scholarly journals Climatology of the Low-Level Jet at the Southern Great Plains Atmospheric Boundary Layer Experiments Site

2005 ◽  
Vol 44 (10) ◽  
pp. 1593-1606 ◽  
Author(s):  
Jie Song ◽  
Ke Liao ◽  
Richard L. Coulter ◽  
Barry M. Lesht
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Great Plains ◽  
Large Scale ◽  
Ground Level ◽  
Northerly Wind ◽  
Low Level ◽  
The Pacific ◽  
Terrain Following ◽  
Low Level Jet

Abstract A unique dataset obtained with combinations of minisodars and 915-MHz wind profilers at the Atmospheric Boundary Layer Experiments (ABLE) facility in Kansas was used to examine the detailed characteristics of the nocturnal low-level jet (LLJ). In contrast to instruments used in earlier studies, the ABLE instruments provide hourly, high-resolution vertical profiles of wind velocity from just above the surface to approximately 2 km above ground level (AGL). Furthermore, the 6-yr span of the dataset allowed the examination of interannual variability in jet properties with improved statistical reliability. It was found that LLJs occurred during 63% of the nighttime periods sampled. Although most of the observed jets were southerly, a substantial fraction (28%) was northerly. Wind maxima occurred most frequently at 200–400 m AGL, though some jets were found as low as 50 m, and the strongest jets tended to occur above 300 m. Comparison of LLJ heights at three locations within the ABLE domain and at one location outside the domain suggests that the jet is equipotential rather than terrain following. The occurrence of southerly LLJ varied annually in a way that suggests a connection between the tendency for jet formation and the large-scale circulation patterns associated with El Niño and La Niña, as well as with the Pacific decadal oscillation. Frequent and strong southerly jets that transport moisture downstream do not necessarily lead to more precipitation locally, however.

scholarly journals Variability of the Great Plains Low-Level Jet: Large-Scale Circulation Context and Hydroclimate Impacts

2008 ◽  
Vol 21 (7) ◽  
pp. 1532-1551 ◽  
Author(s):  
Scott J. Weaver ◽  
Sumant Nigam
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Core Region ◽  
Large Scale Circulation ◽  
Diurnal Variability ◽  
Low Level ◽  
The Pacific ◽  
Gulf States ◽  
Low Level Jet ◽  
Peak Phase

Abstract Variability of the Great Plains low-level jet (GPLLJ) is analyzed from the perspective of larger-scale, lower-frequency influences and regional hydroclimate impacts as opposed to the usual analysis of its frequency, diurnal variability, and mesoscale structure. The circulation-centric core analysis is conducted with monthly data from the high spatiotemporal resolution, precipitation-assimilating North American Regional Reanalysis, and the 40-yr ECMWF Re-Analysis (ERA-40) (as necessary) to identify the recurrent patterns of GPLLJ variability and their large-scale circulation links. The links are first investigated from regressions of an index representing meridional wind speed in the climatological jet-core region; the core region itself is defined from analysis of seasonal and diurnal variability of the jet structure and moisture fluxes. The analysis reveals that GPLLJ variability is, indeed, linked to coherent, large-scale, upper-level height patterns over the Pacific and North Atlantic Oscillation (NAO) variability in the Atlantic. A Rossby wave source analysis shows the Pacific height pattern to be potentially linked to tropical diabatic heating anomalies in the west-central basin and in the eastern Pacific sector. EOF analysis of GPLLJ variability shows it to be composed of three modes that, together, account for ∼75% of the variance. The modes represent the strengthening/expansion of the jet core (38%), with a strong precipitation impact on the northern Great Plains, and linked to post-peak-phase ENSO variability; meridional shift of the GPLLJ (23%), with a Gulf states precipitation focus, and linked to pre-peak-phase ENSO variability; and in-place strengthening of the GPLLJ (12%), with dipolar influence on Great Plains and Gulf states precipitation, and linked to summer NAO variability.

scholarly journals Impacts of Modifications to a Local Planetary Boundary Layer Scheme on Forecasts of the Great Plains Low-Level Jet Environment

2018 ◽  
Vol 33 (5) ◽  
pp. 1109-1120 ◽  
Author(s):  
David E. Jahn ◽  
William A. Gallus
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Planetary Boundary Layer ◽  
Great Plains ◽  
Potential Temperature ◽  
Specific Humidity ◽  
Low Level ◽  
Stable Conditions ◽  
Pbl Scheme ◽  
Low Level Jet

Abstract The Great Plains low-level jet (LLJ) is influential in the initiation and evolution of nocturnal convection through the northward advection of heat and moisture, as well as convergence in the region of the LLJ nose. However, accurate numerical model forecasts of LLJs remain a challenge, related to the performance of the planetary boundary layer (PBL) scheme in the stable boundary layer. Evaluated here using a series of LLJ cases from the Plains Elevated Convection at Night (PECAN) program are modifications to a commonly used local PBL scheme, Mellor–Yamada–Nakanishi–Niino (MYNN), available in the Weather Research and Forecasting (WRF) Model. WRF forecast mean absolute error (MAE) and bias are calculated relative to PECAN rawinsonde observations. The first MYNN modification invokes a new set of constants for the scheme closure equations that, in the vicinity of the LLJ, decreases forecast MAEs of wind speed, potential temperature, and specific humidity more than 19%. For comparison, the Yonsei University (YSU) scheme results in wind speed MAEs 22% lower but specific humidity MAEs 17% greater than in the original MYNN scheme. The second MYNN modification, which incorporates the effects of potential kinetic energy and uses a nonzero mixing length in stable conditions as dependent on bulk shear, reduces wind speed MAEs 66% for levels below the LLJ, but increases MAEs at higher levels. Finally, Rapid Refresh analyses, which are often used for forecast verification, are evaluated here and found to exhibit a relatively large average wind speed bias of 3 m s−1 in the region below the LLJ, but with relatively small potential temperature and specific humidity biases.

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 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.

Recurrent Supersynoptic Evolution of the Great Plains Low-Level Jet

2011 ◽  
Vol 24 (2) ◽  
pp. 575-582 ◽  
Author(s):  
Scott J. Weaver ◽  
Sumant Nigam
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Large Scale Circulation ◽  
Low Level ◽  
The North ◽  
Analysis Strategy ◽  
Precipitation Anomalies ◽  
North American Regional Reanalysis ◽  
Low Level Jet ◽  
Regional Reanalysis

Abstract The evolution of supersynoptic (i.e., pentad) Great Plains low-level jet (GPLLJ) variability, its precipitation impacts, and large-scale circulation context are analyzed in the North American Regional Reanalysis (NARR)—a high-resolution precipitation-assimilating dataset—and the NCEP–NCAR reanalysis. The analysis strategy leans on the extended EOF technique, which targets both spatial and temporal recurrence of a variability episode. Pentad GPLLJ variability structures are found to be spatially similar to those in the monthly analysis. The temporal evolution of the supersynoptic GPLLJ-induced precipitation anomalies reveal interesting lead and lag relationships highlighted by GPLLJ variability-leading precipitation anomalies. Interestingly, similar temporal phasing of the GPLLJ and precipitation anomalies were operative during the 1993 (1988) floods (drought) over the Great Plains, indicating the importance of these submonthly GPLLJ variability modes in the instigation of extreme hydroclimatic episodes. The northward-shifted (dry) GPLLJ variability mode is linked to large-scale circulation variations emanating from remote regions that are modified by interaction with the Rocky Mountains, suggesting that the supersynoptic GPLLJ fluctuations may have their origin in orographic modulation of baroclinic development.

scholarly journals WRF Model Study of the Great Plains Low-Level Jet: Effects of Grid Spacing and Boundary Layer Parameterization

2018 ◽  
Vol 57 (10) ◽  
pp. 2375-2397 ◽  
Author(s):  
Elizabeth N. Smith ◽  
Jeremy A. Gibbs ◽  
Evgeni Fedorovich ◽  
Petra M. Klein
Keyword(s):  
Boundary Layer ◽  
Great Plains ◽  
Wrf Model ◽  
High Temporal Resolution ◽  
Model Stability ◽  
Low Level ◽  
Model Study ◽  
Vertical Grid ◽  
Low Level Jet ◽  
Normal Scale

AbstractPrevious studies have shown that the Weather Research and Forecasting (WRF) Model often underpredicts the strength of the Great Plains nocturnal low-level jet (NLLJ), which has implications for weather, climate, aviation, air quality, and wind energy in the region. During the Lower Atmospheric Boundary Layer Experiment (LABLE) conducted in 2012, NLLJs were frequently observed at high temporal resolution, allowing for detailed documentation of their development and evolution throughout the night. Ten LABLE cases with observed NLLJs were chosen to systematically evaluate the WRF Model’s ability to reproduce the observed NLLJs. Model runs were performed with 4-, 2-, and 1-km horizontal spacing and with the default stretched vertical grid and a nonstretched 40-m vertically spaced grid to investigate which grid configurations are optimal for NLLJ modeling. These tests were conducted using three common boundary layer parameterization schemes: Mellor–Yamada Nakanishi Niino, Yonsei University, and Quasi-Normal Scale Elimination. It was found that refining horizontal spacing does not necessarily improve the modeled NLLJ wind. Increasing the number of vertical levels on a non-stretched grid provides more information about the structure of the NLLJ with some schemes, but the benefit is limited by computational expense and model stability. Simulations of the NLLJ were found to be less sensitive to boundary layer parameterization than to grid configuration. The Quasi-Normal Scale Elimination scheme was chosen for future NLLJ simulation studies.

scholarly journals An overview of the diurnal cycle of the atmospheric boundary layer during the West African monsoon season: results from the 2016 observational campaign

2018 ◽  
Vol 18 (4) ◽  
pp. 2913-2928 ◽  
Author(s):  
Norbert Kalthoff ◽  
Fabienne Lohou ◽  
Barbara Brooks ◽  
Gbenga Jegede ◽  
Bianca Adler ◽  
...  
Keyword(s):  
Boundary Layer ◽  
West Africa ◽  
Atmospheric Boundary Layer ◽  
Radiation Budget ◽  
Cloud Base ◽  
Data Set ◽  
Near Surface ◽  
Low Level ◽  
Synoptic Conditions ◽  
Low Level Jet

Abstract. A ground-based field campaign was conducted in southern West Africa from mid-June to the end of July 2016 within the framework of the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) project. It aimed to provide a high-quality comprehensive data set for process studies, in particular of interactions between low-level clouds (LLCs) and boundary-layer conditions. In this region missing observations are still a major issue. During the campaign, extensive remote sensing and in situ measurements were conducted at three supersites: Kumasi (Ghana), Savè (Benin) and Ile-Ife (Nigeria). Daily radiosoundings were performed at 06:00 UTC, and 15 intensive observation periods (IOPs) were performed during which additional radiosondes were launched, and remotely piloted aerial systems were operated. Extended stratiform LLCs form frequently in southern West Africa during the nighttime and persist long into the following day. They affect the radiation budget and hence the evolution of the atmospheric boundary layer and regional climate. The relevant parameters and processes governing the formation and dissolution of the LLCs are still not fully understood. This paper gives an overview of the diurnal cycles of the energy-balance components, near-surface temperature, humidity, wind speed and direction as well as of the conditions (LLCs, low-level jet) in the boundary layer at the supersites and relates them to synoptic-scale conditions (monsoon layer, harmattan layer, African easterly jet, tropospheric stratification) in the DACCIWA operational area. The characteristics of LLCs vary considerably from day to day, including a few almost cloud-free nights. During cloudy nights we found large differences in the LLCs' formation and dissolution times as well as in the cloud-base height. The differences exist at individual sites and also between the sites. The synoptic conditions are characterized by a monsoon layer with south-westerly winds, on average about 1.9 km deep, and easterly winds above; the depth and strength of the monsoon flow show great day-to-day variability. Within the monsoon layer, a nocturnal low-level jet forms in approximately the same layer as the LLC. Its strength and duration is highly variable from night to night. This unique data set will allow us to test some new hypotheses about the processes involved in the development of LLCs and their interaction with the boundary layer and can also be used for model evaluation.

scholarly journals Predictability of Midsummer Great Plains Low-Level Jet and Associated Precipitation

2020 ◽  
Vol 35 (1) ◽  
pp. 215-235 ◽  
Author(s):  
Kelsey M. Malloy ◽  
Ben P. Kirtman
Keyword(s):  
Great Plains ◽  
North American ◽  
Large Scale ◽  
Linear Regression Analysis ◽  
Intraseasonal Variability ◽  
Warm Season ◽  
Summer Precipitation ◽  
Climate System Model ◽  
Low Level ◽  
Low Level Jet

Abstract Warm-season precipitation in the U.S. “Corn Belt,” the Great Plains, and the Midwest greatly influences agricultural production and is subject to high interannual and intraseasonal variability. Unfortunately, current seasonal and subseasonal forecasts for summer precipitation have relatively low skill. Therefore, there are ongoing efforts to understand hydroclimate variability targeted at improving predictions, particularly through its primary transporter of moisture: the Great Plains low-level jet (LLJ). This study uses the Community Climate System Model, version 4 (CCSM4), July forecasts, made as part of the North American Multi-Model Ensemble (NMME), to assess skill in reproducing the monthly Great Plains LLJ and associated precipitation. Generally, the CCSM4 forecasts capture the climatological jet but have problems representing the observed variability beyond two weeks. In addition, there are predictors associated with the large-scale variability identified through linear regression analysis, shifts in kernel density estimators, and case study analysis that suggest potential for improving confidence in forecasts. In this study, a strengthened Caribbean LLJ, negative Pacific–North American (PNA) teleconnection, El Niño, and a negative Atlantic multidecadal oscillation each have a relatively strong and consistent relationship with a strengthened Great Plains LLJ. The circulation predictors, the Caribbean LLJ and PNA, present the greatest “forecast of opportunity” for considering and assigning confidence in monthly forecasts.

scholarly journals Long-lived high-frequency gravity waves in the atmospheric boundary layer: observations and simulations

2019 ◽  
Vol 19 (24) ◽  
pp. 15431-15446 ◽  
Author(s):  
Mingjiao Jia ◽  
Jinlong Yuan ◽  
Chong Wang ◽  
Haiyun Xia ◽  
Yunbin Wu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Gravity Waves ◽  
Horizontal Wind ◽  
Doppler Lidar ◽  
Low Level ◽  
Coherent Doppler Lidar ◽  
Computational Fluid Dynamics Cfd ◽  
Phase Progression ◽  
Low Level Jet

Abstract. A long-lived gravity wave (GW) in the atmospheric boundary layer (ABL) is analysed during a field experiment in Anqing, China (30∘37′ N, 116∘58′ E). Persistent GWs with periods ranging from 10 to 30 min over 10 h in the ABL within a 2 km height are detected by a coherent Doppler lidar from 4 to 5 September 2018. The amplitudes of the vertical wind due to these GWs are approximately 0.15–0.2 m s−1. The lifetimes of these GWs are longer than 20 wave cycles. There is no apparent phase progression with altitude. The vertical and zonal perturbations in the GWs are 90∘ out of phase, with vertical perturbations generally leading to zonal ones. Based on experiments and simplified two-dimensional computational fluid dynamics (CFD) numerical simulations, a reasonable generation mechanism of this persistent wave is proposed. A westerly low-level jet of ∼5 m s−1 exists at an altitude of 1–2 km in the ABL. The wind shear around the low-level jet leads to wave generation under the condition of light horizontal wind. Furthermore, a combination of thermal and Doppler ducts occurs in the ABL. Thus, the ducted wave motions are trapped in the ABL and have long lifetimes.

scholarly journals Observing and Simulating the Summertime Low-Level Jet in Central Iowa

2015 ◽  
Vol 143 (6) ◽  
pp. 2319-2336 ◽  
Author(s):  
Brian J. Vanderwende ◽  
Julie K. Lundquist ◽  
Michael E. Rhodes ◽  
Eugene S. Takle ◽  
Samantha L. Irvin
Keyword(s):  
Great Plains ◽  
Vertical Wind Shear ◽  
Ground Level ◽  
Turbine Rotor ◽  
Inertial Oscillation ◽  
Energy Forecasting ◽  
Site Assessment ◽  
Low Level ◽  
Low Level Jet ◽  
Wind Profiles

Abstract In the U.S. state of Iowa, the increase in wind power production has motivated interest into the impacts of low-level jets on turbine performance. In this study, two commercial lidar systems were used to sample wind profiles in August 2013. Jets were systematically detected and assigned an intensity rating from 0 (weak) to 3 (strong). Many similarities were found between observed jets and the well-studied Great Plains low-level jet in summer, including average jet heights between 300 and 500 m above ground level, a preference for southerly wind directions, and a nighttime bias for stronger jets. Strong vertical wind shear and veer were observed, as well as veering over time associated with the LLJs. Speed, shear, and veer increases extended into the turbine-rotor layer during intense jets. Ramp events, in which winds rapidly increase or decrease in the rotor layer, were also commonly observed during jet formation periods. The lidar data were also used to evaluate various configurations of the Weather Research and Forecasting Model. Jet occurrence exhibited a stronger dependence on the choice of initial and boundary condition data, while reproduction of the strongest jets was influenced more strongly by the choice of planetary boundary layer scheme. A decomposition of mean model winds suggested that the main forcing mechanism for observed jets was the inertial oscillation. These results have implications for wind energy forecasting and site assessment in the Midwest.

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