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.

scholarly journals Seasonal and Diurnal Cycles of Surface Boundary Layer and Energy Balance in the Central Andes of Perú, Mantaro Valley

Atmosphere ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 779 ◽  
Author(s):  
José Luis Flores-Rojas ◽  
Joan Cuxart ◽  
Manuel Piñas-Laura ◽  
Stephany Callañaupa ◽  
Luis Suárez-Salas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Energy Balance ◽  
Bowen Ratio ◽  
Heat Fluxes ◽  
Surface Boundary ◽  
Sensible Heat ◽  
Surface Boundary Layer ◽  
Mountain Valley ◽  
Arid Conditions

The present study presents a detailed analysis of the diurnal and monthly cycles the surface boundary layer and of surface energy balance in a sparse natural vegetation canopy on Huancayo observatory (12.04 ∘ S, 75.32 ∘ W, 3313 m ASL), which is located in the central Andes of Perú (Mantaro Valley) during an entire year (May 2018–April 2019). We used a set of meteorological sensors (temperature, relative humidity, wind) installed in a gradient tower 30 m high, a set of radiative sensors to measure all irradiance components, and a set of tensiometers and heat flux plate to measure soil moisture, soil temperatures and soil heat flux. To estimate turbulent energy fluxes (sensible and latent), two flux–gradient methods: the aerodynamic method and the Bowen-ratio energy-balance method were used. The ground heat flux at surface was estimated using a molecular heat transfer equation. The results show minimum mean monthly temperatures and more stable conditions were observed in June and July before sunrise, while maximum mean monthly temperatures in October and November and more unstable conditions in February and March. From May to August inverted water vapor profiles near the surface were observed (more intense in July) at night hours, which indicate a transfer of water vapor as dewfall on the surface. The patterns of wind direction indicate well-defined mountain–valley circulation from south-east to south-west especially in fall–winter months (April–August). The maximum mean monthly sensible heat fluxes were found in June and September while minimum in February and March. Maximum mean monthly latent heat fluxes were found in February and March while minimum in June and July. The surface albedo and the Bowen ratio indicate semi-arid conditions in wet summer months and extreme arid conditions in dry winter months. The comparisons between sensible heat flux ( Q H ) and latent heat flux ( Q E ), estimated by the two methods show a good agreement (R 2 above 0.8). The comparison between available energy and the sum of Q E and Q H fluxes shows a good level of agreement (R 2 = 0.86) with important imbalance contributions after sunrise and around noon, probably by advection processes generated by heterogeneities on the surface around the Huancayo observatory and intensified by the mountain–valley circulation.

scholarly journals Surface flux estimates derived from UAS-based mole fraction measurements by means of a nocturnal boundary layer budget approach

2019 ◽  
Author(s):  
Martin Kunz ◽  
Jost V. Lavric ◽  
Rainer Gasche ◽  
Christoph Gerbig ◽  
Richard H. Grant ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Boundary Layer ◽  
Mole Fraction ◽  
Surface Flux ◽  
Nocturnal Boundary Layer ◽  
Carbon Dioxide Flux ◽  
Unmanned Aircraft ◽  
Atmospheric Conditions ◽  
Transport Modelling ◽  
Stable Conditions

Abstract. The carbon exchange between ecosystems and the atmosphere has a large influence on the Earth system and specifically on the climate. This exchange is therefore being studied intensively, often using the eddy covariance (EC) technique. EC measurements provide reliable results under turbulent atmospheric conditions, but under stable conditions – as they often occur at night – these measurements are known to misrepresent exchange fluxes. Nocturnal boundary layer (NBL) budgets can provide independent flux estimates under stable conditions, but their application so far has been limited by rather high cost and practical difficulties. Unmanned aircraft systems (UASs) equipped with trace gas analysers have the potential to make this method more accessible. We present the methodology and results of a proof of concept study carried out during the ScaleX 2016 campaign. Successive vertical profiles of carbon dioxide dry air mole fraction in the NBL were taken with a compact analyser carried by a UAS. We estimate an average carbon dioxide flux of 12 μmol m−2 s−1, which is plausible for nocturnal respiration in this region in summer. Transport modelling suggests that the NBL budgets represent an area on the order of 100 km2.

scholarly journals Downslope föhn winds over the Antarctic Peninsula and their effect on the Larsen ice shelves

2014 ◽  
Vol 14 (18) ◽  
pp. 9481-9509 ◽  
Author(s):  
D. P. Grosvenor ◽  
J. C. King ◽  
T. W. Choularton ◽  
T. Lachlan-Cope
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Surface Energy ◽  
Antarctic Peninsula ◽  
Energy Budget ◽  
Surface Flux ◽  
Surface Energy Budget ◽  
Ice Shelf ◽  
Aircraft Observations ◽  
The Antarctic

Abstract. Mesoscale model simulations are presented of a westerly föhn event over the Antarctic Peninsula mountain ridge and onto the Larsen C ice shelf, just south of the recently collapsed Larsen B ice shelf. Aircraft observations showed the presence of föhn jets descending near the ice shelf surface with maximum wind speeds at 250–350 m in height. Surface flux measurements suggested that melting was occurring. Simulated profiles of wind speed, temperature and wind direction were very similar to the observations. However, the good match only occurred at a model time corresponding to ~9 h before the aircraft observations were made since the model föhn jets died down after this. This was despite the fact that the model was nudged towards analysis for heights greater than ~1.15 km above the surface. Timing issues aside, the otherwise good comparison between the model and observations gave confidence that the model flow structure was similar to that in reality. Details of the model jet structure are explored and discussed and are found to have ramifications for the placement of automatic weather station (AWS) stations on the ice shelf in order to detect föhn flow. Cross sections of the flow are also examined and were found to compare well to the aircraft measurements. Gravity wave breaking above the mountain crest likely created a~situation similar to hydraulic flow and allowed föhn flow and ice shelf surface warming to occur despite strong upwind blocking, which in previous studies of this region has generally not been considered. Our results therefore suggest that reduced upwind blocking, due to wind speed increases or stability decreases, might not result in an increased likelihood of föhn events over the Antarctic Peninsula, as previously suggested. The surface energy budget of the model during the melting periods showed that the net downwelling short-wave surface flux was the largest contributor to the melting energy, indicating that the cloud clearing effect of föhn events is likely to be the most important factor for increased melting relative to non-föhn days. The results also indicate that the warmth of the föhn jets through sensible heat flux ("SH") may not be critical in causing melting beyond boundary layer stabilisation effects (which may help to prevent cloud cover and suppress loss of heat by convection) and are actually cancelled by latent heat flux ("LH") effects (snow ablation). It was found that ground heat flux ("GRD") was likely to be an important factor when considering the changing surface energy budget for the southern regions of the ice shelf as the climate warms.

scholarly journals Surface Moistening Trends in the Northern North American Great Plains Increase the Likelihood of Convective Initiation

2018 ◽  
Vol 19 (1) ◽  
pp. 227-244 ◽  
Author(s):  
Tobias Gerken ◽  
Gabriel T. Bromley ◽  
Paul C. Stoy
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Atmospheric Boundary Layer ◽  
Great Plains ◽  
Land Management ◽  
Atmospheric Modeling ◽  
Convective Precipitation ◽  
Net Radiation ◽  
Modeling Framework ◽  
Summer Fallow

Abstract Land management impacts atmospheric boundary layer processes, and recent trends reducing the practice of summer fallow have led to increases in precipitation and decreases in temperature in the Canadian Prairie provinces during summer. It is unclear if such trends also impact the hydrometeorology of the adjacent U.S. northern Great Plains, parts of which have seen similar changes in land management. Here, MERRA-2 reanalysis data, eddy covariance observations, and a mixed-layer (ML) atmospheric modeling framework are combined to demonstrate that the likelihood of convectively preconditioned conditions has increased by approximately 10% since the mid-1980s and is now more sensitive to further decreases in the Bowen ratio (Bo) and maximum daily net radiation in northeastern Montana. Convective season Bo in the study area has decreased from approximately 2 to 1 from the 1980s until the present, largely due to simultaneous increases in latent heat flux and decreases in sensible heat flux, consistent with observed decreases of summer fallow and increases in cropping. Daily net radiation has not changed despite a significant decrease in May and June humidity lapse rates from the 1980s to present. Future research should determine the area of the U.S. Great Plains that has seen changes in the dynamics of the atmospheric boundary layer height and lifted condensation level and their crossings as a necessary condition for convective precipitation to occur and ascertain if ongoing changes in land management will lead to future changes in convective outcomes.

scholarly journals Surface flux estimates derived from UAS-based mole fraction measurements by means of a nocturnal boundary layer budget approach

2020 ◽  
Vol 13 (4) ◽  
pp. 1671-1692 ◽  
Author(s):  
Martin Kunz ◽  
Jost V. Lavric ◽  
Rainer Gasche ◽  
Christoph Gerbig ◽  
Richard H. Grant ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Boundary Layer ◽  
Mole Fraction ◽  
Surface Flux ◽  
Nocturnal Boundary Layer ◽  
Carbon Dioxide Flux ◽  
Unmanned Aircraft ◽  
Atmospheric Conditions ◽  
Transport Modelling ◽  
Stable Conditions

Abstract. The carbon exchange between ecosystems and the atmosphere has a large influence on the Earth system and specifically on the climate. This exchange is therefore being studied intensively, often using the eddy covariance (EC) technique. EC measurements provide reliable results under turbulent atmospheric conditions, but under calm and stable conditions – as they often occur at night – these measurements are known to misrepresent exchange fluxes. Nocturnal boundary layer (NBL) budgets can provide independent flux estimates under stable conditions, but their application so far has been limited by rather high cost and practical difficulties. Unmanned aircraft systems (UASs) equipped with trace gas analysers have the potential to make this method more accessible. We present the methodology and results of a proof-of-concept study carried out during the ScaleX 2016 campaign. Successive vertical profiles of carbon dioxide dry-air mole fraction in the NBL were taken with a compact analyser carried by a UAS. We estimate an average carbon dioxide flux of 12 µmolm-2s-1, which is plausible for nocturnal respiration in this region in summer. Transport modelling suggests that the NBL budgets represent an area on the order of 100 km2.

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 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 Impact of Surface Flux Formulations and Geostrophic Forcing on Large-Eddy Simulations of Diurnal Atmospheric Boundary Layer Flow

2010 ◽  
Vol 49 (7) ◽  
pp. 1496-1516 ◽  
Author(s):  
Vijayant Kumar ◽  
Gunilla Svensson ◽  
A. A. M. Holtslag ◽  
Charles Meneveau ◽  
Marc B. Parlange
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Boundary Conditions ◽  
Surface Temperature ◽  
Surface Flux ◽  
Large Eddy Simulations ◽  
Surface Boundary ◽  
Temperature Boundary ◽  
Large Eddy ◽  
Temperature Boundary Condition

Abstract The impact of surface flux boundary conditions and geostrophic forcing on multiday evolution of flow in the atmospheric boundary layer (ABL) was assessed using large-eddy simulations (LES). The LES investigations included several combinations of surface boundary conditions (temperature and heat flux) and geostrophic forcing (constant, time varying, time and height varying). The setup was based on ABL characteristics observed during a selected period of the Cooperative Atmosphere–Surface Exchange Study—1999 (CASES-99) campaign. The LES cases driven by a constant geostrophic wind achieved the best agreement with the CASES-99 observations specifically in terms of daytime surface fluxes and daytime and nighttime profiles. However, the nighttime fluxes were significantly overestimated. The LES cases with the surface temperature boundary condition and driven by a time- and height-varying geostrophic forcing showed improved agreement with the observed nighttime fluxes, but there was less agreement with other observations (e.g., daytime profiles). In terms of the surface boundary condition, the LES cases driven by either surface temperature or heat fluxes produced similar trends in terms of the daytime profiles and comparisons with data from soundings. However, in reproducing the fluxes and nighttime profiles, the agreement was better with imposed temperature because of its ability to interact dynamically with the air temperature field. Therefore, it is concluded that surface temperature boundary condition is better suited for simulations of temporally evolving ABL flow as in the diurnal evolution of the ABL.

scholarly journals Comparisons between Mean and Turbulent Parameters of Aircraft-Based and Ship-Based Measurements in the Marine Atmospheric Boundary Layer

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1088
Author(s):  
Min-Seong Kim ◽  
Byung Hyuk Kwon ◽  
Tae-Young Goo
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Atmospheric Boundary Layer ◽  
Radiation Flux ◽  
Sensible Heat Flux ◽  
Surface Flux ◽  
Marine Atmospheric Boundary Layer ◽  
The Mean ◽  
Good Agreement

The Structure des Echanges Mer-Atmosphère, Propriétés Océaniques/ Recherche Expérimentale (SEMAPHORE) experiment was conducted over the oceanic Azores current located in the Azores Basin. The evolution of the marine atmospheric boundary layer (MABL) was studied based on the evaluation of mean and turbulent data using in situ measurements by a ship and two aircrafts. The sea surface temperature (SST) field was characterized by a gradient of approximately 1 °C/100 km. The SST measured by aircraft decreased at a ratio of 0.25 °C/100 m of altitude due to the divergence of the infrared radiation flux from the surface. With the exception of temperature, the mean parameters measured by the two aircrafts were in good agreement with each other. The sensible heat flux was more dispersed than the latent heat flux according to the comparisons between aircraft and aircraft, and aircraft and ship. This study demonstrates the feasibility of using two aircraft to describe the MABL and surface flux with confidence.

scholarly journals Estimation of nocturnal CO<sub>2</sub> and N<sub>2</sub>O soil emissions using changes in surface boundary layer mass storage

2017 ◽  
Author(s):  
Richard H. Grant ◽  
Rex A. Omonode
Keyword(s):  
Carbon Dioxide ◽  
Boundary Layer ◽  
Trace Gases ◽  
Surface Boundary ◽  
Mass Storage ◽  
Surface Boundary Layer ◽  
Soil Emissions ◽  
Diffusive Fluxes ◽  
Carbon Dioxide Co2 ◽  
Mass Accumulation

Abstract. Abstract. Annual emissions of greenhouse and other trace gases requires knowledge of the emissions throughout the year. Unfortunately emissions into the surface boundary layer during stable, calm nocturnal periods are not measureable using most micrometeorological methods due to non-stationarity and uncoupled flow. However, during nocturnal periods with very light winds the concentration of carbon dioxide (CO2) and nitrous oxide (N2O) frequently accumulates near the surface and this mass accumulation can be used to determine emissions. Gas concentrations were measured at four heights (one within and three above canopy) and turbulence was measured at three heights above a mature 2.5 m high maize canopy from 23 July to 10 September 2015. Nocturnal CO2 and N2O fluxes from the canopy were determined using the accumulation of mass within a 6.3 m vertical domain of the nocturnal surface boundary layer. Diffusive fluxes out of the top of this domain were also estimated. Fluxes during near-calm nights (friction velocities

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