scholarly journals A Simple Analytical Model of the Nocturnal Low-Level Jet over the Great Plains of the United States

2014 ◽  
Vol 71 (10) ◽  
pp. 3674-3683 ◽  
Author(s):  
Yu Du ◽  
Richard Rotunno
Keyword(s):  
Friction Coefficient ◽  
Analytical Model ◽  
Great Plains ◽  
Present Model ◽  
The United States ◽  
Simple Analytical Model ◽  
Thermal Forcing ◽  
Low Level ◽  
Low Level Jet ◽  
Sloping Terrain

Abstract A simple analytical model including both diurnal thermal forcing over sloping terrain (the “Holton” mechanism) and diurnally varying boundary layer friction (the “Blackadar” mechanism) is developed to account for the observed amplitude and phase of the low-level jet (LLJ) over the Great Plains and to understand better the role of each mechanism. The present model indicates that, for the pure Holton mechanism (time-independent friction coefficient), the maximum southerly wind speed occurs (depending on the assumed friction coefficient) between sunset and midnight local standard time, which is earlier than the observed after-midnight maximum. For the pure Blackadar mechanism (time-independent thermal forcing), the present model shows that generally occurs later (closer to sunrise) than observed and has a strong latitudinal dependence. For both mechanisms combined, the present model indicates that occurs near to the observed time, which lies between the time obtained in the pure Holton mechanism and the time obtained in the pure Blackadar mechanism; furthermore, is larger (and closer to that observed) than in each one considered individually. The amplitude and phase of the LLJ as a function of latitude can be obtained by the combined model by allowing for the observed latitude-dependent mean and diurnally varying thermal forcing.

scholarly journals Climatic factors contributing to long-term variations of fine dust concentration in the United States

2017 ◽  
Author(s):  
Bing Pu ◽  
Paul Ginoux
Keyword(s):  
Great Plains ◽  
The United States ◽  
Dust Concentration ◽  
Dust Particles ◽  
Positive Trend ◽  
Fine Dust ◽  
Low Level ◽  
Low Level Jet ◽  
Long Term Variations

Abstract. High concentration of dust particles can cause respiratory problems and increase non-accidental mortality. Studies found fine dust (with aerodynamic diameter less than 2.5 microns) is an important component of the total PM2.5 mass in the western and central U.S. in spring and summer and has positive trends. This work examines factors influencing long-term variations of fine dust concentration in the U.S. using station data from the Interagency Monitoring Protected Visual Environments (IMPROVE) network during 1990–2015. The variations of the fine dust concentration can be largely explained by the variations of precipitation, surface bareness, and 10 m wind speed. Moreover, including convective parameters such as convective inhibition (CIN) and convective available potential energy (CAPE) better explains the variations and trends over the Great Plains from spring to fall. While the positive trend of fine dust concentration in the Southwest in spring is associated with precipitation deficit, the increasing of fine dust over the central Great Plains in summer is largely associated with an enhancing of CIN and a weakening of CAPE, which are related to increased atmospheric stability due to surface drying and lower troposphere warming. The positive trend of the Great Plains low-level jet also contributes to the increasing of fine dust concentration in the central Great Plains in summer via its connections with surface winds and CIN. Summer dusty days in the central Great Plains are usually associated with a westward extension of the North Atlantic subtropical high that intensifies the Great Plains low-level jet and also results in a stable atmosphere with subsidence and reduced precipitation.

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>

scholarly journals Atmospheric Moisture Transport over the United States and Mexico as Evaluated in the NCEP Regional Reanalysis

2005 ◽  
Vol 6 (5) ◽  
pp. 710-728 ◽  
Author(s):  
Kingtse C. Mo ◽  
Muthuvel Chelliah ◽  
Marco L. Carrera ◽  
R. Wayne Higgins ◽  
Wesley Ebisuzaki
Keyword(s):  
United States ◽  
Gulf Of Mexico ◽  
Great Plains ◽  
Moisture Transport ◽  
Gulf Of California ◽  
Phase Relationship ◽  
The United States ◽  
Low Level ◽  
Low Level Jet ◽  
Regional Reanalysis

Abstract The large-scale atmospheric hydrologic cycle over the United States and Mexico derived from the 23-yr NCEP regional reanalysis (RR) was evaluated by comparing the RR products with satellite estimates, independent sounding data, and the operational Eta Model three-dimensional variational data assimilation (3DVAR) system (EDAS). In general, the winter atmospheric transport and precipitation are realistic. The climatology and interannual variability of the Pacific, subtropical jet streams, and low-tropospheric moisture transport are well captured. During the summer season, the basic features and the evolution of the North American monsoon (NAM) revealed by the RR compare favorably with observations. The RR also captures the out-of-phase relationship of precipitation as well as the moisture flux convergence between the central United States and the Southwest. The RR is able to capture the zonal easterly Caribbean low-level jet (CALLJ) and the meridional southerly Great Plains low-level jet (GPLLJ). Together, they transport copious moisture from the Caribbean to the Gulf of Mexico and from the Gulf of Mexico to the Great Plains, respectively. The RR systematically overestimates the meridional southerly Gulf of California low-level jet (GCLLJ). A comparison with observations suggests that the meridional winds from the RR are too strong, with the largest differences centered over the northern Gulf of California. The strongest winds over the Gulf in the RR extend above 700 hPa, while the operational EDAS and station soundings indicate that the GCLLJ is confined to the boundary layer.

scholarly journals Mesoscale Moisture Transport by the Low-Level Jet during the IHOP Field Experiment

2008 ◽  
Vol 136 (10) ◽  
pp. 3781-3795 ◽  
Author(s):  
Edward I. Tollerud ◽  
Fernando Caracena ◽  
Steven E. Koch ◽  
Brian D. Jamison ◽  
R. Michael Hardesty ◽  
...  
Keyword(s):  
Great Plains ◽  
Cross Sections ◽  
Moisture Transport ◽  
Large Scale ◽  
Wrf Model ◽  
The United States ◽  
Small Scale ◽  
Low Level ◽  
Convective Scale ◽  
Low Level Jet

Previous studies of the low-level jet (LLJ) over the central Great Plains of the United States have been unable to determine the role that mesoscale and smaller circulations play in the transport of moisture. To address this issue, two aircraft missions during the International H2O Project (IHOP_2002) were designed to observe closely a well-developed LLJ over the Great Plains (primarily Oklahoma and Kansas) with multiple observation platforms. In addition to standard operational platforms (most important, radiosondes and profilers) to provide the large-scale setting, dropsondes released from the aircraft at 55-km intervals and a pair of onboard lidar instruments—High Resolution Doppler Lidar (HRDL) for wind and differential absorption lidar (DIAL) for moisture—observed the moisture transport in the LLJ at greater resolution. Using these observations, the authors describe the multiscalar structure of the LLJ and then focus attention on the bulk properties and effects of scales of motion by computing moisture fluxes through cross sections that bracket the LLJ. From these computations, the Reynolds averages within the cross sections can be computed. This allow an estimate to be made of the bulk effect of integrated estimates of the contribution of small-scale (mesoscale to convective scale) circulations to the overall transport. The performance of the Weather Research and Forecasting (WRF) Model in forecasting the intensity and evolution of the LLJ for this case is briefly examined.

Nocturnal Destabilization Associated with the Summertime Great Plains Low-Level Jet

2020 ◽  
Vol 148 (11) ◽  
pp. 4641-4656
Author(s):  
Thomas R. Parish ◽  
Richard D. Clark ◽  
Todd D. Sikora
Keyword(s):  
Great Plains ◽  
The United States ◽  
Temperature Gradients ◽  
Gradient Force ◽  
Wind Component ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Low Level ◽  
Temperature Advection ◽  
Low Level Jet

AbstractThe Great Plains low-level jet (LLJ) has long been associated with summertime nocturnal convection over the central Great Plains of the United States. Destabilization effects of the LLJ are examined using composite fields assembled from the North American Mesoscale Forecast System for June and July 2008–12. Of critical importance are the large isobaric temperature gradients that become established throughout the lowest 3 km of the atmosphere in response to the seasonal heating of the sloping Great Plains. Such temperature gradients provide thermal wind forcing throughout the lower atmosphere, resulting in the establishment of a background horizontal pressure gradient force at the level of the LLJ. The attendant background geostrophic wind is an essential ingredient for the development of a pronounced summertime LLJ. Inertial turning of the ageostrophic wind associated with LLJ provides a westerly wind component directed normal to the terrain-induced orientation of the isotherms. Hence, significant nocturnal low-level warm-air advection occurs, which promotes differential temperature advection within a vertical column of atmosphere between the level just above the LLJ and 500 hPa. Such differential temperature advection destabilizes the nighttime troposphere above the radiatively cooled near-surface layer on a recurring basis during warm weather months over much of the Great Plains and adjacent states to the east. This destabilization process reduces the convective inhibition of air parcels near the level of the LLJ and may be of significance in the development of elevated nocturnal convection. The 5 July 2015 case from the Plains Elevated Convection at Night field program is used to demonstrate this destabilization process.

On the Role of Sloping Terrain in the Forcing of the Great Plains Low-Level Jet

2010 ◽  
Vol 67 (8) ◽  
pp. 2690-2699 ◽  
Author(s):  
Thomas R. Parish ◽  
Larry D. Oolman
Keyword(s):  
Great Plains ◽  
Mesoscale Model ◽  
Horizontal Resolution ◽  
Inertial Oscillation ◽  
Western Boundary ◽  
Boundary Current ◽  
Wind Maximum ◽  
Low Level ◽  
Low Level Jet ◽  
Sloping Terrain

Abstract The summertime Great Plains low-level jet (LLJ) has been the subject of numerous investigations during the past several decades. Characteristics of the LLJ include nighttime development of a pronounced wind maximum of typically 15–20 m s−1 at levels 300–800 m above the surface and a clockwise rotation of the wind maximum during the course of the night. Maximum frequency of occurrence of the LLJ is found in the southern Great Plains. Theories proposed to explain the diurnal wind maximum of the Great Plains LLJ include inertial oscillation of the ageostrophic wind, the diurnal oscillation of the horizontal pressure field associated with heating and cooling of the sloping terrain, and the western boundary current interpretations. A simple equation system and output from the 12-km horizontal resolution Weather Research and Forecasting Nonhydrostatic Mesoscale Model (NAM) for July 2008 are used to provide evidence as to the importance of the Great Plains topography in driving the LLJ. Summertime heating of the sloping terrain is critical in establishing the climatological position for the Great Plains LLJ. Heating enhances the background geostrophic flow associated with the Bermuda high, resulting in a maximum low-level mean summertime flow over the Great Plains region. Maximum geostrophic winds in the NAM are found during late afternoon, providing a large background wind on which frictional decoupling can act. The nighttime LLJ maximum is the result of an inertial oscillation of the unbalanced components that arise fundamentally from frictional decoupling. Diurnal heating of the sloping terrain forces a cycle in the geostrophic wind that is out of phase with the wind maximum.

scholarly journals The Seasonality of the Great Plains Low-Level Jet and ENSO Relationship

2015 ◽  
Vol 28 (11) ◽  
pp. 4525-4544 ◽  
Author(s):  
Lakshmi Krishnamurthy ◽  
Gabriel A. Vecchi ◽  
Rym Msadek ◽  
Andrew Wittenberg ◽  
Thomas L. Delworth ◽  
...  
Keyword(s):  
Great Plains ◽  
El Niño ◽  
Seasonal Changes ◽  
Climate Model ◽  
El Nino ◽  
Southern Oscillation ◽  
The United States ◽  
Boreal Summer ◽  
Low Level ◽  
Low Level Jet

Abstract This study investigates the seasonality of the relationship between the Great Plains low-level jet (GPLLJ) and the Pacific Ocean from spring to summer, using observational analysis and coupled model experiments. The observed GPLLJ and El Niño–Southern Oscillation (ENSO) relation undergoes seasonal changes with a stronger GPLLJ associated with La Niña in boreal spring and El Niño in boreal summer. The ability of the GFDL Forecast-Oriented Low Ocean Resolution (FLOR) global coupled climate model, which has the high-resolution atmospheric and land components, to simulate the observed seasonality in the GPLLJ–ENSO relationship is assessed. The importance of simulating the magnitude and phase locking of ENSO accurately in order to better simulate its seasonal teleconnections with the Intra-Americas Sea (IAS) is demonstrated. This study explores the mechanisms for seasonal changes in the GPLLJ–ENSO relation in model and observations. It is hypothesized that ENSO affects the GPLLJ variability through the Caribbean low-level jet (CLLJ) during the summer and spring seasons. These results suggest that climate models with improved ENSO variability would advance our ability to simulate and predict seasonal variations of the GPLLJ and their associated impacts on the United States.

scholarly journals Climatic factors contributing to long-term variations in surface fine dust concentration in the United States

2018 ◽  
Vol 18 (6) ◽  
pp. 4201-4215 ◽  
Author(s):  
Bing Pu ◽  
Paul Ginoux
Keyword(s):  
Great Plains ◽  
Climatic Factors ◽  
The United States ◽  
Dust Concentration ◽  
Dust Particles ◽  
Fine Dust ◽  
Low Level ◽  
Low Level Jet ◽  
Long Term Variations

Abstract. High concentrations of dust particles can cause respiratory problems and increase non-accidental mortality. Studies found fine dust (with an aerodynamic diameter of less than 2.5 µm) is an important component of the total PM2.5 mass in the western and central US in spring and summer and has positive trends. This work examines climatic factors influencing long-term variations in surface fine dust concentration in the US using station data from the Interagency Monitoring Protected Visual Environments (IMPROVE) network during 1990–2015. The variations in the fine dust concentration can be largely explained by the variations in precipitation, surface bareness, and 10 m wind speed. Moreover, including convective parameters such as convective inhibition (CIN) and convective available potential energy (CAPE) that reveal the stability of the atmosphere better explains the variations and trends over the Great Plains from spring to fall. While the positive trend of fine dust concentration in the southwestern US in spring is associated with precipitation deficit, the increase in fine dust over the central Great Plains in summer is largely associated with enhanced CIN and weakened CAPE, which are caused by increased atmospheric stability due to surface drying and lower-troposphere warming. The strengthening of the Great Plains low-level jet also contributes to the increase in fine dust concentration in the central Great Plains in summer via its positive correlation with surface winds and negative correlation with CIN. Summer dusty days in the central Great Plains are usually associated with a westward extension of the North Atlantic subtropical high that intensifies the Great Plains low-level jet and also results in a stable atmosphere with subsidence and reduced precipitation.

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