scholarly journals Climatology of Barrier Jets along the Alaskan Coast. Part II: Large-Scale and Sounding Composites

2006 ◽  
Vol 134 (2) ◽  
pp. 454-477 ◽  
Author(s):  
Brian A. Colle ◽  
Kenneth A. Loescher ◽  
George S. Young ◽  
Nathaniel S. Winstead
Keyword(s):  
Large Scale ◽  
Warm Season ◽  
Yukon Territory ◽  
The Other ◽  
Cool Season ◽  
Low Level ◽  
Alaskan Coast ◽  
Sar Imagery ◽  
Upper Level ◽  
Barrier Jets

Abstract This paper investigates the large-scale flow and thermodynamic structures associated with barrier jets along the Alaskan coast using the National Centers for Environmental Prediction (NCEP) reanalysis, as well as the average wind, moisture, and thermodynamic soundings at Yakutat, Alaska (YAK), and Whitehorse, Yukon Territory, Canada (YXY). Large-scale and sounding composites are constructed for all barrier jets objectively identified around YAK using synthetic aperture radar (SAR) imagery during the cool and warm seasons of 1998–2003. During the cool season the jet events are separated into those with sharp upstream wind gradients (shock jets), highly variable (“gustlike”) surface winds (variable jets), and the other jet events (other jets). Those cool season barrier jets without shock or variable characteristics are associated with an anomalously deep upper-level trough approaching the Gulf of Alaska and an anomalous ridge over western Canada and interior Alaska. The associated surface cyclone and surface ridging result in strong low-level southerlies over southeast Alaska and the advection of 850-mb warm anomalies northward from the subtropics to Alaska. In contrast, the shock events have significant cold anomalies at 850 mb over the interior, while both the shock and variable jets have less upper-level ridging over the interior. The warm season other-jet composite is similar to that for the cool season, except that an 850-mb cool anomaly develops near the coast and the approaching upper-level trough is not significantly deeper than climatology. The sounding composite at YAK of the other-jet type during the cool season is more stable, moist, and slightly cooler at lower levels than the nonjet events. The largest low-level cool, dry, and high stability anomalies are for the shock events at YAK and YXY, which suggests that this cold and dry air source over the interior is an important ingredient for the development of sharp frontlike boundaries to the barrier jet. In contrast, the variable jets have weaker low-level stability, which favors the subsequent mixing of higher momentum to the surface in localized areas. The warm season jets also have cooler lower levels than those for the nonjet events, but the lower levels are nearly well mixed with little stratification, especially over the interior.

Teleconnections Governing the Interannual Variability of Great Plains Low-Level Jets in May

2021 ◽  
pp. 1-60
Author(s):  
Shubhi Agrawal ◽  
Craig R. Ferguson ◽  
Lance Bosart ◽  
D. Alex Burrows
Keyword(s):  
Interannual Variability ◽  
Great Plains ◽  
Large Scale ◽  
Warm Season ◽  
Near Surface ◽  
Low Level ◽  
South Central ◽  
Decadal Scale ◽  
Low Level Jets ◽  
Upper Level

AbstractA spectral analysis of Great Plains 850-hPa meridional winds (V850) from ECMWF’s coupled climate reanalysis of 1901-2010 (CERA-20C) reveals that their warm season (April-September) interannual variability peaks in May with 2-6 year periodicity, suggestive of an underlying teleconnection influence on low-level jets (LLJs). Using an objective, dynamical jet classification framework based on 500-hPa wave activity, we pursue a large scale teleconnection hypothesis separately for LLJs that are uncoupled (LLJUC) and coupled (LLJC) to the upper-level jet stream. Differentiating between jet types enables isolation of their respective sources of variability. In the South Central Plains (SCP), May LLJCs account for nearly 1.6 times more precipitation and 1.5 times greater V850 compared to LLJUCs. Composite analyses of May 250-hPa geopotential height (Z250) conditioned on LLJC and LLJUC frequencies highlight a distinct planetary-scale Rossby wave pattern with wavenumber-five, indicative of an underlying Circumglobal Teleconnection (CGT). An index of May CGT is found to be significantly correlated with both LLJC (r = 0.62) and LLJUC (r = −0.48) frequencies. Additionally, a significant correlation is found between May LLJUC frequency and NAO (r = 0.33). Further analyses expose decadal scale variations in the CGT-LLJC(LLJUC) teleconnection that are linked to the PDO. Dynamically, these large scale teleconnections impact LLJ class frequency and intensity via upper-level geopotential anomalies over the western U.S. that modulate near-surface geopotential and temperature gradients across the SCP.

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 Drought Relief and Reversal over North America from 1500 to 2016

2021 ◽  
Vol 25 (1) ◽  
pp. 94-107
Author(s):  
M. C. A. Torbenson ◽  
D. W. Stahle ◽  
I. M. Howard ◽  
D. J. Burnette ◽  
D. Griffin ◽  
...  
Keyword(s):  
Soil Moisture ◽  
North America ◽  
Land Surface ◽  
Large Scale ◽  
Temporal Stability ◽  
Warm Season ◽  
Cool Season ◽  
Continental Scale ◽  
The North ◽  
Drought Relief

Abstract Season-to-season persistence of soil moisture drought varies across North America. Such interseasonal autocorrelation can have modest skill in forecasting future conditions several months in advance. Because robust instrumental observations of precipitation span less than 100 years, the temporal stability of the relationship between seasonal moisture anomalies is uncertain. The North American Seasonal Precipitation Atlas (NASPA) is a gridded network of separately reconstructed cool-season (December–April) and warm-season (May–July) precipitation series and offers new insights on the intra-annual changes in drought for up to 2000 years. Here, the NASPA precipitation reconstructions are rescaled to represent the long-term soil moisture balance during the cool season and 3-month-long atmospheric moisture during the warm season. These rescaled seasonal reconstructions are then used to quantify the frequency, magnitude, and spatial extent of cool-season drought that was relieved or reversed during the following summer months. The adjusted seasonal reconstructions reproduce the general patterns of large-scale drought amelioration and termination in the instrumental record during the twentieth century and are used to estimate relief and reversals for the most skillfully reconstructed past 500 years. Subcontinental-to-continental-scale reversals of cool-season drought in the following warm season have been rare, but the reconstructions display periods prior to the instrumental data of increased reversal probabilities for the mid-Atlantic region and the U.S. Southwest. Drought relief at the continental scale may arise in part from macroscale ocean–atmosphere processes, whereas the smaller-scale regional reversals may reflect land surface feedbacks and stochastic variability.

Welcome to the C4 World

2000 ◽  
Vol 6 ◽  
pp. 273-286 ◽  
Author(s):  
Thure E. Cerling ◽  
James R. Ehleringer
Keyword(s):  
Primary Productivity ◽  
Net Primary Productivity ◽  
Warm Season ◽  
The Other ◽  
Cool Season ◽  
Carbon Compound ◽  
Low Latitudes ◽  
The World ◽  
History Of ◽  
Recent Origin

There are two principal mechanisms of photosynthesis amongst the plants of the world. One produces a 3-carbon compound as the primary photosynthate and is called C3 photosynthesis. The other produces a 4-carbon compound as its primary photosynthate and is called C4 photosynthesis. This latter method is of rather recent origin, and its inception had important consequences for the flora and fauna of the world. The C4 plants make up a significant portion of global net primary productivity, especially in low latitudes. C4 plants are predominantly warm-season grasses, while C3 plants include most dicotyledons and cool-season monocotyledons. In this review we answer the questions about how C4 photosynthesis differs from C3 photosynthesis, where C4 plants are found, and review the paleoecological history of C4 photosynthesis.

scholarly journals Sensitivity of Cloud-Resolving Simulations of Warm-Season Convection to Cloud Microphysics Parameterizations

2007 ◽  
Vol 135 (8) ◽  
pp. 2854-2868 ◽  
Author(s):  
Changhai Liu ◽  
Mitchell W. Moncrieff
Keyword(s):  
Large Scale ◽  
Prediction Models ◽  
Weather Prediction ◽  
Warm Season ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
Fine Grid ◽  
Upper Level ◽  
Heating Profiles ◽  
Microphysical Parameterization

Abstract This paper investigates the effects of cloud microphysics parameterizations on simulations of warm-season precipitation at convection-permitting grid spacing. The objective is to assess the sensitivity of summertime convection predictions to the bulk microphysics parameterizations (BMPs) at fine-grid spacings applicable to the next generation of operational numerical weather prediction models. Four microphysical parameterization schemes are compared: simple ice (Dudhia), four-class mixed phase (Reisner et al.), Goddard five-class mixed phase (Tao and Simpson), and five-class mixed phase with graupel (Reisner et al.). The experimentation involves a 7-day episode (3–9 July 2003) of U.S. midsummer convection under moderate large-scale forcing. Overall, the precipitation coherency manifested as eastward-moving organized convection in the lee of the Rockies is insensitive to the choice of the microphysics schemes, and the latent heating profiles are also largely comparable among the BMPs. The upper-level condensate and cloudiness, upper-level radiative cooling/heating, and rainfall spectrum are the most sensitive, whereas the domain-mean rainfall rate and areal coverage display moderate sensitivity. Overall, the three mixed-phase schemes outperform the simple ice scheme, but a general conclusion about the degree of sophistication in the microphysics treatment and the performance is not achievable.

The impacts of ENSO and PNA teleconnections on upper-level coupling to the Great Plains low-level jet

2020 ◽  
Author(s):  
D. Alex Burrows ◽  
Craig Ferguson ◽  
Shubhi Agrawal ◽  
Lance Bosart
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
The United States ◽  
Jet Stream ◽  
Central Pacific ◽  
Frequency Distributions ◽  
Low Level ◽  
Enso Events ◽  
Low Level Jet ◽  
Upper Level

<p>The United States (U.S.) Great Plains southerly low-level jet (GPLLJ) is a ubiquitous feature of the summertime climatological flow in the central U.S. contributing to a large percentage of mean and extreme summertime rainfall, the generation of vast quantities of U.S. renewable wind energy, and severe weather outbreaks.  Like other LLJs across the globe, the GPLLJ can be 1) vertically coupled to the large-scale cyclone-anticyclone flow pattern associated with an upper-level jet stream or 2) uncoupled to the large-scale flow but sustained in response to various local land-atmosphere coupling mechanisms.  Many studies have focused on the interactions between teleconnection patterns and associated GPLLJ variability, treating the GPLLJ as a singular phenomenon.  Here, we treat the GPLLJ as two phenomena, coupled and uncoupled to the upper-level flow, and explore the multiscale impacts of SST forced and internally generated modes of variability on the GPLLJ.  With mounting evidence for the low-frequency control on higher frequency GPLLJ variability, the current study analyzes the contribution of the Pacific/North America (PNA) pattern on sub-seasonal timescales and ENSO on interannual timescales to changes in the frequency distributions of both coupled and uncoupled GPLLJs.</p><p> </p><p>This analysis utilizes 1) the Coupled ERA 20th Century (CERA-20C; 1901-2010) reanalysis from ECMWF which provides a large sample of teleconnection conditions and their impacts on GPLLJ variability and 2) a recently developed automated technique to differentiate those GPLLJs that are coupled or uncoupled to the upper-level flow.  Many studies have already shown that two distinct synoptic regimes dominate GPLLJ variability, a western U.S. trough and a central U.S. ridge.  This leads to changes in the frequency ratio of coupled and uncoupled GPLLJ events and ultimately in the location and intensity of precipitation across the GP.  Recently, Burrows et al. (2019) showed that during the Dust Bowl period of 1932-1938, the central and northern GP experienced anomalously high (low) uncoupled (coupled) GPLLJ event frequencies that coincided with a multi-year dry period across the entire region.  Understanding the upscale and lower frequency forcing patterns that lead to these distinct synoptic regimes would lead to greater predictability and forecasting skill.  On sub-seasonal timescales, it is shown that the negative phase of the PNA, which is associated with a southerly displaced Pacific jet stream and a western U.S. trough, leads to increases in the frequency of GPLLJs that are coupled to the upper-level flow, increases in Gulf of Mexico moisture flux and a redistribution of GP precipitation.  On interannual timescales, the location of ENSO events, i.e., eastern or central Pacific, is explored to determine the relationship between tropical forced variability and upper-level coupling to the GPLLJ.  In line with recent studies, it is hypothesized that central Pacific ENSO events may lead to increases in coupled GPLLJ events and precipitation, particularly in the southern GP.</p>

Joint Canada-U.S. Survey in the Mount Kennedy Region

ARCTIC ◽  
1965 ◽  
Vol 18 (2) ◽  
pp. 70
Author(s):  
Canada. Surveys and Mapping Branch
Keyword(s):  
Large Scale ◽  
Field Measurements ◽  
The United States ◽  
Geodetic Survey ◽  
Yukon Territory ◽  
Mountain Range ◽  
National Geographic Society ◽  
National Geographic ◽  
The North ◽  
Alaskan Coast

In 1935 a National Geographic Society glaciological expedition working in the St. Elias mountain range near the Alaska-Yukon Territory boundary described an unnamed mountain in the area as "magnificent, a granite peak sheathed in snow and ice on the south and west sides, and on the north and east sides has fantastic rock cliffs." Thirty years later this same peak was officially named Mount Kennedy in honour of the late President John F. Kennedy. A surge of activity in the area followed immediately. Senator Robert Kennedy climbed the mountain, an expedition sponsored by the National Geographic Society is engaged in producing a large scale map of the mountain and its environs, and a joint U.S.-Canadian party has just completed a survey through the area which will determine the precise geographic position of the mountain's summit and its elevation. The survey party was composed of six men from the United States Coast and Geodetic Survey and two men from the Surveys and Mapping Branch of the Canadian Department of Mines and Technical Surveys. The main purpose of the work was to connect existing surveys along the Alaska Highway with similar surveys along the Alaskan coast. The work will strengthen the control surveys throughout the area and provide new control points for mapping. The decision to include Mount Kennedy in the survey, while adding a touch of glamour to the operation, greatly increased the difficulties. The survey itself consists of five main stations, connected by traverse, with auxiliary points established at alternate stations to provide additional checks on field measurements. The lengths of the four traverse courses varied from eight to thirty-nine miles; the distances were measured by electronic distance measuring equipment, and the angles were measured with precise theodolites using signal lights and heliotropes for targets. ...

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.

Cyclogenesis Simulation of Typhoon Prapiroon (2000) Associated with Rossby Wave Energy Dispersion*

2010 ◽  
Vol 138 (1) ◽  
pp. 42-54 ◽  
Author(s):  
Xuyang Ge ◽  
Tim Li ◽  
Melinda S. Peng
Keyword(s):  
Rossby Wave ◽  
Wave Energy ◽  
Large Scale ◽  
Wave Train ◽  
Energy Dispersion ◽  
Sensitivity Experiment ◽  
Low Level ◽  
Filtering Technique ◽  
Upper Level

Abstract The genesis of Typhoon Prapiroon (2000), in the western North Pacific, is simulated to understand the role of Rossby wave energy dispersion of a preexisting tropical cyclone (TC) in the subsequent genesis event. Two experiments are conducted. In the control experiment (CTL), the authors retain both the previous typhoon, Typhoon Bilis, and its wave train in the initial condition. In the sensitivity experiment (EXP), the circulation of Typhoon Bilis was removed based on a spatial filtering technique of Kurihara et al., while the wave train in the wake is kept. The comparison between these two numerical simulations demonstrates that the preexisting TC impacts the subsequent TC genesis through both a direct and an indirect process. The direct process is through the conventional barotropic Rossby wave energy dispersion, which enhances the low-level wave train, the boundary layer convergence, and the convection–circulation feedback. The indirect process is through the upper-level outflow jet. The asymmetric outflow jet induces a secondary circulation with a strong divergence tendency to the left-exit side of the outflow jet. The upper-level divergence boosts large-scale ascending motion and promotes favorable environmental conditions for a TC-scale vortex development. In addition, the outflow jet induces a well-organized cyclonic eddy angular momentum flux, which acts as a momentum forcing that enhances the upper-level outflow and low-level inflow and favors the growth of the new TC.

scholarly journals Effects of close cutting on ground cover and quality of a polystand of Manilagrass and cool season turfgrasses

2019 ◽  
Vol 14 (1) ◽  
pp. 59-65
Author(s):  
Nicola Grossi ◽  
Marco Fontanelli ◽  
Christian Frasconi ◽  
Luisa Martelloni ◽  
Michele Raffaelli ◽  
...  
Keyword(s):  
Warm Season ◽  
Ground Cover ◽  
Shoot Density ◽  
The Other ◽  
Festuca Rubra ◽  
Cool Season ◽  
Low Input ◽  
Zoysia Matrella ◽  
Turf Quality

Warm season turfgrasses can be grown successfully in the transition zone, but dormancy occurs to some extent during the winter. Overseeding with cool-season turfgrasses is necessary if winter dormancy of warm season turfgrasses is not tolerated. The increasing availability of zoysiagrass cultivars has enabled this genus to be considered suitable for low-maintenance golf courses, especially for golf tees and golf fairways. On the other hand, zoysiagrasses have the most rigid leaves of all turfgrass species, followed by bermudagrasses and by the other warm season turf species. Thus, to have a high mowing quality, mowers working constantly on zoysiagrasses require more sharpening than mowers working on other grasses. Rotary mowers are not suitable for mowing at low heights and often result in scalping, while reel mowers perform optimal mowing at a short height (below 2.5 cm) but require accurate management and frequent sharpening. Autonomous mowers have proven to produce a superior turf quality compared with traditional walk-behind rotary mowers, but no autonomous mower has ever been tested at a low mowing height on an overseeded warm season turfgrass. Because of this, the trial was carried out to simulate a golf tee overseeded with cool season turfgrasses, with low input fertilisation rates and with one of the most difficult turf species to mow; i.e. Zoysia matrella (L.) Merr. The trial was carried out in San Piero a Grado (Pisa, Italy) from October 2016 to October 2018. After a two-year period the best turf quality was achieved with Festuca rubra L. ssp. cultivars among the overseeded species, especially during fall. In many cases turf quality increased after manila grass green up since the combination of both cool season and warm season species gave a higher quality to the turfgrass, due to the finer leaf texture and higher shoot density of some cool season species. Moreover, recovery of manila grass ground cover was satisficing. In conclusion, a polystand of manila grass and Festuca rubra ssp. could be suitable for golf tees with low-input management.

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