scholarly journals Analysis of a Progressive Derecho Climatology and Associated Formation Environments

2016 ◽  
Vol 144 (4) ◽  
pp. 1363-1382 ◽  
Author(s):  
Corey T. Guastini ◽  
Lance F. Bosart
Keyword(s):  
Marked Decrease ◽  
Appalachian Mountains ◽  
Warm Season ◽  
Rocky Mountain ◽  
Low Level ◽  
The North ◽  
The Common ◽  
Upper Level ◽  
Upper Level Jet ◽  
The Relationship

Abstract A 1996–2013 May–August U.S. progressive derecho climatology existing entirely within the modern radar era is constructed identifying 256 derecho events over the 18-yr span. A corridor of enhanced derecho activity in agreement with previous derecho studies stretches from southern Minnesota to the border of Ohio and West Virginia with a marked decrease east of the Appalachian Mountains. A secondary maximum in progressive derecho activity exists in Kansas and Oklahoma. Analyses of derecho frequency by month of the warm season indicate a northward shift in frequency through July and an increase in derecho frequency through the first half of the warm season followed by a large decrease in August. The 256 identified derecho events are divided subjectively into seven distinct categories based on the synoptic environments in which they form. While the prevailing “northwest flow” conceptual model is upheld as the dominant progressive derecho synoptic category, the common occurrence of warm-season progressive derechos ahead of well-defined upper-level troughs is presented. This connection between upper-level troughs and progressive derecho formation expands on the relationship between upper-level troughs and serial derecho formation that has been the focus of past studies. In addition, a link between progressive derecho formation and easterly low-level flow to the north of a Rocky Mountain lee cyclone is bolstered. Consistent with previous derecho studies, all composite categories are characterized by large low-level moisture and the presence of an upper-level jet at derecho initiation.

scholarly journals Investigation of Atmospheric Rivers Impacting the Pigeon River Basin of the Southern Appalachian Mountains

2018 ◽  
Vol 33 (1) ◽  
pp. 283-299 ◽  
Author(s):  
Douglas K. Miller ◽  
David Hotz ◽  
Jessica Winton ◽  
Lukas Stewart
Keyword(s):  
North Carolina ◽  
River Basin ◽  
Large Scale ◽  
Large Fraction ◽  
Appalachian Mountains ◽  
Warm Season ◽  
Atmospheric Rivers ◽  
Southern Appalachian Mountains ◽  
Low Level ◽  
Southern Appalachian

Abstract Rainfall observations in the Pigeon River basin of the southern Appalachian Mountains over a 5-yr period (2009–14) are examined to investigate the synoptic patterns responsible for downstream flooding events as observed near Knoxville, Tennessee, and Asheville, North Carolina. The study is designed to address the hypothesis that atmospheric rivers (ARs) are primarily responsible for the highest accumulation periods observed by the gauge network and that these periods correspond to events having a societal hazard (flooding). The upper 2.5% (extreme) and middle 33% (normal) rainfall events flagged using the gauge network observations showed that half of the heaviest rainfall cases were associated with an AR. Of those extreme events having an AR influence, over 73% had a societal hazard defined as minor-to-major flooding at the USGS river gauge located in Newport, Tennessee, or flooding observations for locations near the Tennessee and North Carolina border reported in the Storm Data publication. Composites of extreme AR-influenced events revealed a synoptic pattern consisting of a highly amplified slow-moving positively tilted trough, suggestive of the anticyclonic Rossby wave breaking scenario that sometimes precedes hydrological events of high impact. Composites of extreme non-AR events indicated a large-scale weather pattern typical of a warm season scenario in which an anomalous low-level cyclone, cut off far from the primary upper-tropospheric jet, was located in the southeastern United States. AR events without a societal hazard represented a large fraction (75%–88%) of all ARs detected during the study period. Synoptic-scale weather patterns of these events were fast moving and had weak low-level atmospheric dynamics.

scholarly journals A Climatology of Subtropical Cyclones in the South Atlantic

2012 ◽  
Vol 25 (21) ◽  
pp. 7328-7340 ◽  
Author(s):  
Jenni L. Evans ◽  
Aviva Braun
Keyword(s):  
North Atlantic ◽  
Warm Season ◽  
Hybrid Structure ◽  
South Atlantic ◽  
The South ◽  
Rossby Wave Breaking ◽  
The North ◽  
Brazil Current ◽  
Eastern Australia ◽  
Upper Level

A 50-yr climatology (1957–2007) of subtropical cyclones (STs) in the South Atlantic is developed and analyzed. A subtropical cyclone is a hybrid structure (upper-level cold core and lower-level warm core) with associated surface gale-force winds. The tendency for warm season development of North Atlantic STs has resulted in these systems being confused as tropical cyclones (TCs). In fact, North Atlantic STs are a regular source of the incipient vortices leading to North Atlantic TC genesis. In 2004, Hurricane Catarina developed in the South Atlantic and made landfall in Brazil. A TC system had been previously unobserved in the South Atlantic, so the incidence of Catarina highlighted the lack of an ST climatology for the region to provide a context for the likelihood of future systems. Sixty-three South Atlantic STs are documented over the 50-yr period analyzed in this climatology. In contrast to the North Atlantic, South Atlantic STs occur relatively uniformly throughout the year; however, their preferred location of genesis and mechanisms for this genesis do exhibit some seasonal variability. Rossby wave breaking was identified as the mechanism for the ST vortex initiation for North Atlantic STs. A subset of South Atlantic STs forms via this mechanism, however, an additional mechanism for ST genesis is identified here: lee cyclogenesis downstream of the Andes in the Brazil Current region—an area favorable for convection. This formation mechanism is similar to development of type-2 east coast lows in the Tasman Sea off eastern Australia.

Simulations of the 2004 North American Monsoon: NAMAP2

2009 ◽  
Vol 22 (24) ◽  
pp. 6716-6740 ◽  
Author(s):  
D. S. Gutzler ◽  
L. N. Long ◽  
J. Schemm ◽  
S. Baidya Roy ◽  
M. Bosilovich ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
North American ◽  
Warm Season ◽  
North American Monsoon ◽  
Regional Models ◽  
Global Models ◽  
Low Level ◽  
The Core ◽  
The North ◽  
Low Level Jet

Abstract The second phase of the North American Monsoon Experiment (NAME) Model Assessment Project (NAMAP2) was carried out to provide a coordinated set of simulations from global and regional models of the 2004 warm season across the North American monsoon domain. This project follows an earlier assessment, called NAMAP, that preceded the 2004 field season of the North American Monsoon Experiment. Six global and four regional models are all forced with prescribed, time-varying ocean surface temperatures. Metrics for model simulation of warm season precipitation processes developed in NAMAP are examined that pertain to the seasonal progression and diurnal cycle of precipitation, monsoon onset, surface turbulent fluxes, and simulation of the low-level jet circulation over the Gulf of California. Assessment of the metrics is shown to be limited by continuing uncertainties in spatially averaged observations, demonstrating that modeling and observational analysis capabilities need to be developed concurrently. Simulations of the core subregion (CORE) of monsoonal precipitation in global models have improved since NAMAP, despite the lack of a proper low-level jet circulation in these simulations. Some regional models run at higher resolution still exhibit the tendency observed in NAMAP to overestimate precipitation in the CORE subregion; this is shown to involve both convective and resolved components of the total precipitation. The variability of precipitation in the Arizona/New Mexico (AZNM) subregion is simulated much better by the regional models compared with the global models, illustrating the importance of transient circulation anomalies (prescribed as lateral boundary conditions) for simulating precipitation in the northern part of the monsoon domain. This suggests that seasonal predictability derivable from lower boundary conditions may be limited in the AZNM subregion.

Objective Categorization of Heavy-Rain-Producing MCS Synoptic Types by Rotated Principal Component Analysis

2014 ◽  
Vol 142 (5) ◽  
pp. 1716-1737 ◽  
Author(s):  
John M. Peters ◽  
Russ S. Schumacher
Keyword(s):  
Principal Component Analysis ◽  
Temperature Gradient ◽  
Potential Temperature ◽  
Warm Season ◽  
Principal Component ◽  
Heavy Rain ◽  
Component Analysis ◽  
Synoptic Type ◽  
Low Level ◽  
Upper Level

Abstract In this research, rotated principal component analysis was applied to the atmospheric fields associated with a large sample of heavy-rain-producing mesoscale convective systems (MCSs). Cluster analysis in the subspace defined by the leading two resulting principal components revealed two subtypes with distinct synoptic and mesoscale characteristics, which are referred to as warm-season-type and synoptic-type events, respectively. Subsequent composite analysis showed that both subtypes typically occurred on the cool side of a quasi-stationary, low-level frontal boundary, within a region of locally maximized low-level convergence and warm advection. Synoptic-type events, which tended to exhibit greater horizontal extent than warm-season-type events, typically occurred downstream of a progressive upper-level trough, along a low-level potential temperature gradient with the warmest air to the south and southeast. Warm-season-type events, on the other hand, occurred within the right-entrance region of a minimally to anticyclonically curved upper-level jet streak, along a low-level potential temperature gradient with the warmest low-level air to the southwest. Synoptic-scale forcing for ascent was stronger in synoptic-type events, while low-level moisture was greater in warm-season-type events. Warm-season-type events were frequently preceded by the passage of a trailing-stratiform- (TS) type MCS, whereas synoptic-type events often occurred prior to the passage of a TS-type system. Analysis of the composite vertical wind profiles at the event location suggests that quasi-stationary behavior in warm-season events predominantly resulted from upstream propagation that nearly canceled advection by the mean steering flow, whereas in the case of synoptic-type events training predominantly resulted from system motion that paralleled a front.

SST fronts along the Gulf Stream and Kuroshio affect the atmospheric winter climatology primarily in the absence of storms

2021 ◽  
Author(s):  
Thomas Spengler ◽  
Leonidas Tsopouridis ◽  
Clemens Spensberger
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Storm Track ◽  
Heat Fluxes ◽  
Cyclone Activity ◽  
Surface Heat Fluxes ◽  
The North ◽  
Upper Level ◽  
Upper Level Jet ◽  
Kuroshio Region

<p>The Gulf Stream and Kuroshio regions feature strong sea surface temperature (SST) gradients that influence cyclone development and the storm track. Smoothing the SSTs in either the North Atlantic or North Pacific has been shown to yield a reduction in cyclone activity, surface heat fluxes, and precipitation, as well as a southward shift of the storm track and the upper-level jet. To what extent these changes are attributable to changes in individual cyclone behaviour, however, remains unclear. Comparing simulations with realistic and smoothed SSTs in the atmospheric general circulation model AFES, we find that the intensification of individual cyclones in the Gulf Stream or Kuroshio region is only marginally affected by reducing the SST gradient. In contrast, we observe considerable changes in the climatological mean state, with a reduced cyclone activity in the North Atlantic and North Pacific storm tracks that are also shifted equator-ward in both basins. The upper-level jet in the Atlantic also shifts equator-ward, while the jet in the Pacific strengthens in its climatological position and extends further east. Surface heat fluxes, specific humidity, and precipitation also respond strongly to the smoothing of the SST, with a considerable decrease of their mean values on the warm side of the SST front. This decrease is more pronounced in the Gulf Stream than in the Kuroshio region, due to the amplified decrease in SST along the Gulf Stream SST front.  Considering the pertinent variables occurring within different radii of cyclones in each basin over their entire lifetime, we find cyclones to play only a secondary role in explaining the mean states differences between smoothed and realistic SST experiments.</p>

Driving mechanisms of South Atlantic storm track changes in an extreme climate scenario according to HadGEM2-ES and WRF downscaling

2021 ◽  
Author(s):  
Carolina Gramcianinov ◽  
Ricardo de Camargo ◽  
Pedro Silva Dias
Keyword(s):  
Storm Track ◽  
Static Stability ◽  
South Atlantic ◽  
Brazilian Coast ◽  
The South ◽  
La Plata ◽  
Low Level ◽  
Upper Level ◽  
Upper Level Jet ◽  
Projected Changes

<p>This work aims to assess the future projected changes in the cyclones originated in the South Atlantic, focusing on their genesis and intensifying mechanisms. The TRACK program was used to identify and track cyclones based on the relative vorticity from winds at 850 hPa. Spatial distribution maps of the atmospheric environment at the time of genesis were built using information sampled from individual features, e.g., mean upper-level jet speed, low-level moisture transport. First, we evaluated the HadGEM2-ES ability to reproduce the main characteristics of the South Atlantic cyclones and access their future projected changes using the RCP8.5 scenario. Then, we performed a dynamical downscaling using the WRF model to improve the resolution of the climate model in the historical (ExpHad-HIST) and RCP8.5 (ExpHad-RCP85) scenarios. Our results showed that HadGEM2-ES were able to reproduce the South Atlantic storm track pattern and its four main cyclogenesis regions: (1) Southern Brazilian coast (SE-BR, 30ºS); (2) Northern Argentina, Uruguay, and Southern Brazil (LA PLATA, 35ºS); (3) central coast of Argentina (ARG, 40ºS-55º) and; (4) Southeastern South Atlantic (SE-SAO, 55ºS and 10ºW). However, HadGEM-ES presented less intense cyclones and a negative density bias on the subtropical storm track, as a consequence of an underestimated genesis in the LA PLATA and SE-BR regions. The ExpHad-HIST provided a better representation of these two genesis regions, where the effects of an improved orography, mesoscale processes and strong and more organized low-level jet seem to reduce the static stability and support cyclone development. HadGEM2-ES RCP8.5 future projection showed a decrease of 10% in the number of cyclones over South Atlantic and a poleward shift of the main storm track, linked to the larger reduction of systems in mid than high latitudes. This increase in the cyclone activity at 30ºS led to the high track density in the South Atlantic subtropical storm track, both in the summer and winter. The ExpHad-RCP85 also showed a poleward shift of the main storm track, but mainly in the summer. The reduction and southward displacement of the cyclone occurrences can be addressed to the increase in the static stability at mid-latitudes. However, the increase in the moisture content at low levels seems to balance the effect of the static stability as long as there is an increase in the genesis in the equatorward genesis regions. In fact, the ExpHad-RCP85 simulated growth in the genesis in the northern edge of SE-BR (20ºS, 50ºW) and ARG (45ºS) regions, in the summer, and the LA PLATA region in the winter - being the last change also observed in HadGEM2-ES RCP8.5. The large increase in the low-level moisture and a strengthening of the equatorward flank of the upper-level jet could justify more genesis at these locations, competing with the increase in static stability. Moreover, the large content of low-level moisture available in the future simulation may also be connected to the observed intensification of the cyclones over the Uruguayan and Brazilian coast.</p>

scholarly journals Appearance of the common paper nautilus Argonauta argo related to the increase of the sea surface temperature in the north-eastern Atlantic

2002 ◽  
Vol 82 (5) ◽  
pp. 855-858 ◽  
Author(s):  
A. Guerra ◽  
A.F. González ◽  
F. Rocha
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
First Record ◽  
Mature Female ◽  
Sea Surface ◽  
North West ◽  
The North ◽  
North Eastern ◽  
The Common ◽  
The Relationship

The relationship between the increase of the sea surface temperature observed off the Galician coast and the appearance of a tropical poikilotherm species Argonauta argo in these coasts is discussed. This is the first record of Argonautaargo in the north-west Iberian Peninsula. A female of this species was captured alive near the surface at dusk on 22 December 2000 in the Ria de Aldán (42°15′N–08°48′W). The specimen, a mature female of 70 mm mantle length and 96 mm shell diameter, died 36 hours after introduction in the tank.

The status of Salterella as a Lower Cambrian index fossil

1988 ◽  
Vol 25 (3) ◽  
pp. 403-416 ◽  
Author(s):  
W. H. Fritz ◽  
Ellis L. Yochelson
Keyword(s):  
North America ◽  
Lower Cambrian ◽  
Appalachian Mountains ◽  
Early Cambrian ◽  
Medial Part ◽  
North American Cordillera ◽  
The North ◽  
Superficial Resemblance ◽  
The Status ◽  
The Relationship

In the North American Cordillera there is strong evidence that Salterella is restricted to the medial part of the Bonnia–Olenellus Zone. Reported younger and older occurrences are attributed to either stratigraphic error or misidentification. An unnamed genus with a superficial resemblance immediately postdates Salterella, but it lacks an inner laminar cone. In the Cordillera Salterella occurs in inner detrital and middle carbonate belt strata that were deposited in the upper half of Grand Cycle B and the lower half of Grand Cycle C.In and near the Appalachian Mountains of North America and in Greenland, Spitsbergen, and Scotland, occurrences of Salterella are consistent with a medial Bonnia–Olenellus Zone age; however, this cannot be as rigorously tested as in the Cordillera, because of fewer taxa associated with the genus and in super- and subjacent strata. Outer detrital (basinal) strata of the Taconic Allochthon contain Salterella, but it is uncertain whether the fossils are of local or derived origin.Speculations that Campitius titanius Firby and Durham of California belongs in the genus Salterella are doubtful, and C. titanius is clearly older. The relationship between Salterella and Volborthella and their relative ages within the Early Cambrian are still unclear.

scholarly journals The Next-Generation Goddard Convective–Stratiform Heating Algorithm: New Tropical and Warm-Season Retrievals for GPM

2018 ◽  
Vol 31 (15) ◽  
pp. 5997-6026 ◽  
Author(s):  
Stephen E. Lang ◽  
Wei-Kuo Tao
Keyword(s):  
Warm Season ◽  
Tropical Rainfall Measuring Mission ◽  
Shallow Convection ◽  
Heating Rates ◽  
Low Level ◽  
Precipitation Measurement ◽  
Cloud Resolving Model ◽  
Upper Level ◽  
Heating Profiles ◽  
Global Precipitation

The Goddard convective–stratiform heating (CSH) algorithm, used to estimate cloud heating in support of the Tropical Rainfall Measuring Mission (TRMM), is upgraded in support of the Global Precipitation Measurement (GPM) mission. The algorithm’s lookup tables (LUTs) are revised using new and additional cloud-resolving model (CRM) simulations from the Goddard Cumulus Ensemble (GCE) model, producing smoother heating patterns that span a wider range of intensities because of the increased sampling and finer GPM product grid. Low-level stratiform cooling rates are reduced in the land LUTs for a given rain intensity because of the rain evaporation correction in the new four-class ice (4ICE) scheme. Additional criteria, namely, echo-top heights and low-level reflectivity gradients, are tested for the selection of heating profiles. Those resulting LUTs show greater and more precise variation in their depth of heating as well as a tendency for stronger cooling and heating rates when low-level dB Z values decrease toward the surface. Comparisons versus TRMM for a 3-month period show much more low-level heating in the GPM retrievals because of increased detection of shallow convection, while upper-level heating patterns remain similar. The use of echo tops and low-level reflectivity gradients greatly reduces midlevel heating from ~2 to 5 km in the mean GPM heating profile, resulting in a more top-heavy profile like TRMM versus a more bottom-heavy profile with much more midlevel heating. Integrated latent heating rates are much better balanced versus surface rainfall for the GPM retrievals using the additional selection criteria with an overall bias of +4.3%.

scholarly journals On the Relationship between Spring NAO and Snowmelt in the Upper Southwestern United States

2017 ◽  
Vol 30 (14) ◽  
pp. 5141-5149 ◽  
Author(s):  
Boksoon Myoung ◽  
Seung Hee Kim ◽  
Jinwon Kim ◽  
Menas C. Kafatos
Keyword(s):  
United States ◽  
Southern Oscillation ◽  
Warm Season ◽  
Weather Conditions ◽  
Underlying Mechanism ◽  
The United States ◽  
The North ◽  
The North Atlantic Oscillation ◽  
The Relationship ◽  
Spring Snowmelt

This study examines the relationship between the North Atlantic Oscillation (NAO) and snowmelt in spring in the upper southwestern states of the United States (UP_SW) including California, Nevada, Utah, and Colorado, using SNOTEL datasets for 34 yr (1980–2014). Statistically significant negative correlations are found between NAO averages in the snowmelt period and timings of snowmelt (i.e., positive NAO phases in spring enhance snowmelt, and vice versa). It is also found that correlations between El Niño–Southern Oscillation and snowmelt are negligible in the region. The NAO–snowmelt relationship is most pronounced below the 2800-m level; above this level, the relationship becomes weaker. The underlying mechanism for this link is that a positioning of upper-tropospheric anticyclonic (cyclonic) circulations over the western United States that are associated with development of the positive (negative) NAO phases tends to bring warmer and drier (colder and wetter) spring weather conditions to the region. The temperature variations related with the NAO phases also strongly modulate the snowfall–rainfall partitioning. The relationship between the NAO and spring snowmelt can serve as key information for the warm season water resources management in the UP_SW.

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