Laboratory of Atmospheric Microphysics and Radiation (LAMAR): a set of sensors for the study of extreme meteorological events in the Central Andes of Peru.

2020 ◽  
Author(s):  
Daniel Martinez ◽  
Yamina Silva ◽  
Rene Estevan ◽  
Jose Luis Flores ◽  
Luis Suarez ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Flows ◽  
Solar Irradiance ◽  
Central Andes ◽  
Surface Energy Budget ◽  
Radiative Properties ◽  
Wind Profiler ◽  
Surface Boundary ◽  
Near Surface ◽  
Practical Applications

<p>A set of instruments to measure several atmospheric physical, microphysical and radiative properties of the atmosphere and clouds is essential to understand the conditions of formation and development, and eventually, the effects of extreme meteorological events, like severe rainfall, hailstorms and frost events that occur with some regularity in the central Andes of Peru. With this purpose, the Geophysical Institute of Peru has installed a set of specialized sensors in the Huancayo observatory (12.04°S,75.32°W, 3313 m ASL)  including  sub-sets dedicated to the measurements of near-surface and low boundary layer turbulent flows (turbulence and gradients subset),  measurement of precipitation and its structure (precipitation subset)and the measurement of aerosols and their interaction with radiation in the atmosphere (radiation subset). Additionally, a proper open area is reserved for  upper air soundings.  The turbulence subset consists of a set of thermohygrometers (HMP60 probe of Campbell Scientific) placed in two towers, one of 1 m and another of 30 m high, two wind sentry sets (03002 of Campbell Scientific), five tensiometers (Decagon 5TM VWC) to measure soil temperatures and moistures and a soil heat flux plate (HFP01 of Campbell scientific). The radiation subset consists of three pyranometers (CMP10 of Kipp & Zonen), to measure short-wave solar irradiance components, for(global, diffuse and reflected) and a pyrheliometer (CHP1 of Kipp & Zonen) to measure direct solar irradiance. A small black sphere mounted on an articulated shading assembly in a two-axis automatic sun tracker (Kipp & Zonen 2AP) blocked direct solar irradiance and allows to measure diffuse solar irradiance. To measure long-wave terrestrial irradiance components, two pyrgeometers are used (CGR4 of Kipp & Zonen). All these radiative sensors are installed in a tower of 6 m high. The precipitation subset includes A Ka-band cloud profiler (MIRA-35c), a disdrometer (PARSIVEL2) and two rain gauges pluviometers. A UHF wind profiler (CLAIRE), and a VHF wind profiler (BLTR) complement the precipitation subset, as they can detect turbulent low-level wind turbulence, associated with precipitation events.  . The upper-air sounding system consists of two stations: Windsond, for  model S1H3) and Meteo-modem, for model M10 radiosondes. All these sensors have been used to study the surface-atmosphere interactions, including the behavior of surface boundary layer, the components of surface energy budget and the microphysics properties or rainfall during the occurrence of extreme meteorological events, and to validate numerical model simulations. To show practical applications of LAMAR instrumentation we present a detailed analysis of two events: a severe rainfall event occurred on 17 January 2018 and a frost event occurred on 08 July 2018.</p>

scholarly journals Implementation of a boundary layer heat flux parameterization into the Regional Atmospheric Modeling System (RAMS)

2008 ◽  
Vol 8 (4) ◽  
pp. 14311-14346 ◽  
Author(s):  
E. L. McGrath-Spangler ◽  
A. S. Denning ◽  
K. D. Corbin ◽  
I. T. Baker
Keyword(s):  
Carbon Dioxide ◽  
Boundary Layer ◽  
Heat Flux ◽  
Lower Layer ◽  
Bowen Ratio ◽  
Surface Flux ◽  
Atmospheric Modeling ◽  
Surface Energy Budget ◽  
Stress Factors ◽  
Surface Boundary

Abstract. The response of atmospheric carbon dioxide to a given amount of surface flux is inversely proportional to the depth of the boundary layer. Overshooting thermals that entrain free tropospheric air down into the boundary layer modify the characteristics and depth of the lower layer through the insertion of energy and mass. This alters the surface energy budget by changing the Bowen ratio and thereby altering the vegetative response and the surface boundary conditions. Although overshooting thermals are important in the physical world, their effects are unresolved in most regional models. A parameterization to include the effects of boundary layer entrainment was introduced into a coupled ecosystem-atmosphere model (SiB-RAMS). The parameterization is based on a downward heat flux at the top of the boundary layer that is proportional to the heat flux at the surface. Results with the parameterization show that the boundary layer simulated is deeper, warmer, and drier than when the parameterization is turned off. These results alter the vegetative stress factors thereby changing the carbon flux from the surface. The combination of this and the deeper boundary layer change the concentration of carbon dioxide in the boundary layer.

Mountain Meteorology

Geography ◽  
2019 ◽  
Author(s):  
Brandon Vogt, PhD
Keyword(s):  
Boundary Layer ◽  
Land Surface ◽  
Reverse Direction ◽  
Surface Boundary ◽  
Science Literature ◽  
Fine Scale ◽  
Mountain Meteorology ◽  
Near Surface ◽  
Atmospheric Motion ◽  
Temperature Inversions

Meteorology is the science that examines the configuration of fundamental weather elements in Earth’s atmosphere: pressure, temperature, humidity, wind, precipitation, and clouds. Weather defines the arrangement of these elements over short periods (minutes to days) and climate defines the average weather at a location over longer periods (months to centuries). Mountains cover roughly 25% of the Earth’s land surface and are home to about 12% of the world’s population. With innumerable topographic configurations, mountains disrupt airflow in the troposphere from the valley scale in the mountains themselves to hundreds of kilometers beyond their foothills. Atmospheric motion interacts with mountains via thermal and mechanical forces. Thermally, diurnal heating and cooling differences in complex terrain create circulating motions that reverse direction, day and night. Examples include fine-scale mountain and valley winds and more broad-scale anabatic and katabatic winds. Mechanically, disturbances and waves in atmospheric motion are forced upstream, downstream, above, and adjacent to mountains. Examples include blocking, upslope flow, downslope winds, gravity waves, boundary-layer turbulence, and lee cyclogenesis. Given the right atmospheric conditions, orographic processes generate extreme, damaging, and costly weather events such as strong Chinook/Föhn winds, heavy upslope snow events, steep terrain forcing in monsoon or atmospheric river flows, long-duration frigid valley temperature inversions, invisible lee rotors, and local zones of convergence that initiate strong convective thunderstorms. Finally, mountains create distinctive and often photographed clouds that include caps, lenticulars, and corrugations of standing waves. While the focus of this bibliography is weather, some atmosphere/landscape interactions, such as windward vs. leeward orographic effects, fall largely within climate science literature. Other more fine-scale interactions between the atmosphere and mountains, such as local shade effects and valley temperature inversions, are captured in planetary surface boundary layer topoclimate/microclimate literature. These near-surface processes influence the weather-making troposphere, and as such, are seamlessly tied to mountain meteorology. To build a robust context into this bibliography, select multiscalar climate-themed sources are identified. To glaciologists, atmospheric scientists (including forecasters), climatologists, ecologists, agricultural scientists, hydrologists, and others whose specializations operate in and adjacent to mountainous terrain, understanding the unique influences of mountains is essential. This article identifies key literature and other relevant sources that explore how mountains influence and modify weather, and to a lesser degree, climate. Together, these resources provide a rich set of teaching materials and a platform for more in-depth studies into mountain meteorology set in the context of geography.

scholarly journals Characteristics of the Near-Surface Boundary Layer within a Mountain Valley during Winter

2012 ◽  
Vol 51 (3) ◽  
pp. 583-597 ◽  
Author(s):  
Warren Helgason ◽  
John W. Pomeroy
Keyword(s):  
Boundary Layer ◽  
Heat Fluxes ◽  
Quadrant Analysis ◽  
Turbulent Heat ◽  
Surface Boundary ◽  
Wind Speed Profile ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Mountainous Regions ◽  
Mass Fluxes

AbstractWithin mountainous regions, estimating the exchange of sensible heat and water vapor between the surface and the atmosphere is an important but inexact endeavor. Measurements of the turbulence characteristics of the near-surface boundary layer in complex mountain terrain are relatively scarce, leading to considerable uncertainty in the application of flux-gradient techniques for estimating the surface turbulent heat and mass fluxes. An investigation of the near-surface boundary layer within a 7-ha snow-covered forest clearing was conducted in the Kananaskis River valley, located within the Canadian Rocky Mountains. The homogeneous measurement site was characterized as being relatively calm and sheltered; the wind exhibited considerable unsteadiness, however. Frequent wind gusts were observed to transport turbulent energy into the clearing, affecting the rate of energy transfer at the snow surface. The resulting boundary layer within the clearing exhibited perturbations introduced by the surrounding topography and land surface discontinuities. The measured momentum flux did not scale with the local aerodynamic roughness and mean wind speed profile, but rather was reflective of the larger-scale topographical disturbances. The intermittent nature of the flux-generating processes was evident in the turbulence spectra and cospectra where the peak energy was shifted to lower frequencies as compared with those observed in more homogeneous flat terrain. The contribution of intermittent events was studied using quadrant analysis, which revealed that 50% of the sensible and latent heat fluxes was contributed from motions that occupied less than 6% of the time. These results highlight the need for caution while estimating the turbulent heat and mass fluxes in mountain regions.

Fluid-Acoustics Interaction in Self-Sustained Oscillations Over a Cavity in a Turbulent Boundary Layer

2008 ◽  
Author(s):  
H. Yokoyama ◽  
C. Kato
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Layer Thickness ◽  
Turbulent Flows ◽  
Acoustic Waves ◽  
Boundary Layer Thickness ◽  
Stokes Equations ◽  
Practical Applications ◽  
Sustained Oscillations ◽  
Mach Numbers

Self-sustained oscillations with fluid-acoustics interaction over a cavity can radiate intense tonal sound and fatigue nearby components of industrial products. The prediction and the suppression of these oscillations are very important for many practical applications. However, the fluid-acoustics interaction has not been thoroughly clarified in particular for the oscillations in turbulent flows. We investigate the mechanism of the oscillations over a rectangular cavity with a length-to-depth ratio of 2:1 by directly solving the compressible Navier-Stokes equations. The boundary layer over the cavity is turbulent and the freestream Mach numbers are M = 0.4 and 0.7. The results clarify that the self-sustained oscillations occur in the shear layer of the cavity and the oscillations are reinforced by the streamwise acoustic mode in the cavity for both Mach numbers. The shear layer of the cavity undulates. This undulation causes the deformation of fine vortices in the shear layer and radiates acoustic waves from the downstream edge of the cavity. Also, we clarify by the conditional identification of longitudinal vortices that the acoustic waves cause the undulation of the shear layer and a feedback loop is formed. Moreover, the comparison of the flow field over the cavity with that over a simple backstep shows that the shear layer in the cavity becomes two-dimensional by the acoustic feedback. Finally, we show that the oscillations become weaker particularly at M = 0.4 and the frequencies of the oscillations become lower as the boundary layer thickness at the upstream edge of the cavity increases. Considering this effect of the boundary layer thickness, the peak frequencies predicted by our computations are in good agreement with those measured in a past experiment.

scholarly journals Measurements of Enhanced Near-Surface Turbulence under Windrows

2020 ◽  
Vol 50 (1) ◽  
pp. 197-215
Author(s):  
Seth F. Zippel ◽  
Ted Maksym ◽  
Malcolm Scully ◽  
Peter Sutherland ◽  
Dany Dumont
Keyword(s):  
Boundary Layer ◽  
Surface Flux ◽  
Breaking Waves ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Surface Turbulence ◽  
Order Of Magnitude ◽  
Convergence Zones ◽  
Shallow Bay

AbstractObservations of waves, winds, turbulence, and the geometry and circulation of windrows were made in a shallow bay in the winter of 2018 outside of Rimouski, Québec. Water velocities measured from a forward-looking pulse-coherent ADCP mounted on a small zodiac show spanwise (cross-windrow) convergence, streamwise (downwind) velocity enhancement, and downwelling in the windrows, consistent with the view that windrows are the result of counterrotating pairs of wind-aligned vortices. The spacing of windrows, measured with acoustic backscatter and with surface imagery, was measured to be approximately twice the water depth, which suggests an aspect ratio of 1. The magnitude and vertical distribution of turbulence measured from the ADCP are consistent with a previous scaling and observations of near-surface turbulence under breaking waves, with dissipation rates larger and decaying faster vertically than what is expected from a shear-driven boundary layer. Measurements of dissipation rate are partitioned to within, and outside of the windrow convergence zones, and measurements inside the convergence zones are found to be nearly an order of magnitude larger than those outside with similar vertical structure. A ratio of time scales suggests that turbulence likely dissipates before it can be advected horizontally into convergences, but the advection of wave energy into convergences may elevate the surface flux of TKE and could explain the elevated turbulence in the windrows. These results add to a limited number of conflicting observations of turbulence variability due to windrows, which may modify gas flux, and heat and momentum transport in the surface boundary layer.

scholarly journals The Three-Dimensional Structure and Evolution of a Tornado Boundary Layer

2013 ◽  
Vol 28 (6) ◽  
pp. 1552-1561 ◽  
Author(s):  
Karen A. Kosiba ◽  
Joshua Wurman
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Flow Region ◽  
Ground Level ◽  
Dimensional Structure ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Three Dimensional Structure ◽  
Flow Swirl

Abstract The finescale three-dimensional structure and evolution of the near-surface boundary layer of a tornado (TBL) is mapped for the first time. The multibeam Rapid-Scan Doppler on Wheels (RSDOW) collected data at several vertical levels, as low as 4, 6, 10, 12, 14, and 17 m above ground level (AGL), contemporaneously at 7-s intervals for several minutes in a tornado near Russell, Kansas, on 25 May 2012. Additionally, a mobile mesonet anemometer measured winds at 3.5 m AGL in the core flow region. The radar, anemometer, and ground-based velocity-track display (GBVTD) analyses reveal the peak wind intensity is very near the surface at ~5 m AGL, about 15% higher than at 10 m AGL and 25% higher than at ~40 m AGL. GBVTD analyses resolve a downdraft within the radius of maximum winds (RMW), which decreased in magnitude when varying estimates for debris centrifuging are included. Much of the inflow (from −1 to −7 m s−1) is at or below 10–14 m AGL, much shallower than reported previously. Surface outflow precedes tornado dissipation. Comparisons between large-eddy simulation (LES) predictions of the corner flow swirl ratio Sc and observed tornado intensity changes are consistent.

scholarly journals Parameterizations of Sea-Spray Impact on the Air–Sea Momentum and Heat Fluxes

2011 ◽  
Vol 139 (12) ◽  
pp. 3781-3797 ◽  
Author(s):  
J.-W. Bao ◽  
C. W. Fairall ◽  
S. A. Michelson ◽  
L. Bianco
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Weather Prediction ◽  
Heat Fluxes ◽  
Sea Spray ◽  
Surface Boundary ◽  
Near Surface ◽  
The Mean ◽  
Momentum And Heat Fluxes ◽  
The Impact

Abstract This paper focuses on parameterizing the effect of sea spray at hurricane-strength winds on the momentum and heat fluxes in weather prediction models using the Monin–Obukhov similarity theory (a common framework for the parameterizations of air–sea fluxes). In this scheme, the mass-density effect of sea spray is considered as an additional modification to the stratification of the near-surface profiles of wind, temperature, and moisture in the marine surface boundary layer (MSBL). The overall impact of sea-spray droplets on the mean profiles of wind, temperature, and moisture depends on the wind speed at the level of sea-spray generation. As the wind speed increases, the mean droplet size and the mass flux of sea-spray increase, rendering an increase of stability in the MSBL and the leveling-off of the surface drag. Sea spray also tends to increase the total air–sea sensible and latent heat fluxes at high winds. Results from sensitivity testing of the scheme in a numerical weather prediction model for an idealized case of hurricane intensification are presented along with a dynamical interpretation of the impact of the parameterized sea-spray physics on the structure of the hurricane boundary layer.

scholarly journals Baroclinic Frontal Instabilities and Turbulent Mixing in the Surface Boundary Layer. Part II: Forced Simulations

2017 ◽  
Vol 47 (10) ◽  
pp. 2429-2454 ◽  
Author(s):  
Eric D. Skyllingstad ◽  
Jenessa Duncombe ◽  
Roger M. Samelson
Keyword(s):  
Boundary Layer ◽  
Surface Wind ◽  
Vertical Mixing ◽  
Shear Instability ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Large Eddy Simulation Model ◽  
Geostrophic Balance ◽  
Geostrophic Shear

AbstractGeneration of ocean surface boundary layer turbulence and coherent roll structures is examined in the context of wind-driven and geostrophic shear associated with horizontal density gradients using a large-eddy simulation model. Numerical experiments over a range of surface wind forcing and horizontal density gradient strengths, combined with linear stability analysis, indicate that the dominant instability mechanism supporting coherent roll development in these simulations is a mixed instability combining shear instability of the ageostrophic, wind-driven flow with symmetric instability of the frontal geostrophic shear. Disruption of geostrophic balance by vertical mixing induces an inertially rotating ageostrophic current, not forced directly by the wind, that initially strengthens the stratification, damps the instabilities, and reduces vertical mixing, but instability and mixing return when the inertial buoyancy advection reverses. The resulting rolls and instabilities are not aligned with the frontal zone, with an oblique orientation controlled by the Ekman-like instability. Mean turbulence is enhanced when the winds are destabilizing relative to the frontal orientation, but mean Ekman buoyancy advection is found to be relatively unimportant in these simulations. Instead, the mean turbulent kinetic energy balance is dominated by mechanical shear production that is enhanced when the wind-driven shear augments the geostrophic shear, while the resulting vertical mixing nearly eliminates any effective surface buoyancy flux from near-surface, cold-to-warm, Ekman buoyancy advection.

scholarly journals Wind, Waves, and Fronts: Frictional Effects in a Generalized Ekman Model

2016 ◽  
Vol 46 (2) ◽  
pp. 371-394 ◽  
Author(s):  
Jacob O. Wenegrat ◽  
Michael J. McPhaden
Keyword(s):  
Boundary Layer ◽  
Surface Waves ◽  
Ocean Currents ◽  
Surface Boundary ◽  
Pressure Gradients ◽  
Surface Boundary Layer ◽  
Near Surface ◽  
Thermal Wind ◽  
Surface Ocean ◽  
Wide Range

AbstractOcean currents in the surface boundary layer are sensitive to a variety of parameters not included in classic Ekman theory, including the vertical structure of eddy viscosity, finite boundary layer depth, baroclinic pressure gradients, and surface waves. These parameters can modify the horizontal and vertical flow in the near-surface ocean, making them of first-order significance to a wide range of phenomena of broad practical and scientific import. In this work, an approximate Green’s function solution is found for a model of the frictional ocean surface boundary layer, termed the generalized Ekman (or turbulent thermal wind) balance. The solution admits consideration of general, more physically realistic forms of parameters than previously possible, offering improved physical insight into the underlying dynamics. Closed form solutions are given for the wind-driven flow in the presence of Coriolis–Stokes shear, a result of the surface wave field, and thermal wind shear, arising from a baroclinic pressure gradient, revealing the common underlying physical mechanisms through which they modify currents in the ocean boundary layer. These dynamics are further illustrated by a case study of an idealized two-dimensional front. The solutions, and estimates of the global distribution of the relative influence of surface waves and baroclinic pressure gradients on near-surface ocean currents, emphasize the broad importance of considering ocean sources of shear and physically realistic parameters in the Ekman problem.

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