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.

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.

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 Convection Initiation Caused by Heterogeneous Low-Level Jets over the Great Plains

2018 ◽  
Vol 146 (8) ◽  
pp. 2615-2637 ◽  
Author(s):  
Joshua G. Gebauer ◽  
Alan Shapiro ◽  
Evgeni Fedorovich ◽  
Petra Klein
Keyword(s):  
Great Plains ◽  
Three Dimensional ◽  
Warm Season ◽  
The United States ◽  
Dimensional Structure ◽  
Nonuniform Heating ◽  
Low Level ◽  
Low Level Jets ◽  
Convection Initiation ◽  
Capping Inversion

AbstractObservations from three nights of the Plains Elevated Convection at Night (PECAN) field campaign were used in conjunction with Rapid Refresh model forecasts to find the cause of north–south lines of convection, which initiated away from obvious surface boundaries. Such pristine convection initiation (CI) is relatively common during the warm season over the Great Plains of the United States. The observations and model forecasts revealed that all three nights had horizontally heterogeneous and veering-with-height low-level jets (LLJs) of nonuniform depth. The veering and heterogeneity were associated with convergence at the top-eastern edge of the LLJ, where moisture advection was also occurring. As time progressed, this upper region became saturated and, due to its placement above the capping inversion, formed moist absolutely unstable layers, from which the convergence helped initiate elevated convection. The structure of the LLJs on the CI nights was likely influenced by nonuniform heating across the sloped terrain, which led to the uneven LLJ depth and contributed toward the wind veering with height through the creation of horizontal buoyancy gradients. These three CI events highlight the importance of assessing the full three-dimensional structure of the LLJ when forecasting nocturnal convection over the Great Plains.

scholarly journals Speciated mercury at marine, coastal, and inland sites in New England – Part 1: Temporal variability

2012 ◽  
Vol 12 (11) ◽  
pp. 5099-5112 ◽  
Author(s):  
H. Mao ◽  
R. Talbot
Keyword(s):  
New England ◽  
Marine Boundary Layer ◽  
Limit Of Detection ◽  
Inversion Layer ◽  
Warm Season ◽  
Elemental Mercury ◽  
Positive Trend ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
Nocturnal Inversion

Abstract. A comprehensive analysis was conducted using long-term continuous measurements of gaseous elemental mercury (Hg0), reactive gaseous mercury (RGM), and particulate phase mercury (HgP) at coastal (Thompson Farm, denoted as TF), marine (Appledore Island, denoted as AI), and elevated inland (Pac Monadnock, denoted as PM) sites from the AIRMAP Observatories in southern New Hampshire, USA. Decreasing trends in background Hg0 were identified in the 7.5- and 5.5-yr records at TF and PM with decline rates of 3.3 parts per quadrillion by volume (ppqv) yr−1 and 6.3 ppqv yr−1, respectively. Common characteristics at these sites were the reproducible annual cycle of Hg0 with its maximum in winter-spring and minimum in fall, comprised of a positive trend in the warm season (spring – early fall) and a negative one in the cool season (late fall – winter). Year-to-year variability was observed in the warm season decline in Hg0 at TF varying from a minimum total (complete) seasonal loss of 43 ppqv in 2009 to a maximum of 92 ppqv in 2005, whereas variability remained small at AI and PM. The coastal site TF differed from the other two sites with its exceptionally low levels (as low as below 50 ppqv) in the nocturnal inversion layer possibly due to dissolution in dew water. Measurements of Hg0 at PM exhibited the smallest diurnal to annual variability among the three environments, where peak levels rarely exceeded 250 ppqv and the minimum was typically 100 ppqv. It should be noted that summertime diurnal patterns at TF and AI were opposite in phase indicating strong sink(s) for Hg0 during the day in the marine boundary layer, which was consistent with the hypothesis of Hg0 oxidation by halogen radicals there. Mixing ratios of RGM in the coastal and marine boundary layers reached annual maxima in spring and minima in fall, whereas at PM levels were generally below the limit of detection (LOD) except in spring. RGM levels at AI were higher than at TF and PM indicating a stronger source strength in the marine environment. Mixing ratios of HgP at AI and TF were close in magnitude to RGM levels and were mostly below 1 ppqv. Diurnal variation in HgP was barely discernible at TF and AI in spring and summer. Higher levels of HgP were observed during the day, while values that were smaller, but above the LOD, occurred at night.

scholarly journals Low-Level Jets over the Mid-Atlantic States: Warm-Season Climatology and a Case Study

2006 ◽  
Vol 45 (1) ◽  
pp. 194-209 ◽  
Author(s):  
Da-Lin Zhang ◽  
Shunli Zhang ◽  
Scott J. Weaver
Keyword(s):  
Real Time ◽  
Great Plains ◽  
Thermal Gradient ◽  
Warm Season ◽  
Heat Fluxes ◽  
Time Model ◽  
Low Level ◽  
Mountainous Regions ◽  
Low Level Jets

Abstract Although considerable research has been conducted to study the characteristics of the low-level jets (LLJs) over the Great Plains states, little is known about the development of LLJs over the Mid-Atlantic states. In this study, the Mid-Atlantic LLJ and its associated characteristics during the warm seasons of 2001 and 2002 are documented with both the wind profiler data and the daily real-time model forecast products. A case study with three model sensitivity simulations is performed to gain insight into the three-dimensional structures and evolution of an LLJ and the mechanisms by which it developed. It is found that the Mid-Atlantic LLJ, ranging from 8 to 23 m s−1, appeared at an average altitude of 670 m and on 15–25 days of each month. About 90% of the 160 observed LLJ events occurred between 0000 and 0600 LST, and about 60% had southerly to westerly directions. Statistically, the real-time forecasts capture most of the LLJ events with nearly the right timing, intensity, and altitude, although individual forecasts may not correspond to those observed. For a selected southwesterly LLJ case, both the observations and the control simulation exhibit a pronounced diurnal cycle of horizontal winds in the lowest 1.5 km. The simulation shows that the Appalachian Mountains tend to produce a sloping mixed layer with northeasterly thermal winds during the daytime and reversed thermal winds after midnight. With additional thermal contrast effects associated with the Chesapeake Bay and the Atlantic Ocean, the daytime low-level winds vary significantly from the east coast to the mountainous regions. The LLJ after midnight tends to be peaked preferentially around 77.5°W near the middle portion of the sloping terrain, and it decreases eastward as a result of the opposite thermal gradient across the coastline from the mountain-generated thermal gradient. Although the Mid-Atlantic LLJ is much weaker and less extensive than that over the Great Plains states, it has a width of 300–400 km (to its half-peak value) and a length scale of more than 1500 km, following closely the orientation of the Appalachians. Sensitivity simulations show that eliminating the surface heat fluxes produces the most significant impact on the development of the LLJ, then topography and the land–sea contrast, with its area-averaged intensity reduced from 12 m s−1 to about 6, 9, and 10 m s−1, respectively.

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

The diminishing contribution of low-level jets to the U.S. Great Plains water budget

2021 ◽  
Author(s):  
Craig R. Ferguson
Keyword(s):  
Water Vapor ◽  
Great Plains ◽  
Water Budget ◽  
Structural Changes ◽  
Warm Season ◽  
Water Vapor Transport ◽  
Northern Great Plains ◽  
Wind Maximum ◽  
Low Level ◽  
Low Level Jets

<p>In the semi-arid U.S. Great Plains, nocturnal southerly low-level jets (LLJs) serve critical roles as conveyors of remotely-sourced (i.e., Gulf of Mexico) water vapor and agents of atmospheric instability in the warm-season.  Defined by a diurnally oscillating wind maximum between 0–3 km above the surface, LLJs have been studied by meteorologists for over 60-years due to their role in severe weather outbreaks. It is only within the past decade that a subset of LLJs with especially high vertically integrated water vapor transport, termed atmospheric rivers, have drawn the attention of hydrologists.</p><p>In this study, changes in LLJ frequency and structure over the period from 1901–2010 are quantified using ECMWF’s Coupled Reanalysis of the Twentieth Century (CERA-20C). A new objective dynamical LLJ classification dataset is used to separately quantify changes in the two predominant LLJ types: synoptically coupled and uncoupled. The findings reveal that both the frequency of Great Plains LLJs and their associated precipitation have decreased significantly over the 20th century. Decreases in LLJ associated precipitation range between 10–14% of total present day May–September precipitation. The largest differences observed are attributable to uncoupled jet frequency and structural changes during July and August over the central and northern Great Plains. Overall, the results indicate the contribution of LLJs to the region’s water budget has diminished.</p>

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