scholarly journals Synoptic‐scale and mesoscale controls for tornadogenesis on cold fronts: shear‐zone vortex‐genesis in a developing frontal wave

2021 ◽  
Author(s):  
M. R. Clark ◽  
D. J. Parker ◽  
K. E. Hanley
Keyword(s):  
Shear Zone ◽  
Synoptic Scale ◽  
Frontal Wave ◽  
Cold Fronts

scholarly journals Deep Learning for Spatially Explicit Prediction of Synoptic-Scale Fronts

2019 ◽  
Vol 34 (4) ◽  
pp. 1137-1160 ◽  
Author(s):  
Ryan Lagerquist ◽  
Amy McGovern ◽  
David John Gagne II
Keyword(s):  
Deep Learning ◽  
Weather Prediction ◽  
Potential Temperature ◽  
Probability Of Detection ◽  
Neural Nets ◽  
Specific Humidity ◽  
Synoptic Scale ◽  
Cold Fronts ◽  
Critical Success ◽  
The North

AbstractThis paper describes the use of convolutional neural nets (CNN), a type of deep learning, to identify fronts in gridded data, followed by a novel postprocessing method that converts probability grids to objects. Synoptic-scale fronts are often associated with extreme weather in the midlatitudes. Predictors are 1000-mb (1 mb = 1 hPa) grids of wind velocity, temperature, specific humidity, wet-bulb potential temperature, and/or geopotential height from the North American Regional Reanalysis. Labels are human-drawn fronts from Weather Prediction Center bulletins. We present two experiments to optimize parameters of the CNN and object conversion. To evaluate our system, we compare the objects (predicted warm and cold fronts) with human-analyzed warm and cold fronts, matching fronts of the same type within a 100- or 250-km neighborhood distance. At 250 km our system obtains a probability of detection of 0.73, success ratio of 0.65 (or false-alarm rate of 0.35), and critical success index of 0.52. These values drastically outperform the baseline, which is a traditional method from numerical frontal analysis. Our system is not intended to replace human meteorologists, but to provide an objective method that can be applied consistently and easily to a large number of cases. Our system could be used, for example, to create climatologies and quantify the spread in forecast frontal properties across members of a numerical weather prediction ensemble.

scholarly journals Diagnosis of Frontal Instabilities over the Southern Ocean

2005 ◽  
Vol 133 (4) ◽  
pp. 863-875 ◽  
Author(s):  
Jérôme Patoux ◽  
Gregory J. Hakim ◽  
Robert A. Brown
Keyword(s):  
Southern Ocean ◽  
Wind Field ◽  
Large Scale ◽  
Harmonic Component ◽  
Environmental Flow ◽  
Surface Winds ◽  
Synoptic Scale ◽  
Frontal Wave ◽  
The Third ◽  
Favorable Configuration

The development of three fronts over the Southern Ocean is described using SeaWinds-on-QuikSCAT scatterometer surface winds and an attribution technique to partition the wind field in three components: nondivergent and irrotational components at the scale of the front, and the remaining harmonic component (or environmental flow) induced by the synoptic-scale flow. The front and the environment in which the front is embedded are analyzed separately. A frontal wave is shown to develop out of the first front when the large-scale alongfront stretching decreases, the environmental flow becomes frontolytic, and a connection with the upper levels is established. In the second case, the stretching remains relatively strong and no frontal wave develops. The third front exhibits a developing wave but is not in a favorable configuration with the upper levels; the frontal wave does not deepen significantly.

scholarly journals A 6-yr Climatology of Fronts Affecting Helsinki, Finland, and Their Boundary Layer Structure

2013 ◽  
Vol 52 (9) ◽  
pp. 2106-2124 ◽  
Author(s):  
Victoria A. Sinclair
Keyword(s):  
Boundary Layer ◽  
Temperature Change ◽  
Frontal Zone ◽  
Layer Structure ◽  
Time Of Day ◽  
Lapse Rate ◽  
Maximum Temperature ◽  
Synoptic Scale ◽  
Boundary Layer Structure ◽  
Cold Fronts

AbstractA 6-yr climatology of the frequency, characteristics, and boundary layer structure of synoptic-scale fronts in Helsinki, Finland, was created using significant weather charts and observations from a 327-m-tall mast and from the Station for Measuring Ecosystem–Atmosphere Relationships III. In total, 855 fronts (332 cold fronts, 236 warm fronts, and 287 occluded fronts) affected Helsinki during the 6-yr period, equating to one front every 2.6 days. Seasonal and diurnal cycles were observed, with frontal frequency peaking during the cold season and during daytime. Composites of warm and cold fronts were developed to provide observationally based conceptual models of the low-level structure of fronts at the end of the North Atlantic Ocean storm track. The composite warm front displays a temperature increase of 4.0°C; a broad, forward-tilting frontal zone; and prolonged, weak-to-moderate precipitation. The composite cold front is characterized by a temperature decrease of 4.4°C, a narrow and slightly rearward-tilting frontal zone, and moderate precipitation collocated with the surface front. Relationships between frontal characteristics and the direction from which fronts approached, the season, time of day, prefrontal boundary layer lapse rate, and the location of the wind shift relative to the thermal gradient were investigated. The prefrontal lapse rate was the single most important variable in determining the temperature change, the height of the maximum temperature change, and the near-surface tilt of both warm and cold fronts. This result demonstrates the interaction between boundary layer and synoptic-scale processes that must be captured by numerical weather prediction models to accurately forecast surface fronts.

scholarly journals Use of Synthetic Aperture Radar in Finescale Surface Analysis of Synoptic-Scale Fronts at Sea

2005 ◽  
Vol 20 (3) ◽  
pp. 311-327 ◽  
Author(s):  
G. S. Young ◽  
T. N. Sikora ◽  
N. S. Winstead
Keyword(s):  
North America ◽  
Synthetic Aperture Radar ◽  
East Coast ◽  
Gulf Of Alaska ◽  
Data Sources ◽  
Synthetic Aperture ◽  
Synoptic Scale ◽  
Sar Images ◽  
Cold Fronts ◽  
Aperture Radar

Abstract The viability of synthetic aperture radar (SAR) as a tool for finescale marine meteorological surface analyses of synoptic-scale fronts is demonstrated. In particular, it is shown that SAR can reveal the presence of, and the mesoscale and microscale substructures associated with, synoptic-scale cold fronts, warm fronts, occluded fronts, and secluded fronts. The basis for these findings is the analysis of some 6000 RADARSAT-1 SAR images from the Gulf of Alaska and from off the east coast of North America. This analysis yielded 158 cases of well-defined frontal signatures: 22 warm fronts, 37 cold fronts, 3 stationary fronts, 32 occluded fronts, and 64 secluded fronts. The potential synergies between SAR and a range of other data sources are discussed for representative fronts of each type.

scholarly journals Wind power variability during the passage of cold fronts across South Africa

2019 ◽  
Vol 30 (3) ◽  
pp. 52-67 ◽  
Author(s):  
Amaris Dalton ◽  
Bernard Bekker ◽  
Andries Kruger
Keyword(s):  
South Africa ◽  
Wind Power ◽  
Cold Front ◽  
Power Production ◽  
Strong Wind ◽  
Synoptic Scale ◽  
Weather Patterns ◽  
Cold Fronts ◽  
Geographically Dispersed ◽  
Wind Resource

Wind is a naturally variable resource that fluctuates across timescales and, by the same token, the electricity generated by wind also fluctuates across timescales. At longer timescales, i.e., hours to days, synoptic-scale weather systems, notably cold fronts during South African winter months, are important instigators of strong wind conditions and variability in the wind resource. The variability of wind power production from aggregates of geographically disperse turbines for the passage of individual cold fronts over South Africa was simulated in this study. When considering wind power variability caused by synoptic-scale weather patterns, specifically cold fronts, the timescale at which analysis is conducted was found to be of great importance, as relatively small mean absolute power ramps at a ten-minute temporal resolution, order of 2-4% of simulated capacity, can result in large variations of total wind power production (at the order of 32–93% of simulated capacity) over a period of three to four days as a cold front passes. It was found that when the aggregate consists of a larger and more geographically dispersed set of turbines, as opposed to a smaller set of turbines specifically located within cold-front dominated high wind areas, variability and the mean absolute ramp rates decrease (or gets ‘smoothed’) across the timescales considered. It was finally shown that the majority of large simulated wind power ramp events observed during the winter months, especially at longer timescales, are caused by the passage of cold fronts. 

Contribution of cold fronts to seasonal rainfall in simulations over the southern La Plata Basin

2016 ◽  
Vol 68 (2-3) ◽  
pp. 243-255 ◽  
Author(s):  
EM de Jesus ◽  
RP da Rocha ◽  
MS Reboita ◽  
M Llopart ◽  
LM Mosso Dutra ◽  
...  
Keyword(s):  
Seasonal Rainfall ◽  
La Plata ◽  
Cold Fronts ◽  
La Plata Basin
Sign in / Sign up

Export Citation Format

Share Document