Neighboring upper level jet streaks, their proximity, and their synergestic coupling of the divergent regions

Abstract An examination of severe wind-producing mesoscale convective systems that occur in environments of very limited moisture is presented. Such systems, herein referred to as low-dewpoint derechos (LDDs), are difficult to forecast as they form in regions where the level of convective instability is well below that normally associated with severe convective weather. Using a dataset consisting of 12 LDDs that affected various parts of the continental United States, composite surface and upper-level analyses are constructed. These are used to identify factors that appear to be associated with LDD initiation and sustenance. It is shown that LDDs occur in mean kinematic and thermodynamic patterns notably different from those associated with most derechos. LDDs typically form along or just ahead of cold fronts, in the exit region of strong, upper-level jet streaks. Based on the juxtaposition of features in the composite analysis, it appears that linear forcing for ascent provided by the front, and/or ageostrophic circulations associated with the jet streak, induce the initial convective development where the lower levels are relatively dry, but lapse rates are steep. This convection subsequently grows upscale as storm downdrafts merge. The data further suggest that downstream cell propagation follows in the form of sequential, downwind-directed microbursts. Largely unidirectional wind profiles promote additional downwind-directed storm development and system sustenance until the LDD ultimately moves beyond the region supportive of forced convective initiation.

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A 10-Yr Climatology Relating the Locations of Reported Tornadoes to the Quadrants of Upper-Level Jet Streaks

Weather and Forecasting ◽

10.1175/1520-0434(2004)019<0301:aycrtl>2.0.co;2 ◽

2004 ◽

Vol 19 (2) ◽

pp. 301-309 ◽

Cited By ~ 21

Author(s):

Stanley F. Rose ◽

Peter V. Hobbs ◽

John D. Locatelli ◽

Mark T. Stoelinga

Keyword(s):

Upper Level ◽

Jet Streaks ◽

Upper Level Jet

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The Extratropical Transition of Tropical Cyclone Edisoana (1990)

Monthly Weather Review ◽

10.1175/mwr-d-13-00282.1 ◽

2014 ◽

Vol 142 (8) ◽

pp. 2772-2793 ◽

Cited By ~ 15

Author(s):

Kyle S. Griffin ◽

Lance F. Bosart

Keyword(s):

Tropical Cyclones ◽

Polar Front ◽

Lower Latitude ◽

Extratropical Transition ◽

Southwest Indian Ocean ◽

Half Wavelength ◽

Lower Amplitude ◽

Upper Level ◽

Jet Streaks ◽

Upper Level Jet

Abstract Documentation of southwest Indian Ocean (SWIO) tropical cyclones (TCs) and extratropical transition (ET) events is sparse in the refereed literature. The authors present a climatology of SWIO TC and ET events for 1989–2013. The SWIO averages ~9 tropical cyclones (TCs) per year in this modern era. Of these TCs, ~44% undergo extratropical transition (ET), or ~four per year. A case study of TC Edisoana (1990), the most rapidly intensifying SWIO post-ET TC between 1989 and 2013, shows that extratropical interactions began when an approaching trough embedded in the subtropical jet stream (STJ) induced ET on 7 March. As Edisoana underwent ET, a subtropical ridge downstream amplified in response to poleward-directed positive potential vorticity (PV) advection associated with diabatically (convectively) driven upper-level outflow from TC Edisoana. This amplifying lower-latitude ridge phased with a lower-amplitude higher-latitude ridge embedded in the polar front jet (PFJ), resulting in the merger of the two jets. This ridge phasing and jet merger, combined with the approach of an upstream trough embedded in the PFJ, resulted in a decrease in the half-wavelength between the approaching trough and the downstream phased ridges and provided extratropical cyclone Edisoana with a prime environment for rapid reintensification (RI). Poleward-directed positive PV advection into the phased ridge strengthened the upper-level jet downstream of Edisoana, which provided the primary baroclinic forcing throughout the RI phase. A backward trajectory analysis suggests that strong diabatic heating enhanced favorable synoptic-scale forcing for ascent from the upstream and downstream jet streaks and played a crucial role in the deepening of Edisoana through the ET and RI periods.

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Multiscale aspects of the 26–27 April 2011 tornado outbreak. Part II: Environmental modifications and upscale feedbacks arising from latent processes

Monthly Weather Review ◽

10.1175/mwr-d-21-0014.1 ◽

2021 ◽

Author(s):

Manda B. Chasteen ◽

Steven E. Koch

Keyword(s):

Large Scale ◽

Vertical Wind Shear ◽

Convective Systems ◽

Upper Level ◽

Large Scale Flow ◽

Jet Streaks ◽

Upper Level Jet ◽

Jet Structure ◽

Tornado Outbreaks ◽

Jet Streak

AbstractOne of the most prolific tornado outbreaks ever documented occurred on 26–27 April 2011 and comprised three successive episodes of tornadic convection that culminated with the development of numerous long-track, violent tornadoes over the southeastern U.S. during the afternoon of 27 April. This notorious afternoon supercell outbreak was preceded by two quasi-linear convective systems (hereafter QLCS1 and QLCS2), the first of which was an anomalously severe nocturnal system that rapidly grew upscale during the previous evening. In this Part II, we use a series of RUC 1-h forecasts and output from convection-permitting WRF-ARW simulations configured both with and without latent heat release to investigate how environmental modifications and upscale feedbacks produced by the two QLCSs contributed to the evolution and exceptional severity of this multi-episode outbreak.QLCS1 was primarily responsible for amplifying the large-scale flow pattern, inducing two upper-level jet streaks, and promoting secondary surface cyclogenesis downstream from the primary baroclinic system. Upper-level divergence markedly increased after QLCS1 developed, which yielded strong isallobaric forcing that rapidly strengthened the low-level jet (LLJ) and vertical wind shear over the warm sector and contributed to the system’s upscale growth and notable severity. Moreover, QLCS2 modified the mesoscale environment prior to the supercell outbreak by promoting the downstream formation of a pronounced upper-level jet streak, altering the midlevel jet structure, and furthering the development of a highly ageostrophic LLJ over the Southeast. Collectively, the flow modifications produced by both QLCSs contributed to the notably favorable shear profiles present during the afternoon supercell outbreak.

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Climatology of Storm Reports Relative to Upper-Level Jet Streaks

Weather and Forecasting ◽

10.1175/2009waf2222216.1 ◽

2009 ◽

Vol 24 (4) ◽

pp. 1032-1051 ◽

Cited By ~ 23

Author(s):

Adam J. Clark ◽

Christopher J. Schaffer ◽

William A. Gallus ◽

Kaj Johnson-O’Mara

Keyword(s):

Vertical Velocity ◽

Conceptual Models ◽

Temporal Trends ◽

Vertical Motion ◽

Upper Level ◽

Jet Streaks ◽

Upper Level Jet ◽

Four Quadrant ◽

The Right ◽

Jet Streak

Abstract Using quasigeostrophic arguments and numerical simulations, past works have developed conceptual models of vertical circulations induced by linear and curved jet streaks. Because jet-induced vertical motion could influence the development of severe weather, these conceptual models, especially the “four quadrant” model for linear jet streaks, are often applied by operational forecasters. The present study examines the climatology of tornado, hail, and severe wind reports relative to upper-level jet streaks, along with temporal trends in storm report frequencies and changes in report distributions for different jet streak directions. In addition, composite fields (e.g., divergence, vertical velocity) are analyzed for jet streak regions to examine whether the fields correspond to what is expected from conceptual models of curved or linear jet streaks, and whether the fields help explain the storm report distributions. During the period analyzed, 84% of storm reports were associated with upper-level jet streaks, with June–August having the lowest percentages. In March and April the left-exit quadrant had the most storm reports, while after April the right-entrance quadrant was associated with the most reports. Composites revealed that tornado and hail reports are concentrated in the jet-exit region along the major jet axis and in the right-entrance quadrant. Wind reports have similar maxima, but the right-entrance quadrant maximum is more pronounced. Upper-level composite divergence fields generally correspond to what would be expected from the four-quadrant model, but differences in the magnitudes of the vertical velocity between the quadrants and locations of divergent–convergent centers may have resulted from jet curvature. The maxima in the storm report distributions are not well collocated with the maxima in the upper-level divergence fields, but are much better collocated with low-level convergence maxima that exist in both exit regions and extend into the right-entrance region. Composites of divergence–convergence with linear, cyclonic, and anticyclonic jet streaks also generally matched conceptual models for curved jet streaks, and it was found that wind reports have a notable maximum in the right-entrance quadrant of both anticyclonic and linear jet streaks. Finally, it was found that the upper-level divergence and vertical velocity in all jet-quadrants have a tendency to decrease as jet streak directions shift from SSW to NNW.

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The Dynamic and Thermodynamic Structures Associated with a Series of Heavy Precipitation Events over China during January 2008

Weather and Forecasting ◽

10.1175/2010waf2222335.1 ◽

2010 ◽

Vol 25 (4) ◽

pp. 1124-1141 ◽

Cited By ~ 16

Author(s):

Xiaohui Shi ◽

Xiangde Xu ◽

Chungu Lu

Keyword(s):

Large Scale ◽

East Coast ◽

Heavy Precipitation ◽

Chinese History ◽

Physical Processes ◽

Ice Storms ◽

Upper Level ◽

Upper Level Jet ◽

The Western Pacific ◽

Precipitation Events

Abstract In the winter of 2008, China experienced once-in-50-yr (or once in 100 yr for some regions) snow and ice storms. These storms brought huge socio economical impacts upon the Chinese people and government. Although the storms had been predicted, their severity and persistence were largely underestimated. In this study, these cases were revisited and comprehensive analyses of the storms’ dynamic and thermodynamic structures were conducted. These snowstorms were also compared with U.S. east coast snowstorms. The results from this study will provide insights on how to improve forecasts for these kinds of snowstorms. The analyses demonstrated that the storms exhibited classic patterns of large-scale circulation common to these types of snowstorms. However, several physical processes were found to be unique and thought to have played crucial roles in intensifying and prolonging China’s great snowstorms of 2008. These include a subtropical high over the western Pacific, an upper-level jet stream, and temperature and moisture inversions. The combined effects of these dynamic and thermodynamic structures are responsible for the development of the storms into one of the most disastrous events in Chinese history.

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Association of the Poleward Shift of East Asian Subtropical Upper-Level Jet with Frequent Tropical Cyclone Activities over the Western North Pacific in Summer

Journal of Climate ◽

10.1175/jcli-d-16-0334.1 ◽

2017 ◽

Vol 30 (14) ◽

pp. 5597-5603 ◽

Cited By ~ 6

Author(s):

Xian Chen ◽

Zhong Zhong ◽

Wei Lu

Keyword(s):

Tropical Cyclone ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

East Asian ◽

Teleconnection Pattern ◽

Reanalysis Dataset ◽

Poleward Shift ◽

Upper Level ◽

Upper Level Jet

The NCEP–NCAR reanalysis dataset and the tropical cyclone (TC) best-track dataset from the Regional Specialized Meteorological Center (RSMC) Tokyo Typhoon Center were employed in the present study to investigate the possible linkage of the meridional displacement of the East Asian subtropical upper-level jet (EASJ) with the TC activity over the western North Pacific (WNP). Results indicate that summertime frequent TC activities would create the poleward shift of the EASJ through a stimulated Pacific–Japan (PJ) teleconnection pattern as well as the changed large-scale meridional temperature gradient. On the contrary, in the inactive TC years, the EASJ is often located more southward than normal with an enhanced intensity. Therefore, TC activities over the WNP are closely related to the location and intensity of the EASJ in summer at the interannual time scale.

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Polar Winds: Airborne Doppler Wind Lidar Missions in the Arctic for Atmospheric Observations and Numerical Model Comparisons

Atmosphere ◽

10.3390/atmos11111141 ◽

2020 ◽

Vol 11 (11) ◽

pp. 1141

Author(s):

Steven Greco ◽

George D. Emmitt ◽

Alice DuVivier ◽

Keith Hines ◽

Michael Kavaya

Keyword(s):

Wrf Model ◽

The Arctic ◽

Weather Research And Forecasting ◽

Dynamic Features ◽

Wind Retrieval ◽

Atmospheric Observations ◽

Wind Lidar ◽

Upper Level ◽

Upper Level Jet ◽

Doppler Wind Lidar

During October–November 2014 and May 2015, NASA sponsored and conducted a pair of airborne campaigns called Polar Winds to investigate atmospheric circulations, particularly in the boundary layer, over the Arctic using NASA’s Doppler Aerosol WiNd (DAWN) lidar. A description of the campaigns, the DAWN instrument, wind retrieval methods and data processing is provided. During the campaigns, the DAWN instrument faced backscatter sensitivity issues in the low aerosol conditions that were fairly frequent in the 2–6 km altitude range. However, when DAWN was able to make measurements, comparisons with dropsondes show good agreement and very low bias and supports the use of an airborne Doppler wind lidar such as DAWN that can provide profiles with high velocity precision, ~65 m vertical resolution and horizontal spacing as fine as 3–7 km. Case study analyses of a Greenland tip jet, barrier winds and an upper level jet are presented and show how, despite sensitivity issues, DAWN data can be confidently used in diagnostic studies of dynamic features in the Arctic. Comparisons with both an operational and research Weather Research and Forecasting (WRF) model for these events also show the potential for utilization in model validation. The sensitivity issues of the DAWN laser have since been corrected.

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Hybrid Mass Coordinate in WRF-ARW and Its Impact on Upper-Level Turbulence Forecasting

Monthly Weather Review ◽

10.1175/mwr-d-18-0334.1 ◽

2019 ◽

Vol 147 (3) ◽

pp. 971-985 ◽

Cited By ~ 4

Author(s):

Sang-Hun Park ◽

Joseph B. Klemp ◽

Jung-Hoon Kim

Keyword(s):

Wrf Model ◽

Real Data ◽

Artificial Noise ◽

Test Case ◽

Surface Boundary ◽

Vertical Coordinate ◽

Numerical Errors ◽

Mountainous Regions ◽

Upper Level ◽

Upper Level Jet

Abstract Although a terrain-following vertical coordinate is well suited for the application of surface boundary conditions, it is well known that the influences of the terrain on the coordinate surfaces can contribute to increase numerical errors, particularly over steep topography. To reduce these errors, a hybrid sigma–pressure coordinate is formulated in the Weather Research and Forecasting (WRF) Model, and its effects are illustrated for both an idealized test case and a real-data forecast for upper-level turbulence. The idealized test case confirms that with the basic sigma coordinate, significant upper-level disturbances can be produced due to numerical errors that arise as the advection of strong horizontal flow is computed along coordinate surfaces that are perturbed by smaller-scale terrain influences. With the hybrid coordinate, this artificial noise is largely eliminated as the mid- and upper-level coordinate surfaces correspond much more closely to constant pressure surfaces. In real-data simulations for upper-level turbulence forecasting, the WRF Model using the basic sigma coordinate tends to overpredict the strength of upper-air turbulence over mountainous regions because of numerical errors arising as a strong upper-level jet is advected along irregular coordinate surfaces. With the hybrid coordinate, these errors are reduced, resulting in an improved forecast of upper-level turbulence. Analysis of kinetic energy spectra for these simulations confirms that artificial amplitudes in the smaller scales at upper levels that arise with the basic sigma coordinate are effectively removed when the hybrid coordinate is used.

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A Climatology of the Structure, Evolution, and Propagation of Midlatitude Cyclones in the Southeast United States

Journal of Climate ◽

10.1175/jcli-d-12-00657.1 ◽

2013 ◽

Vol 26 (21) ◽

pp. 8406-8421 ◽

Cited By ~ 10

Author(s):

Rosana Nieto Ferreira ◽

Linwood Hall ◽

Thomas M. Rickenbach

Keyword(s):

United States ◽

Level Structure ◽

Windward Side ◽

Structure Evolution ◽

Pressure Center ◽

Southeast United States ◽

Upper Level ◽

Upper Level Jet ◽

North Latitude ◽

Midlatitude Cyclones

Abstract The seasonal and interannual variability of the structure, evolution, and propagation of midlatitude cyclones in the southeast United States are studied using a composite analysis. In the upper levels, the composites show that the axis of the wintertime upper-level trough remains north–south oriented and propagates eastward along 40°N, while the summertime upper-level trough has a much slower propagation at a farther north latitude and an axis that is tilted in the northeast–southwest direction. Upper-level circulation changes are consistent with a shift from wintertime “cyclonic behavior” to summertime “anticyclonic behavior” midlatitude cyclones. Significant changes in the low-level structure and precipitation patterns of midlatitude cyclones ensue from these upper-level changes. While the winter composite is characterized by eastward-propagating midlatitude cyclones that extend deep into the subtropics, the summer composite is characterized by semistationary midlatitude troughs that only briefly skirt the subtropics. Wintertime precipitation occurs only in and ahead of the surface low pressure center, whereas summertime precipitation occurs in all days of the composite. As a result, over 70% (30%) of wintertime (summertime) precipitation in the Carolinas occurs on days when midlatitude cyclones are present. The wintertime composites also show that midlatitude cyclones produce more precipitation on the windward side of the Appalachians than over the Carolinas, suggesting a rain shadow effect of the mountains. The ENSO-related variability of the structure, evolution, and propagation of midlatitude cyclones shows the presence of a more intense and southward-displaced upper-level jet, stronger midlatitude cyclones, and more intense precipitation over a larger area during El Niño than La Niña or normal years.

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