scholarly journals Examination of effects of aerosols on a pyroCb and their dependence on fire intensity and aerosol perturbation

2020 ◽  
Vol 20 (6) ◽  
pp. 3357-3371
Author(s):  
Seoung Soo Lee ◽  
George Kablick III ◽  
Zhanqing Li ◽  
Chang Hoon Jung ◽  
Yong-Sang Choi ◽  
...  
Keyword(s):  
Water Vapor ◽  
Heat Fluxes ◽  
Cirrus Clouds ◽  
Fire Intensity ◽  
Modeling Framework ◽  
Surface Heat Fluxes ◽  
Cloud Properties ◽  
Aerosol Effect ◽  
Weak Intensity ◽  
Weak Surface

Abstract. Using a modeling framework, this study investigates how a pyrocumulonimbus (pyroCb) event influences water vapor concentrations and cirrus-cloud properties near the tropopause, specifically focusing on how fire-produced aerosols affect this role. Results from a case study show that when observed fire intensity is high, there is an insignificant impact of fire-produced aerosols on the development of the pyroCb and associated changes in water vapor and cirrus clouds near the tropopause. However, as fire intensity weakens, effects of those aerosols on microphysical variables and processes such as droplet size and autoconversion increase. Due to this, aerosol-induced invigoration of convection is significant for pyroCb with weak-intensity fires and associated weak surface heat fluxes. This leads to a situation where there is a greater aerosol effect on the transport of water vapor to the upper troposphere and the production of cirrus clouds with weak-intensity fires, whereas this effect is muted with strong-intensity fires.

scholarly journals Examination of effects of aerosols on a pyroCb and their dependence on fire intensity and aerosol perturbation using a cloud-system resolving model

2019 ◽  
Author(s):  
Seoung Soo Lee ◽  
George Kablick III ◽  
Zhanqing Li
Keyword(s):  
Water Vapor ◽  
Heat Fluxes ◽  
Fire Intensity ◽  
Cirrus Cloud ◽  
Modeling Framework ◽  
Surface Heat Fluxes ◽  
Cloud Properties ◽  
Aerosol Effect ◽  
Weak Intensity ◽  
Weak Surface

Abstract. This study investigates how a pyrocumulonimbus (pyroCb) event influences water vapor concentrations and cirrus cloud properties near the tropopause, specifically focusing on how fire-produced aerosols affect this role via a modeling framework. Results from a case study show that when observed fire intensity is high, there is an insignificant impact of fire-produced aerosols on the convective development of the pyroCb and associated changes in water vapor and the amount of cirrus cloud near the tropopause. However, as fire intensity weakens, the effects of aerosols on microphysical variables and processes such as droplet size and autoconversion increase. Modeling results shown herein indicate that aerosol-induced invigoration of convection is significant for pyroCb with weak-intensity fires and associated weak surface heat fluxes. Thus, there is a greater aerosol effect on the transportation of water vapor to the upper troposphere and the production of cirrus cloud with weak-intensity fires, whereas these effects are muted with strong-intensity fires.

Trends of land surface heat fluxes on the Tibetan Plateau from 2001 to 2012

2017 ◽  
Vol 37 (14) ◽  
pp. 4757-4767 ◽  
Author(s):  
Cunbo Han ◽  
Yaoming Ma ◽  
Xuelong Chen ◽  
Zhongbo Su
Keyword(s):  
Tibetan Plateau ◽  
Land Surface ◽  
Surface Heat ◽  
Heat Fluxes ◽  
The Tibetan Plateau ◽  
Surface Heat Fluxes ◽  
Land Surface Heat Fluxes

A Positive Feedback Process Related to the Rapid Development of an Extratropical Cyclone over the Kuroshio/Kuroshio Extension

2018 ◽  
Vol 146 (2) ◽  
pp. 417-433 ◽  
Author(s):  
Hidetaka Hirata ◽  
Ryuichi Kawamura ◽  
Masaya Kato ◽  
Taro Shinoda
Keyword(s):  
Water Vapor ◽  
Positive Feedback ◽  
Heat Supply ◽  
Rapid Development ◽  
Kuroshio Extension ◽  
Heat Fluxes ◽  
Latent Heating ◽  
Sensible Heat ◽  
Feedback Process ◽  
The Kuroshio

Abstract The active roles of sensible heat supply from the Kuroshio/Kuroshio Extension in the rapid development of an extratropical cyclone, which occurred in the middle of January 2013, were examined by using a regional cloud-resolving model. In this study, a control experiment and three sensitivity experiments without sensible and latent heat fluxes from the warm currents were conducted. When the cyclone intensified, sensible heat fluxes from these currents become prominent around the cold conveyor belt (CCB) in the control run. Comparisons among the four runs revealed that the sensible heat supply facilitates deepening of the cyclone’s central pressure, CCB development, and enhanced latent heating over the bent-back front. The sensible heat supply enhances convectively unstable conditions within the atmospheric boundary layer along the CCB. The increased convective instability is released by the forced ascent associated with frontogenesis around the bent-back front, eventually promoting updraft and resultant latent heating. Additionally, the sensible heating leads to an increase in the water vapor content of the saturated air related to the CCB through an increase in the saturation mixing ratio. This increased water vapor content reinforces the moisture flux convergence at the bent-back front, contributing to the activation of latent heating. Previous research has proposed a positive feedback process between the CCB and latent heating over the bent-back front in terms of moisture supply from warm currents. Considering the above two effects of the sensible heat supply, this study revises the positive feedback process.

scholarly journals The West Coast Thermal Trough: Mesoscale Evolution and Sensitivity to Terrain and Surface Fluxes

2013 ◽  
Vol 141 (8) ◽  
pp. 2869-2896 ◽  
Author(s):  
Matthew C. Brewer ◽  
Clifford F. Mass ◽  
Brian E. Potter
Keyword(s):  
High Pressure ◽  
West Coast ◽  
Energy Equation ◽  
Potential Temperature ◽  
Wrf Model ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
The West ◽  
Surface Heat Fluxes ◽  
Thermodynamic Energy

Abstract Despite the significant impacts of the West Coast thermal trough (WCTT) on West Coast weather and climate, questions remain regarding its mesoscale structure, origin, and dynamics. Of particular interest is the relative importance of terrain forcing, advection, and surface heating on WCTT formation and evolution. To explore such questions, the 13–16 May 2007 WCTT event was examined using observations and simulations from the Weather Research and Forecasting (WRF) Model. An analysis of the thermodynamic energy equation for these simulations was completed, as well as sensitivity experiments in which terrain or surface fluxes were removed or modified. For the May 2007 event, vertical advection of potential temperature is the primary driver of local warming and WCTT formation west of the Cascades. The downslope flow that drives this warming is forced by easterly flow associated with high pressure over British Columbia, Canada. When the terrain is removed from the model, the WCTT does not form and high pressure builds over the northwest United States. When the WCTT forms on the east side of the Cascades, diabatic heating dominates over the other terms in the thermodynamic energy equation, with warm advection playing a small role. If surface heat fluxes are neglected, an area of low pressure remains east of the Cascades, though it is substantially attenuated.

On the Hyperbolicity of the Bulk Air–Sea Heat Flux Functions: Insights into the Efficiency of Air–Sea Moisture Disequilibrium for Tropical Cyclone Intensification

2021 ◽  
Vol 149 (5) ◽  
pp. 1517-1534
Author(s):  
Benjamin Jaimes de la Cruz ◽  
Lynn K. Shay ◽  
Joshua B. Wadler ◽  
Johna E. Rudzin
Keyword(s):  
Tropical Cyclone ◽  
Surface Wind ◽  
Heat Content ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Ocean Heat Uptake ◽  
Surface Heat Fluxes ◽  
Heat Uptake ◽  
Moisture Fluxes ◽  
New Perspective

AbstractSea-to-air heat fluxes are the energy source for tropical cyclone (TC) development and maintenance. In the bulk aerodynamic formulas, these fluxes are a function of surface wind speed U10 and air–sea temperature and moisture disequilibrium (ΔT and Δq, respectively). Although many studies have explained TC intensification through the mutual dependence between increasing U10 and increasing sea-to-air heat fluxes, recent studies have found that TC intensification can occur through deep convective vortex structures that obtain their local buoyancy from sea-to-air moisture fluxes, even under conditions of relatively low wind. Herein, a new perspective on the bulk aerodynamic formulas is introduced to evaluate the relative contribution of wind-driven (U10) and thermodynamically driven (ΔT and Δq) ocean heat uptake. Previously unnoticed salient properties of these formulas, reported here, are as follows: 1) these functions are hyperbolic and 2) increasing Δq is an efficient mechanism for enhancing the fluxes. This new perspective was used to investigate surface heat fluxes in six TCs during phases of steady-state intensity (SS), slow intensification (SI), and rapid intensification (RI). A capping of wind-driven heat uptake was found during periods of SS, SI, and RI. Compensation by larger values of Δq > 5 g kg−1 at moderate values of U10 led to intense inner-core moisture fluxes of greater than 600 W m−2 during RI. Peak values in Δq preferentially occurred over oceanic regimes with higher sea surface temperature (SST) and upper-ocean heat content. Thus, increasing SST and Δq is a very effective way to increase surface heat fluxes—this can easily be achieved as a TC moves over deeper warm oceanic regimes.

Subcloud and Cloud-Base Latent Heat Fluxes during Shallow Cumulus Convection

2019 ◽  
Vol 77 (3) ◽  
pp. 1081-1100 ◽  
Author(s):  
Neil P. Lareau
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Latent Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Cloud Base ◽  
Cumulus Convection ◽  
Mixing Ratio ◽  
Convective Boundary ◽  
Water Vapor Mixing Ratio

Abstract Doppler and Raman lidar observations of vertical velocity and water vapor mixing ratio are used to probe the physics and statistics of subcloud and cloud-base latent heat fluxes during cumulus convection at the ARM Southern Great Plains (SGP) site in Oklahoma, United States. The statistical results show that latent heat fluxes increase with height from the surface up to ~0.8Zi (where Zi is the convective boundary layer depth) and then decrease to ~0 at Zi. Peak fluxes aloft exceeding 500 W m−2 are associated with periods of increased cumulus cloud cover and stronger jumps in the mean humidity profile. These entrainment fluxes are much larger than the surface fluxes, indicating substantial drying over the 0–0.8Zi layer accompanied by moistening aloft as the CBL deepens over the diurnal cycle. We also show that the boundary layer humidity budget is approximately closed by computing the flux divergence across the 0–0.8Zi layer. Composite subcloud velocity and water vapor anomalies show that clouds are linked to coherent updraft and moisture plumes. The moisture anomaly is Gaussian, most pronounced above 0.8Zi and systematically wider than the velocity anomaly, which has a narrow central updraft flanked by downdrafts. This size and shape disparity results in downdrafts characterized by a high water vapor mixing ratio and thus a broad joint probability density function (JPDF) of velocity and mixing ratio in the upper CBL. We also show that cloud-base latent heat fluxes can be both positive and negative and that the instantaneous positive fluxes can be very large (~10 000 W m−2). However, since cloud fraction tends to be small, the net impact of these fluxes remains modest.

Sign in / Sign up

Export Citation Format

Share Document