A Conceptual View on Inertial Oscillations and Nocturnal Low-Level Jets

2010 ◽  
Vol 67 (8) ◽  
pp. 2679-2689 ◽  
Author(s):  
B. J. H. Van de Wiel ◽  
A. F. Moene ◽  
G. J. Steeneveld ◽  
P. Baas ◽  
F. C. Bosveld ◽  
...  
Keyword(s):  
Inversion Layer ◽  
Geostrophic Wind ◽  
Wind Vector ◽  
Inertial Oscillations ◽  
Wind Speed Profile ◽  
Low Level ◽  
Low Level Jets ◽  
Low Level Jet ◽  
Nocturnal Inversion ◽  
Wind Profiles

Abstract In the present work Blackadar’s concept of nocturnal inertial oscillations is extended. Blackadar’s concept describes frictionless inertial oscillations above the nocturnal inversion layer. The current work includes frictional effects within the nocturnal boundary layer. It is shown that the nocturnal wind speed profile describes an oscillation around the nocturnal equilibrium wind vector, rather than around the geostrophic wind vector (as in the Blackadar case). By using this perspective, continuous time-dependent wind profiles are predicted. As such, information on both the height and the magnitude of the nocturnal low-level jet is available as a function of time. Preliminary analysis shows that the proposed extension performs well in comparison with observations when a simple Ekman model is used to represent the equilibrium state in combination with a realistic initial velocity profile. In addition to jet dynamics, backward inertial oscillations are predicted at lower levels close to the surface, which also appear to be present in observations. The backward oscillation forms an important mechanism behind weakening low-level winds during the afternoon transition. Both observational and theoretical modeling studies are needed to explore this phenomenon further.

scholarly journals Taklimakan Desert nocturnal low-level jet: climatology and dust activity

2016 ◽  
Vol 16 (12) ◽  
pp. 7773-7783 ◽  
Author(s):  
Jin Ming Ge ◽  
Huayue Liu ◽  
Jianping Huang ◽  
Qiang Fu
Keyword(s):  
Inversion Layer ◽  
Warm Season ◽  
Cold Season ◽  
Lower Atmosphere ◽  
Radiosonde Data ◽  
Taklimakan Desert ◽  
Convective Boundary ◽  
Low Level ◽  
Low Level Jets ◽  
Nocturnal Inversion

Abstract. While nocturnal low-level jets (NLLJs) occur frequently in many parts of the world, the occurrence and other detailed characteristics of NLLJs over the Taklimakan Desert (TD) are not well known. This paper presents a climatology of NLLJs and coincident dust over the TD by analyzing multi-year ERA-Interim reanalysis and satellite observations. It is found that the ERA-Interim dataset can capture the NLLJs' features well by comparison with radiosonde data from two surface sites. The NLLJs occur in more than 60 % of nights, which are primarily easterly to east-northeasterly. They typically appear at 100 to 400 m above the surface with a speed of 4 to 10 m s−1. Most NLLJs are located above the nocturnal inversion during the warm season, while they are embedded in the inversion layer during the cold season. NLLJs above the inversion have a strong annual cycle with a maximum frequency in August. We also quantify the convective boundary layer (CBL) height and construct an index to measure the magnitude of the momentum in the CBL. We find that the magnitude of momentum in the lower atmosphere from the top of the surface layer to the top of mixed layer is larger for NLLJ cases than for non-NLLJ cases, and in the warm season the downward momentum transfer process is more intense and rapid. The winds below the NLLJ core to the desert surface gain strength in summer and autumn, and these summer and autumn winds are coincident with an enhancement of aerosol optical depth. This indicates that the NLLJ is an important mechanism for dust activity and transport during the warm season over the Taklimakan.

On the Formation of an Elevated Nocturnal Inversion Layer in the Presence of a Low-Level Jet: A Case Study

2012 ◽  
Vol 144 (3) ◽  
pp. 441-449 ◽  
Author(s):  
Jakob Kutsher ◽  
Nitsa Haikin ◽  
Avi Sharon ◽  
Eyal Heifetz
Keyword(s):  
Inversion Layer ◽  
Low Level ◽  
Low Level Jet ◽  
Nocturnal Inversion

scholarly journals A 1D Theoretical Analysis of Northerly Low-Level Jets over the Great Plains

2017 ◽  
Vol 74 (10) ◽  
pp. 3419-3431 ◽  
Author(s):  
Joshua G. Gebauer ◽  
Evgeni Fedorovich ◽  
Alan Shapiro
Keyword(s):  
Great Plains ◽  
Equations Of Motion ◽  
Geostrophic Wind ◽  
Inertial Oscillation ◽  
Diurnal Changes ◽  
Convective Boundary ◽  
Low Level ◽  
Low Level Jets ◽  
Low Level Jet ◽  
Negative Buoyancy

Abstract The forcing of northerly low-level jets over the eastward-sloped terrain of the U.S. Great Plains was studied using a one-dimensional (1D) nonstationary analytical model based on the Boussinesq-approximated equations of motion and thermal energy. For northerly low-level jets, the forcing from diurnal changes in surface heating of the sloped terrain (Holton mechanism) is out of phase with the nocturnal inertial oscillation resulting from the cessation of turbulent mixing at sunset (Blackadar mechanism), which results in weaker northerly nocturnal low-level jets when compared to southerly nocturnal low-levels jets with the same-magnitude background pressure gradient forcing. Because of the Blackadar and Holton mechanisms acting out of phase, nocturnal northerly low-level jets cannot solely explain the northerly low-level jet maximum over the Great Plains found in climatological studies. It is shown that negative buoyancy values over the eastward-sloped terrain enhance the low-level northerly geostrophic wind, which can cause low-level jetlike wind profiles that do not necessarily depend on the diurnal cycle. However, nocturnal northerly low-level jets primarily caused by an inertial oscillation still occur when daytime mixing is strong and buoyancy is small at sunset. These conditions are possible when strong capping inversions are present in the daytime convective boundary layer. The occurrence of both types of northerly low-level jets, those caused by negative buoyancy values over the sloped terrain and those driven by an inertial oscillation, better explains the findings of previous low-level jet climatologies.

scholarly journals Taklimakan Desert Nocturnal Low Level Jet: Climatology and Dust Emission

2016 ◽  
Author(s):  
J. M. Ge ◽  
H. Y. Liu ◽  
J. P. Huang ◽  
Q. Fu
Keyword(s):  
Inversion Layer ◽  
Dust Emission ◽  
Warm Season ◽  
Cold Season ◽  
Radiosonde Data ◽  
Taklimakan Desert ◽  
Convective Boundary ◽  
Low Level ◽  
Low Level Jets ◽  
Nocturnal Inversion

Abstract. While nocturnal Low-Level Jets (NLLJs) occur frequently in many parts of the world, the occurrence and other detailed characteristics of NLLJs over the Taklimakan Desert (TD) are not well known. This paper presents a climatology of NLLJs and coincident dust over the TD by analyzing multi-year ERA-Interim reanalysis and satellite observations. It is found that the ERA-Interim dataset can capture the NLLJs feature well by comparing with radiosonde data from two surface sites. The NLLJs occur in more than 60 % of nights, which are primarily easterly to east-northeasterly. They typically appear at 100 to 400 m above the surface with a speed of 4 to 10 ms−1. Most NLLJs are located above the nocturnal inversion during warm season while they are embedded in the inversion layer during cold season. NLLJs above the inversion have a strong annual cycle with a maximum frequency in August. We also quantify the convective boundary layer (CBL) height and construct an index to measure the magnitude of the momentum in the CBL. We find that the NLLJ contains more momentum than without NLLJ, and in warm season the downward momentum transfer process is more intense and rapid. The winds below the NLLJ core to the desert surface gain strength in summer and autumn, which are coincident with an enhancement of aerosol optical depth. It indicates that the NLLJ is an important mechanism for dust emission and transport during the warm season over the Taklimakan.

scholarly journals A Climatology of Nocturnal Low-Level Jets at Cabauw

2009 ◽  
Vol 48 (8) ◽  
pp. 1627-1642 ◽  
Author(s):  
P. Baas ◽  
F. C. Bosveld ◽  
H. Klein Baltink ◽  
A. A. M. Holtslag
Keyword(s):  
Wind Speed ◽  
Ground Level ◽  
Geostrophic Wind ◽  
Stable Stratification ◽  
Radiative Cooling ◽  
Inertial Oscillation ◽  
Stable Boundary Layers ◽  
Above Ground Level ◽  
Low Level ◽  
Low Level Jets

Abstract A climatology of nocturnal low-level jets (LLJs) is presented for the topographically flat measurement site at Cabauw, the Netherlands. LLJ characteristics are derived from a 7-yr half-hourly database of wind speed profiles, obtained from the 200-m mast and a wind profiler. Many LLJs at Cabauw originate from an inertial oscillation, which develops after sunset in a layer decoupled from the surface by stable stratification. The data are classified to different types of stable boundary layers by using the geostrophic wind speed and the isothermal net radiative cooling as classification parameters. For each of these classes, LLJ characteristics like frequency of occurrence, height above ground level, and the turning of the wind vector across the boundary layer are determined. It is found that LLJs occur in about 20% of the nights, are typically situated at 140–260 m above ground level, and have a speed of 6–10 m s−1. Development of a substantial LLJ is most likely to occur for moderate geostrophic forcing and a high radiative cooling. A comparison with the 40-yr ECMWF Re-Analysis (ERA-40) is added to illustrate how the results can be used to evaluate the performance of atmospheric models.

scholarly journals The Moisture Sources and Transport Processes for a Sudden Rainstorm Associated with Double Low-Level Jets in the Northeast Sichuan Basin of China

Atmosphere ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 160 ◽  
Author(s):  
Fangli Zhang ◽  
Guoping Li ◽  
Jun Yue
Keyword(s):  
South China Sea ◽  
South China ◽  
Moisture Transport ◽  
Sichuan Basin ◽  
Arabian Sea ◽  
Low Level ◽  
China Sea ◽  
Northeast Sichuan Basin ◽  
Low Level Jets ◽  
Low Level Jet

A sudden rainstorm that occurred in the northeast Sichuan Basin of China in early May 2017 was associated with a southwest low-level jet (SWLJ) and a mountainous low-level jet (MLLJ). This study investigates the impact of the double low-level jets (LLJs) on rainfall diurnal variation by using the data from ERA5 reanalysis, and explores the characteristics of water vapor transport, including the main paths and sources of moisture, by using the HYSPLIT-driven data of the ERA—interim, GDAS (Global Data Assimilation System), and NCEP/NCAR reanalysis data. The analysis shows that the sudden rainstorm in the mountain terrain was located at the left side of the large-scale SWLJ at 700 hPa, and at the exit region of the meso-scale MLLJ at 850 hPa. The double LLJs provide favorable moisture conditions, and the enhancement (weakening) of the LLJs is ahead of the start (end) of the rainstorm. The capacity of the LLJ at 850 hPa with respect to moisture convergence is superior to that at 700 hPa, especially when the MLLJ and the southerly LLJ at 850 hPa appear at the same time. The HYSPLIT backward trajectory model based on Lagrangian methods has favorable applicability in the event of sudden rainstorms in mountainous terrain, and there is no special path of moisture transport in this precipitation event. The main moisture sources of this process are the East China Sea–South China Sea, the Arabian Sea–Indian Peninsula, the Bay of Bengal, and the Middle East, accounting for 38%, 34%, 17% and 11% of the total moisture transport, respectively. Among them, the moisture transport in the Bay of Bengal and the South China Sea–East China Sea is mainly located in the lower troposphere, which is below 900 hPa, while the moisture transport in the Arabian Sea–Indian Peninsula and the Middle East is mainly in the middle and upper layers of the troposphere. The moisture changes of the transport trajectories are affected by the topography, especially the high mountains around the Sichuan Basin.

scholarly journals Low-Level Jets in the North American Regional Reanalysis (NARR): A Comparison with Rawinsonde Observations

2014 ◽  
Vol 53 (9) ◽  
pp. 2093-2113 ◽  
Author(s):  
Claudia K. Walters ◽  
Julie A. Winkler ◽  
Sara Husseini ◽  
Ryan Keeling ◽  
Jovanka Nikolic ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
North American ◽  
Low Level ◽  
The North ◽  
Central United States ◽  
North American Regional Reanalysis ◽  
Low Level Jets ◽  
Regional Reanalysis ◽  
Wind Profiles ◽  
Fine Resolution

AbstractClimatological analyses of low-level jets (LLJs) can be negatively influenced by the coarse spatial and temporal resolution and frequent changes in observing and archiving protocols of rawinsonde observations (raobs). The introduction of reanalysis datasets, such as the North American Regional Reanalysis (NARR), provides new resources for climatological research with finer spatial and temporal resolution and potentially fewer inhomogeneities. To assess the compatibility of LLJ characteristics identified from NARR wind profiles with those obtained from raob profiles, LLJs were extracted using standard jet definitions from NARR and raobs at 12 locations in the central United States for four representative years that reflect different rawinsonde protocols. LLJ characteristics (e.g., between-station differences in relative frequency, diurnal fluctuations, and mean speed and elevation) are generally consistent, although absolute frequencies are smaller for NARR relative to raobs at most stations. LLJs are concurrently identified in the NARR and raob wind profiles on less than 60% of the observation times with LLJ activity. Variations are seen between analysis years and locations. Of particular note is the substantial increase in LLJ frequency seen in raobs since the introduction of the Radiosonde Replacement System, which has led to a greater discrepancy in jet frequency between the NARR and raob datasets. The analyses suggest that NARR is a viable additional resource for climatological analyses of LLJs. Many of the findings are likely applicable for other fine-resolution reanalysis datasets, although differences between reanalyses require that each be carefully evaluated before its use in climatological analyses of wind maxima.

scholarly journals Pristine Nocturnal Convective Initiation: A Climatology and Preliminary Examination of Predictability

2017 ◽  
Vol 32 (4) ◽  
pp. 1613-1635 ◽  
Author(s):  
Sean Stelten ◽  
William A. Gallus
Keyword(s):  
Great Plains ◽  
Wrf Model ◽  
Geostrophic Wind ◽  
Formation Mechanisms ◽  
Convective Initiation ◽  
Lower Altitude ◽  
Low Level ◽  
Preliminary Examination ◽  
Low Level Jet ◽  
The Times

Abstract The prediction of convective initiation remains a challenge to forecasters in the Great Plains, especially for elevated events at night. This study examines a subset of 287 likely elevated nocturnal convective initiation events that occurred with little or no direct influence from surface boundaries or preexisting convection over a 4-month period of May–August during the summer of 2015. Events were first classified into one of four types based on apparent formation mechanisms and location relative to any low-level jet. A climatology of each of the four types was performed focusing on general spatial tendencies over a large Great Plains domain and initiation timing trends. Simulations from five convection-allowing models available during the Plains Elevated Convection At Night (PECAN) field campaign, along with four versions of a 4-km Weather Research and Forecasting (WRF) Model, were used to examine the predictability of these types of convective initiation. A dual-peak pattern for initiation timing was revealed, with one peak near 0400 UTC and another around 0700 UTC. The times and prominence of each peak shifted depending on the region analyzed. Positive thermal advection by the geostrophic wind was present in the majority of events for three types but not for the type occurring without a low-level jet. Models were more deficient with location than timing for the five PECAN models, with the four 4-km WRF Models showing similar location errors and problems with initiating convection at a lower altitude than observed.

scholarly journals Summertime Low-Level Jets over the High-Latitude Arctic Ocean

2008 ◽  
Vol 47 (6) ◽  
pp. 1770-1784 ◽  
Author(s):  
Douglas O. ReVelle ◽  
E. Douglas Nilsson
Keyword(s):  
Boundary Layer ◽  
Eddy Viscosity ◽  
Low Level ◽  
Rayleigh Friction ◽  
Low Level Jets ◽  
Low Level Jet ◽  
Horizontal Momentum ◽  
Ocean Observations ◽  
Measured Wind Speed ◽  
Good Agreement

Abstract The application of a simple analytic boundary layer model developed by Thorpe and Guymer did not produce good agreement with observational data for oceanic low-level jet observations even though this model has worked well for the predictions of low-level jets over continental surfaces. This failure to properly predict the boundary layer wind maxima was very puzzling because more detailed numerical boundary layer models have properly predicted these low-level oceanic wind maxima. To understand the reasons for its failure to explain the ocean observations, the authors modified the frictional terms in the horizontal linear momentum equations of Thorpe and Guymer, using a standard eddy viscosity closure technique instead of the Rayleigh friction parameterization originally used. This improvement in the modeling of the dissipation terms, which has resulted in the use of an enhanced Rayleigh friction parameterization in the horizontal momentum equations, modified the boundary layer winds such that the continental predictions remained nearly identical to those predicted previously using the Thorpe and Guymer model while the oceanic predictions have now become more representative of the measured wind speed from recent Arctic expeditions.

scholarly journals A Unified Theory for the Great Plains Nocturnal Low-Level Jet

2016 ◽  
Vol 73 (8) ◽  
pp. 3037-3057 ◽  
Author(s):  
Alan Shapiro ◽  
Evgeni Fedorovich ◽  
Stefan Rahimi
Keyword(s):  
Great Plains ◽  
Slope Angle ◽  
Geostrophic Wind ◽  
Linear Functions ◽  
Free Atmosphere ◽  
Wind Maximum ◽  
Maximum Surface ◽  
Low Level ◽  
Low Level Jet ◽  
Surface Buoyancy

Abstract A theory is presented for the Great Plains low-level jet in which the jet emerges in the sloping atmospheric boundary layer as the nocturnal phase of an oscillation arising from diurnal variations in turbulent diffusivity (Blackadar mechanism) and surface buoyancy (Holton mechanism). The governing equations are the equations of motion, mass conservation, and thermal energy for a stably stratified fluid in the Boussinesq approximation. Attention is restricted to remote (far above slope) geostrophic winds that blow along the terrain isoheights (southerly for the Great Plains). Diurnally periodic solutions are obtained analytically with diffusivities that vary as piecewise constant functions of time and slope buoyancies that vary as piecewise linear functions of time. The solution is controlled by 11 parameters: slope angle, Coriolis parameter, free-atmosphere Brunt–Väisälä frequency, free-atmosphere geostrophic wind, radiative damping parameter, day and night diffusivities, maximum and minimum surface buoyancies, and times of maximum surface buoyancy and sunset. The Holton mechanism, by itself, results in relatively weak wind maxima but produces strong jets when paired with the Blackadar mechanism. Jets with both Blackadar and Holton mechanisms operating are shown to be broadly consistent with observations and climatological analyses. Jets strengthen with increasing geostrophic wind, maximum surface buoyancy, and day-to-night ratio of the diffusivities and weaken with increasing Brunt–Väisälä frequency and magnitude of minimum slope buoyancy (greater nighttime cooling). Peak winds are maximized for slope angles characteristic of the Great Plains.

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