Formation of Extreme Cold-Air Pools in Elevated Sinkholes: An Idealized Numerical Process Study

2005 ◽  
Vol 133 (4) ◽  
pp. 925-941 ◽  
Author(s):  
Günther Zängl
Keyword(s):  
Water Vapor ◽  
Heat Conductivity ◽  
Ambient Air ◽  
Heat Fluxes ◽  
Strong Temperature Dependence ◽  
Radiative Heat Loss ◽  
Cold Air ◽  
Process Study ◽  
Ground Heat Flux ◽  
Extreme Cold

High-resolution numerical simulations with the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) are presented to investigate the processes leading to the formation of extreme cold-air pools in elevated sinkholes. The simulations are idealized in the sense that they are conducted with idealized model topography and with idealized large-scale conditions representing an undisturbed wintertime high pressure situation. After a number of model modifications, the temperature fields, radiative cooling rates, and sensible heat fluxes simulated by the model were in good agreement with the available observations, giving confidence that the model is suitable for this process study. The model results indicate a number of necessary preconditions for the formation of an extreme cold-air pool in a sinkhole. Apart from undisturbed clear weather, a small heat conductivity of the ground and an effective mechanism drying the low-level air during the cooling process are required. The importance of the heat conductivity results from the fact that the net cooling of the ground is only a small residual between the net radiative heat loss and the ground heat flux. As a consequence, extreme cooling events are strongly favored by the presence of freshly fallen powder snow. The necessity of a drying mechanism is related to the strong temperature dependence of the saturation vapor pressure, decreasing by a factor of about 2.5 per 10 K temperature decrease at temperatures below −20°C. Except in cases of very dry ambient air, a nocturnal cooling by 25 or 30 K (as observed in extreme cases) must be accompanied by an order-of-magnitude reduction of the water vapor mixing ratio to prevent the formation of fog. According to the simulations, the most effective drying mechanism is provided by the formation of ice clouds and the subsequent sedimentation of the ice particles. Near the surface, direct deposition of water vapor at the ground also seems to play a significant role.

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.

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.

Effect of Water Vapor and SOx in Air on the Cathodes of Solid Oxide Fuel Cells

2007 ◽  
Vol 1041 ◽  
Author(s):  
Seon Hye Kim ◽  
Toshihiro Ohshima ◽  
Yusuke Shiratori ◽  
Kohei Itoh ◽  
Kazunari Sasaki
Keyword(s):  
Water Vapor ◽  
Solid Oxide Fuel Cells ◽  
Degradation Mechanism ◽  
Chemical Species ◽  
Cell Voltage ◽  
Ambient Air ◽  
Open Circuit ◽  
Constant Current ◽  
Constant Current Density

AbstractAmbient air is used as an oxygen source in SOFCs to be commercialized. Various chemical species which can lead to poisoning of SOFC cathodes are included as minor constitutions in air, such as water vapor, SOx, NOx and NaCl etc. However, their effects on the cathode performance have not yet well known, even though they are expected to cause a degradation of the electrode performance and to reduce the long-term durability of SOFCs. Therefore, in this study, we focused on the poisoning caused by water vapor and SOx in the oxygen source to clarify their effects on SOFCs performances and to reveal the degradation mechanism of cathodes. SOFCs with typical electrolyte-supported structure were used in this work, which were composed with ScSZ (10 mol% Sc2O3, 1mol% CeO2, 89 mol% ZrO2) plate with the thickness of 200 µm as electrolyte, NiO-ScSZ (mixture of 56 wt% NiO and 44 wt% ScSZ) porous layer as anode, and two cathode layers of LSM ((La0.8Sr0.2)0.98MnO3) and LSM-ScSZ (mixture of 50 wt% LSM and 50 wt% ScSZ). Power generation characteristics of the cells had been analyzed by measuring cell voltage at a constant current density (200 mA/cm2) and by comparing changes in cell impedance, upon supplying the artificially-contaminated air with water vapor or SOx, to the SOFC cathodes at various operational temperatures. High-resolution FESEM (S-5200, Hitachi) was used to analyze microstructural changes caused by the impurities. Mg Kα radiation from a monochromatized X-ray source was used for XPS measurements (ESCA-3400, KRATOS). AC impedance was measured at various temperatures under the open circuit voltage condition by an impedance analyzer (Solatron 1255B/SI 1287, Solatron), in a frequency range from 0.1 to 105 Hz with an amplitude of 10 mV.

Hydrological functioning of irrigated maize crops in southwest France using Eddy Covariance measurements and a land surface model

2021 ◽  
Author(s):  
Oluwakemi Dare-Idowu ◽  
Lionel Jarlan ◽  
Aurore Brut ◽  
Valerie Le-Dantec ◽  
Vincent Rivalland ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Land Surface ◽  
Sap Flow ◽  
Heat Fluxes ◽  
Added Value ◽  
Surface Model ◽  
Data Set ◽  
Flow Measurements ◽  
Ground Heat Flux

<p>This study aims to analyze the main components of the energy and hydric budgets of irrigated maize in southwestern France. To this objective, the ISBA-A-gs (<span>Interactions between Soil, Biosphere, and Atmosphere) </span>is run over six maize growing seasons. As a preliminary step, the ability of the ISBA-A-gs model to predict the different terms of the energy and water budgets is assessed thanks to a large database of <em>in situ</em> measurements by comparing the single budget version of the model with the new Multiple Energy Balance version solving an energy budget separately for the soil and the vegetation. The <em>in situ</em> data set acquired at the Lamasquere site (43.48<sup>o</sup> N, 1.249<sup>o</sup> E) includes half-hourly measurements of sensible (H) and latent heat fluxes (LE) estimated by an Eddy Covariance system. Measurements also include net radiation (Rn), ground heat flux (G), plant transpiration with sap flow sensors, meteorological variables, and 15-days measurements of vegetation characteristics. The seasonal dynamics of the turbulent fluxes were properly reproduced by both configurations of the model with an R² ranging from 0.66 to 0.89, and a root mean square error lower than 48 W m<sup>-2</sup>. Statistical metrics showed that H was better predicted by MEB with R² of 0.80 in comparison to ISBA-Ags (0.73). However, the difference between the RMSE of ISBA-Ags and MEB during the well-developed stage of the plants for both H and LE does not exceed 8 W m<sup>-2</sup>. This implies that MEB only has a significant added value over ISBA-Ags when the soil and the canopy are not fully coupled, and over a heterogeneous field. Furthermore, this study made a comparison between the sap flow measurements and the transpiration simulated by ISBA-A-gs and MEB. A good dynamics was reproduced by ISBA-A-gs and MEB, although, MEB (R²= 0.91) provided a slightly more realistic estimation of the vegetation transpiration. Consequently, this study investigated the dynamics of the water budget during the growing maize seasons. Results indicated that drainage is almost null on the site, while the observed values of cumulative evapotranspiration that was higher than the water inputs are related to a shallow ground table that provides supplement water to the crop. This work provides insight into the modeling of water and energy exchanges over maize crops and opens perspectives for better water management of the crop in the future.</p>

On the use of a coupled ocean–atmosphere–wave model during an extreme cold air outbreak over the Adriatic Sea

2016 ◽  
Vol 172-173 ◽  
pp. 48-65 ◽  
Author(s):  
Antonio Ricchi ◽  
Mario Marcello Miglietta ◽  
Pier Paolo Falco ◽  
Alvise Benetazzo ◽  
Davide Bonaldo ◽  
...  
Keyword(s):  
Adriatic Sea ◽  
Wave Model ◽  
Cold Air ◽  
Cold Air Outbreak ◽  
Ocean Atmosphere ◽  
Extreme Cold

Shivering onset, metabolic response, and convective heat transfer during cold air exposure

1991 ◽  
Vol 70 (5) ◽  
pp. 1996-2002 ◽  
Author(s):  
P. Tikuisis ◽  
D. G. Bell ◽  
I. Jacobs
Keyword(s):  
Heat Transfer ◽  
Metabolic Rate ◽  
Body Fat ◽  
Convective Heat ◽  
Heat Fluxes ◽  
Air Exposure ◽  
Cold Air ◽  
Convective Heat Loss ◽  
Norm Group ◽  
Lean Group

The onset and intensity of shivering of various muscles during cold air exposure are quantified and related to increases in metabolic rate and convective heat loss. Thirteen male subjects resting in a supine position and wearing only shorts were exposed to 10 degrees C air (42% relative humidity and less than 0.4 m/s airflow) for 2 h. Measurements included surface electromyogram recordings at six muscle sites representing the trunk and limb regions of one side of the body, temperatures and heat fluxes at the same contralateral sites, and metabolic rate. The subjects were grouped according to lean (LEAN, n = 6) and average body fat (NORM, n = 7) content. While the rectal temperatures fluctuated slightly but not significantly during exposure, the skin temperature decreased greatly, more at the limb sites than at the trunk sites. Muscles of the trunk region began to shiver sooner and at a higher intensity than those of the limbs. The intensity of shivering and its increase over time of exposure were consistent with the increase in the convective heat transfer coefficient calculated from skin temperatures and heat fluxes. Both the onset of shivering and the magnitude of the increase in metabolic rate due to shivering were higher for the LEAN group than for the NORM group. A regression analysis indicates that, for a given decrease in mean skin temperature, the increase in metabolic rate due to shivering is attenuated by the square root of percent body fat. Thus the LEAN group shivered at higher intensity, resulting in higher increases in metabolic heat production and convective heat loss during cold air exposure than did the NORM group.

The Climatology, Meteorology, and Boundary Layer Structure of Marine Cold Air Outbreaks in Both Hemispheres*

2016 ◽  
Vol 29 (6) ◽  
pp. 1999-2014 ◽  
Author(s):  
Jennifer Fletcher ◽  
Shannon Mason ◽  
Christian Jakob
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Zonal Flow ◽  
Heat Fluxes ◽  
Pressure Gradients ◽  
Cold Air ◽  
Surface Heat Fluxes ◽  
Cold Air Outbreak ◽  
Wide Range ◽  
Cold Air Outbreaks

Abstract A comparison of marine cold air outbreaks (MCAOs) in the Northern and Southern Hemispheres is presented, with attention to their seasonality, frequency of occurrence, and strength as measured by a cold air outbreak index. When considered on a gridpoint-by-gridpoint basis, MCAOs are more severe and more frequent in the Northern Hemisphere (NH) than the Southern Hemisphere (SH) in winter. However, when MCAOs are viewed as individual events regardless of horizontal extent, they occur more frequently in the SH. This is fundamentally because NH MCAOs are larger and stronger than those in the SH. MCAOs occur throughout the year, but in warm seasons and in the SH they are smaller and weaker than in cold seasons and in the NH. In both hemispheres, strong MCAOs occupy the cold air sector of midlatitude cyclones, which generally appear to be in their growth phase. Weak MCAOs in the SH occur under generally zonal flow with a slight northward component associated with weak zonal pressure gradients, while weak NH MCAOs occur under such a wide range of conditions that no characteristic synoptic pattern emerges from compositing. Strong boundary layer deepening, warming, and moistening occur as a result of the surface heat fluxes within MCAOs.

Flow Visualization and Air Temperature Measurements in Symmetrically Heated Vertical Channels With Adiabatic Extensions

2002 ◽  
Author(s):  
Oronzio Manca ◽  
Marilena Musto ◽  
Vincenzo Naso
Keyword(s):  
Flow Visualization ◽  
Air Temperature ◽  
Process Parameters ◽  
Thermal Performance ◽  
Vertical Channel ◽  
Ambient Air ◽  
Expansion Ratio ◽  
Uniform Heat Flux ◽  
Thermal Plume ◽  
Cold Air

Air natural convection in a vertical channel-chimney system with the channel walls symmetrically heated at a uniform heat flux has been experimentally investigated. Flow visualization photographs and average air temperatures are presented. Some profiles of air temperature fluctuations are reported, which point out the fluid flow interactions in the chinmey. The flow visualization showed that the cold air inflow penetrating into the chimney affects the thermal performance of the channel. The improvement in the thermal performance of the channel determined by the chimney effect, for various values of the process parameters, has also been pointed out. In all investigated configurations and ranges of the process parameters the air flow in the channel was laminar. The flow in the chimney is strongly affected by the aspect ratio. Moreover, at the lower values of the expansion ratio the flow was laminar in the chimney and in its lower corner a stable vortex was noticed whereas at larger values of the expansion ratio a cold ambient air downflow worsened the thermal performance of the system. Interactions between the thermal plume arising from the channel, the vortex in the comer in the inlet chimney region and the cold air inflow yield fluctuations in the air temperature in the system. The distribution of time averaged air temperature in the cross sections validates indications given by the flow visualization in the chimney.

Effects of atropine on potentiation of exercise-induced bronchospasm by cold air

1978 ◽  
Vol 45 (2) ◽  
pp. 238-243 ◽  
Author(s):  
E. C. Deal ◽  
E. R. McFadden ◽  
R. H. Ingram ◽  
J. J. Jaeger
Keyword(s):  
Ambient Air ◽  
Small Airways ◽  
Flow Limitation ◽  
Ambient Conditions ◽  
Cold Air ◽  
Relative Contribution ◽  
Maximal Expiratory Flow ◽  
Before And After ◽  
Expiratory Flow ◽  
Exercise Induced

The role of vagal efferent activity in the cold air potentiation of exercise-induced asthma was assessed by exercising nine subjects who breathed air at ambient and subfreezing temperatures before and after cholinergic blockade. Lung volumes and maximal expiratory flow volume curves with air and with 80% helium-20% oxygen were obtained before and 5--10 min after each challenge. Isovolume comparisons of maximal expiratory flow rates with the two gases were used to assess relative contributions of large and small airways to flow limitation. Exercise under ambient conditions resulted in the expected airway obstruction and cold air exaggerated the response. Atropine pretreatment had no effect on the cold air potentiation. After atropine with ambient air exercise, there was an increase in the relative contribution of large airways to flow limitation, whereas exercise with cold air resulted in an increase in the contribution of small airways. We concluded that the potentiating effects of cold air are local and suggest that the immediate stimulus is related to cooling of intrathoracic airways.

Water vapor interference in the measurement of ozone in ambient air by ultraviolet absorption

1991 ◽  
Vol 62 (1) ◽  
pp. 223-228 ◽  
Author(s):  
C. P. Meyer ◽  
C. M. Elsworth ◽  
I. E. Galbally
Keyword(s):  
Water Vapor ◽  
Ambient Air ◽  
Ultraviolet Absorption
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