdrafts in the storm clouds in Cuba. To do so, 10 study cases simulated with the weather research and forecasting (WRF) model at 3 km of the spatial resolution were used. The factors capable of discriminating between downbursts and thunderstorms without severity were obtained. These were the absorption of latent heat by evaporation and fusion, the equivalent potential temperature difference between the level of maximum relative humidity in the low levels and of minimum relative humidity in the middle levels, the speed of the downdraft, and the downdraft available convective potential energy (DCAPE). Unlike previous research, they discriminated against updraft buoyancy and energy advection, both at the middle levels of the troposphere.

Atmospheric Overturning across Multiple Scales of an MJO Event during the CINDY/DYNAMO Campaign

2018 ◽  
Vol 75 (2) ◽  
pp. 381-399 ◽  
Author(s):  
Xingchao Chen ◽  
Olivier M. Pauluis ◽  
Fuqing Zhang
Keyword(s):  
Indian Ocean ◽  
Mass Transport ◽  
Multiple Scales ◽  
Potential Temperature ◽  
Intraseasonal Variability ◽  
Active Phase ◽  
Convective Activity ◽  
High Entropy ◽  
Equivalent Potential ◽  
Convective Scale

Abstract This study investigates the atmospheric overturning of the October 2011 MJO event observed during the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY)/DYNAMO field experiment using a cloud-permitting numerical model. The isentropic analysis is used to sort the vertical mass transport in terms of the equivalent potential temperature of the air parcels, which naturally decomposes the atmospheric overturning between ascending air with high entropy and subsiding air with low entropy. The circulation is further decomposed into contributions of four main scales: basinwide ascent, meridional overturning, regional overturning, and convection. Results show that the convective scale dominates the upward mass transport while larger scales play an important role both by allowing a deeper overturning and by modulating convective activity. There are substantial changes in the atmospheric overturning during different phases of this MJO event. Increased convective activity at low levels precedes the onset of the MJO by several days. The initiation of the MJO itself is associated with a substantial increase in the atmospheric overturning over the Indian Ocean. The subsequent eastward propagation of the MJO event can be clearly captured by the evolutions of convective-scale vertical mass fluxes at different altitudes. The equivalent potential temperatures of the rising and subsiding air parcels in the convective-scale overturning are also increased in the troposphere during the active phase of the MJO.

Comments on “A Third-Law Isentropic Analysis of a Simulated Hurricane”

2018 ◽  
Vol 75 (10) ◽  
pp. 3725-3733 ◽  
Author(s):  
Olivier M. Pauluis
Keyword(s):  
Numerical Simulation ◽  
Mass Transport ◽  
Coordinate Transformation ◽  
Potential Temperature ◽  
Equivalent Potential Temperature ◽  
Upper Troposphere ◽  
Equivalent Potential ◽  
Specific Choice ◽  
Third Law ◽  
Ice Water

The atmospheric overturning can be estimated by computing an isentropic streamfunction, defined as the net upward mass transport of all air parcels with the potential temperature less than a given threshold. Here, the streamfunctions for the equivalent potential temperature and the entropy potential temperature are compared in a numerical simulation of a hurricane. It is shown that, when condensate is not taken into account, the two streamfunctions are equivalent and can be related to one another by a coordinate transformation. When condensate content is included, the streamfunctions differ substantially in the upper troposphere because of the large amount of ice water found in some updrafts. It is also shown that using an equivalent potential temperature over ice avoids this problem and offers a more robust way to compute the atmospheric overturning when precipitation is included. While it has been recently recommended to limit the isentropic analysis to the entropy potential temperature, it is argued here that more insights can be gained by comparing a circulation averaged in multiple coordinates over limiting oneself to one specific choice.

Using Digital Cloud Photogrammetry to Characterize the Onset and Transition from Shallow to Deep Convection over Orography

2006 ◽  
Vol 134 (9) ◽  
pp. 2527-2546 ◽  
Author(s):  
Joseph A. Zehnder ◽  
Liyan Zhang ◽  
Dianne Hansford ◽  
Anshuman Radzan ◽  
Nancy Selover ◽  
...  
Keyword(s):  
Deep Convection ◽  
Potential Temperature ◽  
Threshold Value ◽  
Surface Fluxes ◽  
Cloud Base ◽  
Equivalent Potential Temperature ◽  
Shallow Convection ◽  
Thermodynamic Structure ◽  
Automated Method ◽  
Equivalent Potential

Abstract An automated method for segmenting digital images of orographic cumulus and a simple metric for characterizing the transition from shallow to deep convection are presented. The analysis is motivated by the hypothesis that shallow convection conditions the atmosphere for further deep convection by moistening it and preventing the evaporation of convective turrets through the entrainment of dry air. Time series of convective development are compared with sounding and surface data for 6 days during the summer of 2003. The observations suggest the existence of a threshold for the initiation of shallow convection based on the surface equivalent potential temperature and the saturated equivalent potential temperature above the cloud base. This criterion is similar to that controlling deep convection over the tropical oceans. The subsequent evolution of the convection depends on details of the environment. Surface fluxes of sensible and latent heat, along with the transport of boundary layer air by upslope flow, increase the surface equivalent potential temperature and once the threshold value is exceeded, shallow convection begins. The duration of the shallow convection period and growth rate of the deep convection are determined by the kinematic and thermodynamic structure of the mid- and upper troposphere.

scholarly journals Summertime Post-Cold-Frontal Marine Stratocumulus Transition Processes over the Eastern North Atlantic

2020 ◽  
Vol 77 (6) ◽  
pp. 2011-2037 ◽  
Author(s):  
Melissa kazemirad ◽  
Mark A. Miller
Keyword(s):  
North Atlantic ◽  
Marine Boundary Layer ◽  
Potential Temperature ◽  
Wrf Model ◽  
Cloud Base ◽  
Equivalent Potential Temperature ◽  
Cumulus Clouds ◽  
Equivalent Potential ◽  
Atmospheric Radiation Measurement ◽  
Eastern North Atlantic

Abstract Marine boundary layer (MBL) cloud morphology associated with two summertime cold fronts over the eastern North Atlantic (ENA) is investigated using high-resolution simulations from the Weather Research and Forecasting (WRF) Model and observations from the Atmospheric Radiation Measurement (ARM) ENA Climate Research Facility. Lagrangian trajectories are used to study the evolution of post-cold-frontal MBL clouds from solid stratocumulus to broken cumulus. Clouds within specified domains in the vicinity of transitions are classified according to their degree of decoupling, and cloud-base and cloud-top breakup processes are evaluated. The Lagrangian derivative of the surface latent heat flux is found to be strongly correlated with that of the cloud fraction at cloud base in the simulations. Cloud-top entrainment instability (CTEI) is shown to operate only in the decoupled MBL. A new indicator of inversion strength at cloud top that employs the vertical gradients of equivalent potential temperature and saturation equivalent potential temperature, which can be computed directly from soundings, is proposed as an alternative to CTEI. Overall, results suggest that the deepening–warming hypothesis suggested by Bretherton and Wyant explains many of the characteristics of the summertime postfrontal MBL evolution of cloud structure over the ENA, thereby widening the phase space over which the hypothesis may be applied. A subset of the deepening–warming hypothesis involving warming initially dominating over moistening is proposed. It is postulated that changes in climate change–induced modifications in cold-frontal structure over the ENA may be accompanied by coincident changes in the location and timing of MBL cloud transitions in the post-cold-frontal environment.

Rotating Shallow-Water Models with Moist Convection

2018 ◽  
Author(s):  
Vladimir Zeitlin
Keyword(s):  
Baroclinic Instability ◽  
Potential Temperature ◽  
Moist Convection ◽  
Mathematical Properties ◽  
Vertical Fluxes ◽  
Equivalent Potential ◽  
Shallow Water Models ◽  
Wave Emission ◽  
Rotating Shallow Water ◽  
Convective Fluxes

It is shown how the standard RSW can be ’augmented’ to include phase transitions of water. This chapter explains how to incorporate extra (convective) vertical fluxes in the model. By using Lagrangian conservation of equivalent potential temperature condensation of the water vapour, which is otherwise a passive tracer, is included in the model and linked to convective fluxes. Simple relaxational parameterisation of condensation permits the closure of the system, and surface evaporation can be easily included. Physical and mathematical properties of thus obtained model are explained, and illustrated on the example of wave scattering on the moisture front. The model is applied to ’moist’ baroclinic instability of jets and vortices. Condensation is shown to produce a transient increase of the growth rate. Special attention is paid to the moist instabilities of hurricane-like vortices, which are shown to enhance intensification of the hurricane, increase gravity wave emission, and generate convection-coupled waves.

What are the Best Thermodynamic Quantity and Function to Define a Front in Gridded Model Output?

2019 ◽  
Vol 100 (5) ◽  
pp. 873-895 ◽  
Author(s):  
Carl M. Thomas ◽  
David M. Schultz
Keyword(s):  
Real Time ◽  
Potential Temperature ◽  
Thermodynamic Quantity ◽  
Kinematics And Dynamics ◽  
Horizontal Gradient ◽  
Model Output ◽  
Equivalent Potential Temperature ◽  
Thermal Front ◽  
Equivalent Potential ◽  
Definition Of

AbstractFronts can be computed from gridded datasets such as numerical model output and reanalyses, resulting in automated surface frontal charts and climatologies. Defining automated fronts requires quantities (e.g., potential temperature, equivalent potential temperature, wind shifts) and kinematic functions (e.g., gradient, thermal front parameter, and frontogenesis). Which are the most appropriate to use in different applications remains an open question. This question is investigated using two quantities (potential temperature and equivalent potential temperature) and three functions (magnitude of the horizontal gradient, thermal front parameter, and frontogenesis) from both the context of real-time surface analysis and climatologies from 38 years of reanalyses. The strengths of potential temperature to identify fronts are that it represents the thermal gradients and its direct association with the kinematics and dynamics of fronts. Although climatologies using potential temperature show features associated with extratropical cyclones in the storm tracks, climatologies using equivalent potential temperature include moisture gradients within air masses, most notably at low latitudes that are unrelated to the traditional definition of a front, but may be representative of a broader definition of an airmass boundary. These results help to explain previously published frontal climatologies featuring maxima of fronts in the subtropics and tropics. The best function depends upon the purpose of the analysis, but Petterssen frontogenesis is attractive, both for real-time analysis and long-term climatologies, in part because of its link to the kinematics and dynamics of fronts. Finally, this study challenges the conventional definition of a front as an airmass boundary and suggests that a new, dynamically based definition would be useful for some applications.

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