scholarly journals High-Resolution Observations of the Trowal–Warm-Frontal Region of Two Continental Winter Cyclones

2007 ◽  
Vol 135 (5) ◽  
pp. 1629-1646 ◽  
Author(s):  
Joseph A. Grim ◽  
Robert M. Rauber ◽  
Mohan K. Ramamurthy ◽  
Brian F. Jewett ◽  
Mei Han
Keyword(s):  
High Resolution ◽  
Thermal Gradient ◽  
Cold Front ◽  
Leading Edge ◽  
The Other ◽  
Frontal Region ◽  
Dry Air ◽  
Warm Front ◽  
Upper Level ◽  
Different Origins

Abstract This paper compares the structure of the trough of warm air aloft (trowal)–warm-frontal region of two continental wintertime cyclones. The cyclones were observed over the central Great Lakes region during the Lake-Induced Convection Experiment/Snowband Dynamics Project field campaign. The cyclones had different origins, with the first forming east of the Colorado Rockies and the second forming over the Gulf of Mexico. They were associated with different upper-level flow regimes, one located just north of a nearly zonal jet and the other located just west of a nearly meridional jet. Both storms produced heavy swaths of snow across the states of Illinois, Wisconsin, and Michigan. High-resolution observations of frontal structure were made during flights of the National Center for Atmospheric Research Electra aircraft using dropsondes and the Electra Doppler Radar tail radar system. The high-resolution observations suggest a different arrangement of air masses in the trowal region compared with the classical occlusion model, where the trowal axis forms at the intersection of a warm front and a cold front that has overtaken and subsequently ascended the warm front. In both cyclones dry air intruded over the warm front, isolating the warm, moist airflow within the trowal airstream. Very sharp moisture gradients were present at the leading edge of the dry air in both cyclones. In each case, relative humidity differences of over 50% were observed over distances of 10–20 km. The thermal gradient near the leading edge of the dry air in one cyclone was diffuse, so that the moist–dry boundary could best be characterized as an upper-level humidity front. In the other cyclone, the thermal gradient was sharper and aligned with the moisture boundary and was best characterized as a cold front aloft. The analyses suggest that the classical conceptual model of the trowal, at least in some cyclones such as the two illustrated here, needs to be revised to include the possibility that the warm moist airstream aloft may sometimes be bounded on its south side by an upper-level front rather than a surface-based cold front. Since the two cyclones discussed here had different origins, tracks, and flow regimes, the similarity of their structure suggests that these features may be common.

scholarly journals Kinematic and Moisture Characteristics of a Nonprecipitating Cold Front Observed during IHOP. Part I: Across-Front Structures

2008 ◽  
Vol 136 (1) ◽  
pp. 147-172 ◽  
Author(s):  
Katja Friedrich ◽  
David E. Kingsmill ◽  
Cyrille Flamant ◽  
Hanne V. Murphey ◽  
Roger M. Wakimoto
Keyword(s):  
Cold Front ◽  
Microwave Radiometer ◽  
Gravity Current ◽  
Leading Edge ◽  
Wide Band ◽  
Sharp Change ◽  
Air Mass ◽  
Dry Air ◽  
Early Afternoon ◽  
Variable Nature

Abstract A wide array of ground-based and airborne instrumentation is used to examine the kinematic and moisture characteristics of a nonprecipitating cold front observed in west-central Kansas on 10 June 2002 during the International H2O Project (IHOP). This study, the first of two parts, is focused on describing structures in the across-front dimension. Coarsely resolved observations from the operational network and dropsondes deployed over a 200-km distance centered on the front are combined with higher-resolution observations from in situ sensors, Doppler radars, a microwave radiometer, and a differential absorption lidar that were collected across a ∼40-km swath that straddled a ∼100-km segment of the front. The northeast–southwest-oriented cold front moved toward the southeast at ∼8–10 m s−1 during the morning hours, but its motion slowed to less than 1 m s−1 in the afternoon. In the early afternoon, the cold front separated cool air with a northerly component flow of 2–4 m s−1 from a 10-km-wide band of hot, dry air with 5 m s−1 winds out of the south-southwest. The average updraft at the frontal interface was ∼0.5 m s−1 and slightly tilted back toward the cool air. A dryline was located to the southeast of the front, separating the hot, dry air mass from a warm, moist air mass composed of 10 m s−1 southerly winds. Later in the afternoon, the warm, moister air moved farther to the northwest, approaching the cold front. The dryline was still well observed in the southwestern part of the observational domain while it vanished almost completely in the northeastern part. Low-level convergence (∼1 × 10−3 s−1), vertical vorticity (∼0.5 × 10−3 s−1), and vertical velocity (∼1 m s−1) increased. The strong stable layer located at ∼2.0–2.5 km MSL weakened in the course of the afternoon, providing a basis for the development of isolated thunderstorms. The applicability of gravity current theory to the cold front was studied. There was evidence of certain gravity current characteristics, such as Froude numbers between 0.7 and 1.4, a pronounced feeder flow toward the leading edge, and a rotor circulation. Other characteristics, such as a sharp change in pressure and lobe and cleft structures, remain uncertain due to the temporally and spatially variable nature of the phenomenon and the coarse resolution of the measurements.

scholarly journals Wildfire Pyroconvection and CAPE: Buoyancy’s Drying and Atmospheric Intensification—Fort McMurray

Atmosphere ◽  
2020 ◽  
Vol 11 (7) ◽  
pp. 763
Author(s):  
Atoossa Bakhshaii ◽  
Edward A. Johnson ◽  
Kiana Nayebi
Keyword(s):  
Weather Prediction ◽  
Convective Available Potential Energy ◽  
Cumulus Cell ◽  
Leading Edge ◽  
Dew Point ◽  
Fire Plume ◽  
Fort Mcmurray ◽  
Dry Air ◽  
Short Period ◽  
Upper Level

The accurate prediction of wildfire behavior and spread is possible only when fire and atmosphere simulations are coupled. In this work, we present a mechanism that causes a small fire to intensify by altering the atmosphere. These alterations are caused by fire-related fluxes at the surface. The fire plume and fluxes increase the convective available potential energy (CAPE) and the chance of the development of a strong pyroconvection system. To study this possible mechanism, we used WRF-Fire to capture fire line propagation as the result of interactions between heat and moisture fluxes, pressure perturbations, wind shear development and dry air downdraft. The wind patterns and dynamics of the pyroconvection system are simulated for the Horse River wildfire at Fort McMurray, Canada. The results revealed that the updraft speed reached up to 12 m/s. The entrainment mixed the mid and upper-level dry air and lowered the atmospheric moisture. The mid-level and upper-level dew point temperature changed by 5–10 ∘ C in a short period of time. The buoyant air strengthened the ascent as soon as the nocturnal inversion was eliminated by daytime heating. The 887 J/kg total increase of CAPE in less than 5 h and the high bulk Richardson number (BRN) of 93 were indicators of the growing pyro-cumulus cell. The presented simulation has not improved the original model or supported leading-edge numerical weather prediction (NWP) achievements, except for adapting WRF-Fire for Canadian biomass fuel. However, we were able to present a great deal of improvements in wildfire nowcasting and short-term forecasting to save lives and costs associated with wildfires. The simulation is sufficiently fast and efficient to be considered for a real-time operational model. While the project was designed and succeeded as an NWP application, we are still searching for a solution for the intractable problems associated with political borders and the current liable authorities for the further development of a new generation of national atmosphere–wildfire forecasting systems.

scholarly journals Precursors to Convection over Peninsular India during March–May in AMSU-B Data

2006 ◽  
Vol 21 (5) ◽  
pp. 781-801 ◽  
Author(s):  
Dileep M. Puranik ◽  
R. N. Karekar
Keyword(s):  
Middle Level ◽  
The Other ◽  
Infrared Images ◽  
Peninsular India ◽  
Dry Air ◽  
Microwave Sounding Unit ◽  
Prior Literature ◽  
Microwave Sounding ◽  
Upper Level ◽  
High Level

Abstract In the present work the locations of precursors to summer thunderstorms over peninsular India are sought in images from the Advanced Microwave Sounding Unit-B (AMSU-B). At these locations, moisture maxima and brightness temperature (BT) minima may be expected. Prior literature suggests that the 150-GHz channel is useful in detecting the BT minima due to moisture in the lowest 1 km, the 183.3 ± 7- GHz channel is useful for detecting middle-level moist layers and clouds, and the other 183.3-GHz channels are useful for upper-air features such as high-level dry air incursion or upper-air troughs. Cloudy or moist pixels and low-emissivity ground pixels have similar BTs. The extraction of the locations of BT minima is therefore difficult. The scale 1 or 2 à trous wavelet transform (WT) allows unambiguous location of the BT minima due to clouds or moist regions from AMSU-B images. On 3–4 April 2001 there was a middle-level moisture incursion over the peninsula and on 17–18 April 2001 there was an upper-level dry air incursion. The wavelet components of AMSU-B data were extracted during these two events. From the Meteosat-5 infrared images it was verified that convection occurred within 2 h of the AMSU-B pass in the low-BT regions separated by the à trous WT. On the other hand, peninsular discontinuities on 3–4 April 2001 and 7 April 2002 and other days in 2002 showed that useful precursors could not be extracted from the 150-GHz signal. The BTs for the 150-GHz channel in dry air are affected significantly by ground altitude and by changes in surface emissivity. Failure and success in precursor detection are both attributed to the variability in the BTs.

scholarly journals Two Issues Concerning Surface Frontogenesis

2017 ◽  
Vol 74 (9) ◽  
pp. 2967-2987 ◽  
Author(s):  
Mankin Mak ◽  
Yi Lu ◽  
Yi Deng
Keyword(s):  
Diabatic Heating ◽  
Cold Front ◽  
Model Simulation ◽  
Wrf Model ◽  
Baroclinic Wave ◽  
Steering Flow ◽  
Warm Front ◽  
Surface Front ◽  
Upper Level ◽  
Ageostrophic Circulation

Abstract With the Weather Research and Forecasting (WRF) Model specifically configured to simulate the intensification and evolution of an extratropical baroclinic wave, this study first investigates why cold fronts are characteristically longer, narrower, and more intense than warm fronts in the extratropical atmosphere. It is found that the differential thermal advection by the geostrophic and ageostrophic wind components in the two frontal regions results in a greater thermal contrast across the cold front. The length of the cold front is essentially the length scale of the intensifying baroclinic wave (i.e., on the order of radius of deformation). The frontal system as a whole moves eastward under the influence of a steering flow. In addition, the cold front outpaces the warm front eastward, making the western portion of the warm front progressively occluded and the eastern portion of the warm front shorter. The dynamical processes tend to move the cold front eastward, whereas the diabatic heating processes tend to move it westward, contributing to the narrowness of the cold front. This study also investigates whether, how, and why an upper-level front (ULF) would synergistically interact with a surface front (SF). It is found that a favorable circumstance for such interaction to occur in an observed extratropical cyclone and in the WRF Model simulation is when the ULF and SF are roughly parallel to one another with the ULF aloft located a few hundred kilometers to the west of the SF. The relative importance of “forcing” for the ageostrophic circulation associated with the geostrophic circulation, diabatic heating, and friction are diagnosed in such interaction.

scholarly journals Occluded Fronts and the Occlusion Process: A Fresh Look at Conventional Wisdom

2011 ◽  
Vol 92 (4) ◽  
pp. 443-466 ◽  
Author(s):  
David M. Schultz ◽  
Geraint Vaughan
Keyword(s):  
Frontal Zone ◽  
Cold Front ◽  
Heavy Precipitation ◽  
Conventional Wisdom ◽  
The Other ◽  
Extratropical Cyclones ◽  
New Paradigm ◽  
Warm Front ◽  
Catch Up ◽  
By Catch

Traditionally, the formation of an occluded front during the occlusion process in extratropical cyclones has been viewed as the catch-up of a faster-moving cold front to a slower-moving warm front separating the warm-sector air from the low center, as first described in the Norwegian cyclone model over 90 yr ago. In this article, the conventional wisdom, or the commonly held beliefs originating from the Norwegian cyclone model, about occluded fronts and the occlusion process are critically examined. The following four tenets of this conventional wisdom are addressed. First, the occlusion process is better described not by catch-up, but by the wrapping up and lengthening of the warm-air tongue as a result of deformation and rotation around the low center. Second, the merger of the cold front and warm front does not result in the frontal zone with the warmer air ascending over the other frontal zone. Instead, the occluded frontal zone tilts over the more statically stable frontal zone. Because a warmfrontal zone tends to be more stable than a cold-frontal zone, this process usually produces a warm-type occlusion, confirming that cold-type occlusions are less common than warm-type occlusions. Third, occlusion does not mean that the cyclone has stopped deepening, because many cyclones continue to deepen 10–30 mb for 12–36 h after the formation of the occluded front. Fourth, clouds and precipitation associated with occluded fronts differ from their widespread stratiform depiction in textbooks. Embedded precipitation bands may be parallel to the front, and little relationship may exist between the fronts and the cloud mass. These four tenets help to explain anomalies in the Norwegian cyclone model, such as how occluded fronts that spiral around the low center do not require catch-up to form, how Shapiro–Keyser cyclones undergo occlusion, why some cyclones do not form occluded fronts, how some cyclones deepen after occlusion, why few cold-type occlusions have been observed, and why occluded cyclones are often associated with heavy precipitation. This reexamination of conventional wisdom leads to a new paradigm for occluded fronts and occluded cyclones. A supplement to this article is available online: DOI: 10.1175/2010BAMS3057.2

Computer-Controlled Hrem Alignment Using Automated Diffractogram Analysis

1990 ◽  
Vol 48 (1) ◽  
pp. 532-533
Author(s):  
G.Y. Fan ◽  
O.L. Krivanek
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
The Other ◽  
Full Information ◽  
Resolution Electron ◽  
Skilled Operator ◽  
Automatic Alignment ◽  
High Resolution Electron Microscope ◽  
Computer Controlled ◽  
Recorded Image

Full alignment of a high resolution electron microscope (HREM) requires five parameters to be optimized: the illumination angle (beam tilt) x and y, defocus, and astigmatism magnitude and orientation. Because neither voltage nor current centering lead to the correct illumination angle, all the adjustments must be done on the basis of observing contrast changes in a recorded image. The full alignment can be carried out by a computer which is connected to a suitable image pick-up device and is able to control the microscope, sometimes with greater precision and speed than even a skilled operator can achieve. Two approaches to computer-controlled (automatic) alignment have been investigated. The first is based on measuring the dependence of the overall contrast in the image of a thin amorphous specimen on the relevant parameters, the other on measuring the image shift. Here we report on our progress in developing a new method, which makes use of the full information contained in a computed diffractogram.

scholarly journals Neutron Imaging Using a Fine-Grained Nuclear Emulsion

2021 ◽  
Vol 7 (1) ◽  
pp. 4
Author(s):  
Katsuya Hirota ◽  
Tomoko Ariga ◽  
Masahiro Hino ◽  
Go Ichikawa ◽  
Shinsuke Kawasaki ◽  
...  
Keyword(s):  
Image Analysis ◽  
High Resolution ◽  
Neutron Detector ◽  
Nuclear Emulsion ◽  
Neutron Imaging ◽  
The Other ◽  
Crystal Oscillator ◽  
Fine Grained ◽  
Cold Neutrons ◽  
Track Analysis

A neutron detector using a fine-grained nuclear emulsion has a sub-micron spatial resolution and thus has potential to be applied as high-resolution neutron imaging. In this paper, we present two approaches to applying the emulsion detectors for neutron imaging. One is using a track analysis to derive the reaction points for high resolution. From an image obtained with a 9 μm pitch Gd grating with cold neutrons, periodic peak with a standard deviation of 1.3 μm was observed. The other is an approach without a track analysis for high-density irradiation. An internal structure of a crystal oscillator chip, with a scale of approximately 30 μm, was able to be observed after an image analysis.

High-Resolution Neutron Spectroscopy for the Investigation of Hydrogen Diffusion and Molecular Rotations in Solids

1993 ◽  
Vol 48 (1-2) ◽  
pp. 406-414
Author(s):  
T. Springer
Keyword(s):  
High Resolution ◽  
Hydrogen Diffusion ◽  
Quantum Effects ◽  
Quantum States ◽  
The Other ◽  
Neutron Spectroscopy ◽  
Impurity Atoms ◽  
Molecular Rotations ◽  
Rotational Motions ◽  
Diffusion Of Hydrogen

Abstract An introductory survey on applications of high-resolution neutron spectroscopy is presented, dealing with the motion of hydrogen in solids, namely concerning (i) random rotational motions or stationary tunneling states of NH+4-ions or CH3-groups, and (ii) diffusion of hydrogen in alloys. For the rotation of hydrogenous groups in solids, at higher temperatures rotational jumps can be found, whereas quantum states are observed by μeV-spectroscopy at temperatures below 50 K. On the other hand, hydrogen diffusion does not reveal pronounced evidence of quantum effects, except for hydrogen in a metal containing impurity atoms.

Hands Stencils in El Castillo Cave (Puente Viesgo, Cantabria, Spain). An Interdisciplinary Study

2021 ◽  
pp. 1-21
Author(s):  
Sergio Ripoll ◽  
Vicente Bayarri ◽  
Francisco J. Muñoz ◽  
Ricardo Ortega ◽  
Elena Castillo ◽  
...  
Keyword(s):  
High Resolution ◽  
Real Data ◽  
Digital Processing ◽  
The Other ◽  
Major Step ◽  
The People ◽  
High Resolution Images ◽  
Real Picture ◽  
Interdisciplinary Study ◽  
Very High

Our Palaeolithic ancestors did not make good representations of themselves on the rocky surfaces of caves and barring certain exceptions – such as the case of La Marche (found on small slabs of stone or plaquettes) or the Cueva de Ambrosio – the few known examples can only be referred to as anthropomorphs. As such, only hand stencils give us a real picture of the people who came before us. Hand stencils and imprints provide us with a large amount of information that allows us to approach not only their physical appearance but also to infer less tangible details, such as the preferential use of one hand over the other (i.e., handedness). Both new and/or mature technologies as well as digital processing of images, computers with the ability to process very high resolution images, and a more extensive knowledge of the Palaeolithic figures all help us to analyse thoroughly the hands in El Castillo cave. The interdisciplinary study presented here contributes many novel developments based on real data, representing a major step forward in knowledge about our predecessors.

scholarly journals Improvement in Surface Solar Irradiance Estimation Using HRV/MSG Data

2018 ◽  
Vol 10 (8) ◽  
pp. 1288 ◽  
Author(s):  
Filomena Romano ◽  
Domenico Cimini ◽  
Angela Cersosimo ◽  
Francesco Di Paola ◽  
Donatello Gallucci ◽  
...  
Keyword(s):  
High Resolution ◽  
Solar Irradiance ◽  
Research Council ◽  
National Research Council ◽  
The Other ◽  
Data Channel ◽  
The Difference ◽  
Photovoltaic Plants ◽  
Sky Conditions ◽  
Advanced Model

The Advanced Model for the Estimation of Surface Solar Irradiance (AMESIS) was developed at the Institute of Methodologies for Environmental Analysis of the National Research Council of Italy (IMAA-CNR) to derive surface solar irradiance from SEVIRI radiometer on board the MSG geostationary satellite. The operational version of AMESIS has been running continuously at IMAA-CNR over all of Italy since 2017 in support to the monitoring of photovoltaic plants. The AMESIS operative model provides two different estimations of the surface solar irradiance: one is obtained considering only the low-resolution channels (SSI_VIS), while the other also takes into account the high-resolution HRV channel (SSI_HRV). This paper shows the difference between these two products against simultaneous ground-based observations from a network of 63 pyranometers for different sky conditions (clear, overcast and partially cloudy). Comparable statistical scores have been obtained for both AMESIS products in clear and cloud situation. In terms of bias and correlation coefficient over partially cloudy sky, better performances are found for SSI_HRV (0.34 W/m2 and 0.995, respectively) than SSI_VIS (−33.69 W/m2 and 0.862) at the expense of the greater run-time necessary to process HRV data channel.

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