scholarly journals Interactions between a Nocturnal MCS and the Stable Boundary Layer as Observed by an Airborne Compact Raman Lidar during PECAN

2019 ◽  
Vol 147 (9) ◽  
pp. 3169-3189 ◽  
Author(s):  
Guo Lin ◽  
Bart Geerts ◽  
Zhien Wang ◽  
Coltin Grasmick ◽  
Xiaoqin Jing ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Layer Structure ◽  
Small Scale ◽  
Raman Lidar ◽  
Stable Boundary ◽  
Cold Pools ◽  
Outflow Boundary ◽  
The University ◽  
Frontal Boundary

Abstract Small-scale variations within the low-level outflow and inflow of an MCS can either support or deter the upscale growth and maintenance of the MCS. However, these small-scale variations, in particular in the thermodynamics (temperature and humidity), remain poorly understood, due to a lack of detailed measurements. The compact Raman lidar (CRL) deployed on the University of Wyoming King Air aircraft directly sampled temperature and water vapor profiles at unprecedented vertical and along-track resolutions along the southern margin of a series of mature nocturnal MCSs traveling along a frontal boundary on 1 July 2015 during the Plains Elevated Convection at Night (PECAN) campaign. Here, the capability of the airborne CRL to document interactions between the MCS inflow and outflow currents is illustrated. The CRL reveals the well-defined boundary of a cooler current. This is interpreted as the frontal boundary sharpened by convectively induced cold pools, in particular by the outflow boundary of the downstream MCS. In one CRL transect, the frontal/outflow boundary appeared as a distinct two-layer structure of moisture and aerosols formed by moist stable boundary layer air advected above the boundary. The second transect, one hour later, reveals a single sloping boundary. In both cases, the lofting of the moist stably stratified air over the boundary favors MCS maintenance, through enhanced elevated CAPE and reduced CIN. The CRL data are sufficiently resolved to reveal Kelvin–Helmholtz (KH) billows and the vertical structure of the outflow boundary, which in this case behaved as a density current rather than an undular bore.

scholarly journals The Relation between Nocturnal MCS Evolution and Its Outflow Boundaries in the Stable Boundary Layer: An Observational Study of the 15 July 2015 MCS in PECAN

2018 ◽  
Vol 146 (10) ◽  
pp. 3203-3226 ◽  
Author(s):  
Coltin Grasmick ◽  
Bart Geerts ◽  
David D. Turner ◽  
Zhien Wang ◽  
T. M. Weckwerth
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Cell Formation ◽  
Lower Troposphere ◽  
Radiosonde Data ◽  
Cold Pool ◽  
Density Currents ◽  
Raman Lidar ◽  
Stable Boundary ◽  
Outflow Boundary

Abstract The vertical structures of a leading outflow boundary ahead of a continental nocturnal MCS and of the upstream environment are examined in order to answer the question of whether this vertical structure affects new cell formation and thus MCS maintenance. The MCS in question, observed on 15 July 2015 as part of the Plains Elevated Convection at Night (PECAN) experiment, formed near sunset as a surface-based, density current–driven system. As the night progressed and a stable boundary layer developed, convection became elevated, multiple fine lines became apparent (indicative of an undular bore), and convection increasingly lagged the outflow boundary. Bore-like boundaries became most apparent where the outflow boundary was oriented more perpendicular to the low-level jet, and the lower troposphere was more susceptible to wave trapping. This case study uses a rich array of radiosonde data, as well as airborne Raman lidar and ground-based interferometer data, to profile the temperature and humidity in the lower troposphere. In all soundings, the lifting of air in the residual mixed layer over a depth corresponding to the Raman lidar observed vertical displacement reduced CIN to near zero and enabled deep convection, even though most unstable CAPE steadily decreased during the evolution of this MCS. Both types of outflow boundaries (density currents and bores) initiated convection that helped maintain the MCS. In the case of density currents, cold pool depth and wind shear determined new cell formation and thus MCS maintenance. For bore-like boundaries, bore transformation and propagation were additional factors that determined whether convection initiated and whether it contributed to the MCS or remained separated.

scholarly journals The meteorology and chemistry of high nitrogen oxide concentrations in the stable boundary layer at the South Pole

2018 ◽  
Vol 18 (5) ◽  
pp. 3755-3778 ◽  
Author(s):  
William Neff ◽  
Jim Crawford ◽  
Marty Buhr ◽  
John Nicovich ◽  
Gao Chen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Nitrogen Oxide ◽  
Stable Boundary Layer ◽  
Early Summer ◽  
Late Spring ◽  
Small Scale ◽  
South Pole ◽  
Stable Boundary ◽  
Direct Measurements ◽  
The Antarctic

Abstract. Four summer seasons of nitrogen oxide (NO) concentrations were obtained at the South Pole (SP) during the Sulfur Chemistry in the Antarctic Troposphere (ISCAT) program (1998 and 2000) and the Antarctic Tropospheric Chemistry Investigation (ANTCI) in (2003, 2005, 2006–2007). Together, analyses of the data collected from these studies provide insight into the large- to small-scale meteorology that sets the stage for extremes in NO and the significant variability that occurs day to day, within seasons, and year to year. In addition, these observations reveal the interplay between physical and chemical processes at work in the stable boundary layer of the high Antarctic plateau. We found a systematic evolution of the large-scale wind system over the ice sheet from winter to summer that controls the surface boundary layer and its effect on NO: initially in early spring (Days 280–310) the transport of warm air and clouds over West Antarctica dominates the environment over the SP; in late spring (Days 310–340), the winds at 300 hPa exhibit a bimodal behavior alternating between northwest and southeast quadrants, which is of significance to NO; in early summer (Days 340–375), the flow aloft is dominated by winds from the Weddell Sea; and finally, during late spring, winds aloft from the southeast are strongly associated with clear skies, shallow stable boundary layers, and light surface winds from the east – it is under these conditions that the highest NO occurs. Examination of the winds at 300 hPa from 1961 to 2013 shows that this seasonal pattern has not changed significantly, although the last twenty years have seen an increasing trend in easterly surface winds at the SP. What has also changed is the persistence of the ozone hole, often into early summer. With lower total ozone column density and higher sun elevation, the highest actinic flux responsible for the photolysis of snow nitrate now occurs in late spring under the shallow boundary layer conditions optimum for high accumulation of NO. This may occur via the non-linear HOX–NOx chemistry proposed after the first ISCAT field programs and NOx recycling to the surface where quantum yields may be large under the low-snow-accumulation regime of the Antarctic plateau. During the 2003 field program a sodar made direct measurements of the stable boundary layer depth (BLD), a key factor in explaining the chemistry of the high NO concentrations. Because direct measurements were not available in the other years, we developed an estimator for BLD using direct observations obtained in 2003 and step-wise linear regression with meteorological data from a 22 m tower (that was tested against independent data obtained in 1993). These data were then used with assumptions about the column abundance of NO to estimate surface fluxes of NOx. These results agreed in magnitude with results at Concordia Station and confirmed significant daily, intraseasonal and interannual variability in NO and its flux from the snow surface. Finally, we found that synoptic to mesoscale eddies governed the boundary layer circulation and accumulation pathways for NO at the SP rather than katabatic forcing. It was the small-scale features of the circulation including the transition from cloudy to clear conditions that set the stage for short-term extremes in NO, whereas larger-scale features were associated with more moderate concentrations.

scholarly journals The Meteorology and Chemistry of High Nitrogen Oxide Concentrations in the Stable Boundary Layer at the South Pole

2017 ◽  
Author(s):  
William Neff ◽  
Jim Crawford ◽  
Marty Buhr ◽  
John Nicovich ◽  
Gao Chen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Early Summer ◽  
Late Spring ◽  
Small Scale ◽  
South Pole ◽  
The South ◽  
Stable Boundary ◽  
Direct Measurements ◽  
The Antarctic

Abstract. Four summer seasons of nitrogen oxide (NO) concentrations were obtained at the South Pole during the Sulfur Chemistry in the Antarctic Troposphere (ISCAT) program (1998 and 2000) and the Antarctic Tropospheric Chemistry Investigation (ANTCI) in (2003, 2006–7). Together, analyses of their data here provide insight into the large-to-small scale meteorology that sets the stage for high NO and the significant variability that occurs day-to-day, within seasons and year-to-year. In addition, these observations reveal the interplay between physical and chemical processes at work in the stable boundary layer of the high Antarctic plateau. We found a systematic evolution of the large-scale wind system over the ice sheet from winter to summer that controls the surface boundary layer and its effect on NO: Initially in early spring (Days 280–310) the transport of warm air and clouds over West Antarctica dominates the environment over the South Pole; In late spring (Days 310–340), of significance to NO, the winds at 300-hPa exhibit a bimodal behavior alternating between NW and SE; In early summer (Days 340–375), the flow aloft is dominated by winds from the Weddell Sea. During late spring, winds aloft from the SE are strongly associated with clear skies, shallow stable boundary layers, and light surface winds from the east: it is under these conditions that the highest NO occurs. Examination of the winds at 300 hPa from 1961 to 2013 shows that this seasonal pattern has not changed significantly although the last twenty years have seen an increasing trend in easterly surface winds at the South Pole. What has also changed is the persistence of the ozone hole, often into early summer. With lower total ozone column density and higher sun elevation, the highest actinic flux responsible for the photolysis of snow nitrate now occurs in late spring under the shallow boundary layer conditions optimum for high accumulation of NO. This may occur via the non-linear HOX-NOX chemistry proposed after the first ISCAT field programs and NOX recycling to the surface where quantum yields may be large under the low-snow-accumulation regime of the Antarctic plateau. During the 2003 field program a sodar made direct measurements of the stable boundary layer depth (BLD), a key factor in explaining the chemistry of the high NO concentrations. Because direct measurements were not available in the other years, we developed an estimator for BLD using direct observations obtained in 2003 and step-wise linear regression with meteorological data from a 22-m tower (that was tested against independent data obtained in 1993). These data were then used with assumptions about the column abundance of NO to estimate surface fluxes of NOX. These results agreed in magnitude with results at Concordia Station and confirmed significant daily, intraseasonal and interannual variability in NO and its flux from the snow surface. Finally, we found that synoptic to mesoscale eddies governed the boundary layer circulation and accumulation pathways for NO at the South Pole rather than katabatic forcing. It was the small scale features of the circulation including the transition from cloudy to clear conditions that set the stage for short-term extremes in NO whereas larger-scale features were associated with more moderate concentrations.

scholarly journals High-Resolution In Situ Profiling through the Stable Boundary Layer: Examination of the SBL Top in Terms of Minimum Shear, Maximum Stratification, and Turbulence Decrease

2006 ◽  
Vol 63 (4) ◽  
pp. 1291-1307 ◽  
Author(s):  
B. B. Balsley ◽  
R. G. Frehlich ◽  
M. L. Jensen ◽  
Y. Meillier
Keyword(s):  
Boundary Layer ◽  
Energy Dissipation ◽  
High Resolution ◽  
Stable Boundary Layer ◽  
Dissipation Rate ◽  
Energy Dissipation Rate ◽  
Horizontal Wind ◽  
Small Scale ◽  
Stable Boundary ◽  
Stable Conditions

Abstract Some 50 separate high-resolution profiles of small-scale turbulence defined by the energy dissipation rate (ɛ), horizontal wind speed, and temperature from near the surface, through the nighttime stable boundary layer (SBL), and well into the residual layer are used to compare the various definitions of SBL height during nighttime stable conditions. These profiles were obtained during postmidnight periods on three separate nights using the Tethered Lifting System (TLS) during the Cooperative Atmosphere–Surface Exchange Study (CASES-99) campaign in east-central Kansas, October 1999. Although the number of profiles is insufficient to make any definitive conclusions, the results suggest that, under most conditions, the boundary layer top can be reasonably estimated in terms of a very significant decrease in the energy dissipation rate (i.e., the mixing height) with height. In the majority of instances this height lies slightly below the height of a pronounced minimum in wind shear and slightly above a maximum in N 2, where N is the Brunt–Väisälä frequency. When combined with flux measurements and vertical velocity variance data obtained from the nearby 55-m tower, the results provide additional insights into SBL processes, even when the boundary layer, by any definition, extends to heights well above the top of the tower. Both the TLS profiles and tower data are then used for preliminary high-resolution studies into various categories of SBL structure, including the so-called upside-down boundary layer.

scholarly journals Large-eddy simulation and stochastic modeling of Lagrangian particles for footprint determination in the stable boundary layer

2016 ◽  
Vol 9 (9) ◽  
pp. 2925-2949 ◽  
Author(s):  
Andrey Glazunov ◽  
Üllar Rannik ◽  
Victor Stepanenko ◽  
Vasily Lykosov ◽  
Mikko Auvinen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Stochastic Modeling ◽  
Stochastic Models ◽  
Stable Boundary Layer ◽  
Particle Dispersion ◽  
Small Scale ◽  
Stable Boundary ◽  
Eddy Simulation ◽  
Large Eddy

Abstract. Large-eddy simulation (LES) and Lagrangian stochastic modeling of passive particle dispersion were applied to the scalar flux footprint determination in the stable atmospheric boundary layer. The sensitivity of the LES results to the spatial resolution and to the parameterizations of small-scale turbulence was investigated. It was shown that the resolved and partially resolved (“subfilter-scale”) eddies are mainly responsible for particle dispersion in LES, implying that substantial improvement may be achieved by using recovering of small-scale velocity fluctuations. In LES with the explicit filtering, this recovering consists of the application of the known inverse filter operator. The footprint functions obtained in LES were compared with the functions calculated with the use of first-order single-particle Lagrangian stochastic models (LSMs) and zeroth-order Lagrangian stochastic models – the random displacement models (RDMs). According to the presented LES, the source area and footprints in the stable boundary layer can be substantially more extended than those predicted by the modern LSMs.

scholarly journals Large-eddy simulation and stochastic modelling of Lagrangian particles for footprint determination in stable boundary layer

2016 ◽  
Author(s):  
Andrey Glazunov ◽  
Üllar Rannik ◽  
Victor Stepanenko ◽  
Vasily Lykosov ◽  
Ivan Mammarella ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Stochastic Models ◽  
Stable Boundary Layer ◽  
Stochastic Modelling ◽  
Particle Dispersion ◽  
Small Scale ◽  
Stable Boundary ◽  
Eddy Simulation ◽  
Large Eddy

Abstract. Large-eddy simulation (LES) and Lagrangian stochastic modelling of passive particle dispersion were applied to the scalar flux footprint determination in stable atmospheric boundary layer. The sensitivity of the LES results to the spatial resolution and to the parameterizations of small-scale turbulence was investigated. It was shown that the resolved and partially resolved "subfilter-scale" eddies are mainly responsible for particle dispersion in LES, implying that substantial improvement may be achieved by using recovery of small-scale velocity fluctuations. In LES with the explicit filtering this recovering consists of application of the known inverse filter operator. The footprint functions obtained in LES were compared with the functions calculated with the use of first-order single particle Lagrangian stochastic models (LSM), zeroth-order Lagrangian stochastic models – the random displacement models (RDM), and analytical footprint parameterisations. It was observed that the value of the Kolmogorov constant C0 = 6 provided the best agreement of the one-dimensional LSMs results with LES, however, also that different LSMs can produce quite different footprint predictions. According to presented LES the source area and footprints in stable boundary layer can be substantially more extended than those predicted by the modern analytical footprint parameterizations and LSMs.

Wave Drag and Form Drag Induced by Small Scale Terrain in the Nocturnal Stable Boundary Layer

2007 ◽  
Vol 50 (1) ◽  
pp. 41-50 ◽  
Author(s):  
Yu-Jun JIANG ◽  
Jian-Guo SANG ◽  
Hui-Zhi LIU ◽  
Shu-Hua LIU
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Wave Drag ◽  
Small Scale ◽  
Form Drag ◽  
Stable Boundary

Stable Boundary Layer Regimes in Single-Column Models

2020 ◽  
Vol 77 (6) ◽  
pp. 2039-2054 ◽  
Author(s):  
Felipe D. Costa ◽  
Otávio C. Acevedo ◽  
Luiz E. Medeiros ◽  
Rafael Maroneze ◽  
Franciano S. Puhales ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Stable Boundary Layer ◽  
Layer Structure ◽  
Stable Layer ◽  
Stable Boundary ◽  
Stability Functions ◽  
Single Column ◽  
Mean Wind Speed ◽  
The Mean

Abstract Two contrasting flow regimes exist in the stable boundary layer (SBL), as evidenced from both observational and modeling studies. In general, numerical schemes such as those used in numerical weather prediction and climate models (NWPCs) reproduce a transition between SBL regimes. However, the characteristics of such a transition depend on the turbulence parameterizations and stability functions used to represent the eddy diffusivity in the models. The main goal of the present study is to detail how the two SBL regimes occur in single-column models (SCMs) by analyzing the SBL structure and its dependence on external parameters. Two different turbulence closure orders (first order and an E–l model) and two types of stability functions (short and long tail) are considered. The control exerted by the geostrophic wind and the surface cooling rate on the model SBL regimes is addressed. The model flow presents a three-layer structure: a fully turbulent, weakly stable layer (WSL) next to the surface; a very stable layer (VSL) above that; and a laminar layer above the other two and toward the domain top. It is shown that the WSL and VSL are related to both SBL regimes, respectively. Furthermore, the numerically simulated SBL presents the two-layer structure regardless of the turbulence parameterization order and stability function used. The models also reproduce other features reported in recent observational studies: an S-shaped dependence of the thermal gradient on the mean wind speed and an independence of the vertical gradient of friction velocity δu* on the mean wind speed.

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