An Observational, Spatially Explicit, Stability-Based Estimate of the Wind Resource off the Shore of North Carolina

AbstractAs part of ongoing studies of the feasibility of utility-scale wind energy off the shore of North Carolina, winds at 80-m elevation are estimated with a stability-based height-adjustment scheme. Data sources are level-3 daily Advanced Scatterometer (ASCAT) 10-m wind fields as measured by the MetOp-A satellite, North American Regional Reanalysis (NARR) estimates of near-surface atmospheric temperature and humidity, and the National Climatic Data Center’s optimally interpolated Advanced Very High Resolution Radiometer (AVHRR-OI) sea surface temperature (SST). A height-adjustment assuming neutral atmospheric stability provides reference conditions. The SST from AVHRR-OI was more accurate than SST from NARR and was used with NARR atmospheric data to represent atmospheric stability in the study region. The 5-yr average of the ASCAT 10-m winds is 6.5–9.0 m s−1 off the shore of North Carolina, with the strongest winds found over the Gulf Stream. Neutral-scheme 80-m wind speeds are 7.5–10.5 m s−1 and follow the same spatial pattern. The stability-based scheme produces an 80-m wind field with significantly different spatial wind patterns, with greater wind speeds than the neutral scheme in coastal regions where stable atmosphere conditions occur and lesser wind speeds than the neutral scheme farther offshore where unstable conditions are prevalent. The largest differences between the schemes occur in winter and spring when and where stable atmospheric conditions are most common. Estimated power inshore from the 100-m isobath with the neutral scheme yields average values of 400–800 W m−2, whereas the stability-based-scheme values are 600–800 W m−2. Capacity factors vary between 30% and 55%, with values in excess of 40% common in coastal areas off North Carolina.

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Examination of Errors in Near-Surface Temperature and Wind from WRF Numerical Simulations in Regions of Complex Terrain

Weather and Forecasting ◽

10.1175/waf-d-12-00109.1 ◽

2013 ◽

Vol 28 (3) ◽

pp. 893-914 ◽

Cited By ~ 90

Author(s):

Hailing Zhang ◽

Zhaoxia Pu ◽

Xuebo Zhang

Keyword(s):

Complex Terrain ◽

Forecast Error ◽

Wrf Model ◽

Atmospheric Temperature ◽

Lower Atmosphere ◽

Forecast Errors ◽

Atmospheric Conditions ◽

Near Surface ◽

System A ◽

Synoptic Forcing

Abstract The performance of an advanced research version of the Weather Research and Forecasting Model (WRF) in predicting near-surface atmospheric temperature and wind conditions under various terrain and weather regimes is examined. Verification of 2-m temperature and 10-m wind speed and direction against surface Mesonet observations is conducted. Three individual events under strong synoptic forcings (i.e., a frontal system, a low-level jet, and a persistent inversion) are first evaluated. It is found that the WRF model is able to reproduce these weather phenomena reasonably well. Forecasts of near-surface variables in flat terrain generally agree well with observations, but errors also occur, depending on the predictability of the lower-atmospheric boundary layer. In complex terrain, forecasts not only suffer from the model's inability to reproduce accurate atmospheric conditions in the lower atmosphere but also struggle with representative issues due to mismatches between the model and the actual terrain. In addition, surface forecasts at finer resolutions do not always outperform those at coarser resolutions. Increasing the vertical resolution may not help predict the near-surface variables, although it does improve the forecasts of the structure of mesoscale weather phenomena. A statistical analysis is also performed for 120 forecasts during a 1-month period to further investigate forecast error characteristics in complex terrain. Results illustrate that forecast errors in near-surface variables depend strongly on the diurnal variation in surface conditions, especially when synoptic forcing is weak. Under strong synoptic forcing, the diurnal patterns in the errors break down, while the flow-dependent errors are clearly shown.

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Wind tunnel experiments: cold-air pooling and atmospheric decoupling above a melting snow patch

The Cryosphere ◽

10.5194/tc-10-445-2016 ◽

2016 ◽

Vol 10 (1) ◽

pp. 445-458 ◽

Cited By ~ 8

Author(s):

Rebecca Mott ◽

Enrico Paterna ◽

Stefan Horender ◽

Philip Crivelli ◽

Michael Lehning

Keyword(s):

Wind Tunnel ◽

Atmospheric Stability ◽

Strong Stability ◽

Snow Surface ◽

Near Surface ◽

Cold Air ◽

Melting Snow ◽

Ambient Flow ◽

Wind Speeds ◽

Two Factors

Abstract. The longevity of perennial snowfields is not fully understood, but it is known that strong atmospheric stability and thus boundary-layer decoupling limit the amount of (sensible and latent) heat that can be transmitted from the atmosphere to the snow surface. The strong stability is typically caused by two factors, (i) the temperature difference between the (melting) snow surface and the near-surface atmosphere and (ii) cold-air pooling in topographic depressions. These factors are almost always a prerequisite for perennial snowfields to exist. For the first time, this contribution investigates the relative importance of the two factors in a controlled wind tunnel environment. Vertical profiles of sensible heat and momentum fluxes are measured using two-component hot-wire and one-component cold-wire anemometry directly over the melting snow patch. The comparison between a flat snow surface and one that has a depression shows that atmospheric decoupling is strongly increased in the case of topographic sheltering but only for low to moderate wind speeds. For those conditions, the near-surface suppression of turbulent mixing was observed to be strongest, and the ambient flow was decoupled from the surface, enhancing near-surface atmospheric stability over the single snow patch.

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Very short-term forecast of near-coastal flow using scanning lidars

10.5194/wes-2017-48 ◽

2017 ◽

Author(s):

Laura Valldecabres ◽

Alfredo Peña ◽

Michael Courtney ◽

Lueder von Bremen ◽

Martin Kühn

Keyword(s):

Arima Model ◽

Atmospheric Stability ◽

Lead Times ◽

Atmospheric Conditions ◽

Short Term ◽

Wind Speeds ◽

Lidar Measurements ◽

Wind Measurements ◽

Scanning Lidar ◽

Coastal Flow

Abstract. Wind measurements can reduce the uncertainty in the prediction of wind energy production. Nowadays, commercially available scanning lidars can scan the atmosphere up to several kilometres. Here, we use lidar measurements to forecast near-coastal winds with lead times of five minutes. Using Taylor's frozen turbulence hypothesis together with local topographic corrections, we demonstrate that wind speeds at a downstream position can be forecast by using measurements from a scanning lidar performed upstream in a very short-term horizon. The study covers ten periods characterized by neutral and stable atmospheric conditions. Our methodology shows smaller forecasting errors than those of the persistence method and the ARIMA model. We discuss the applicability of this forecasting technique with regards to the characteristics of the lidar trajectories, the site-specific conditions and the atmospheric stability.

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The Role of Atmospheric Stability and Turbulence in Offshore Wind-Farm Wakes in the German Bight

Boundary-Layer Meteorology ◽

10.1007/s10546-021-00668-4 ◽

2021 ◽

Author(s):

Andreas Platis ◽

Marie Hundhausen ◽

Astrid Lampert ◽

Stefan Emeis ◽

Jens Bange

Keyword(s):

German Bight ◽

Wind Farm ◽

Atmospheric Stability ◽

Wind Farms ◽

Offshore Wind ◽

Lapse Rate ◽

Offshore Wind Farm ◽

Near Surface ◽

Stable Conditions ◽

The Stability

AbstractAirborne meteorological in situ measurements as well as stationary measurements at the offshore masts FINO1 and FINO3 in the German Bight are evaluated in order to examine the hypothesis that the wake dissipation downstream of large offshore wind farms depends on atmospheric stability. A long-term study of the mast data for the years 2016 and 2017 demonstrates a clear dependence of stability on the wind direction. Stable conditions are predominantly expected during southerly winds coming from the land. The analysis of various stability and turbulence criteria shows that the lapse rate is the most robust parameter for stability classification in the German Bight, but further implies that stability depends on the measurement height. A near-surface (0 to 30 m), predominantly convective, layer is present and more stable conditions are found aloft (55 to 95 m). Combing the stability data with the airborne measurements of the offshore wind-farm wakes reveals the trend of a correlation between longer wake lengths and an increase in the initial wind-speed deficit downwind of a wind farm with stronger thermal stability. However, the stability correlation criteria with the wake length downstream of the four investigated wind farms, Godewind, Amrumbank West, Meerwind Süd/Ost, and Nordsee Ost, contain large variance. It is assumed that the observed scattering is due to the influence of the wind-farm architecture and temperature inversions around hub height. These, however, are crucial for the classification of stability and illustrate the complexity of a clear stability metric.

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The Daily Cycle of Low-Frequency Elephant Calls and Near-Surface Atmospheric Conditions

Earth Interactions ◽

10.1175/ei147.1 ◽

2005 ◽

Vol 9 (14) ◽

pp. 1-21 ◽

Cited By ~ 12

Author(s):

Michael Garstang ◽

David R. Fitzjarrald ◽

Kurt Fristrup ◽

Conrad Brain

Keyword(s):

National Park ◽

Atmospheric Stability ◽

Low Frequency ◽

Bimodal Distribution ◽

Dry Season ◽

Acoustic Model ◽

Atmospheric Conditions ◽

Daily Cycle ◽

Near Surface ◽

Secondary Maximum

Abstract Elephant low-frequency calls and atmospheric conditions that influence the transmission and detection of these calls were recorded at a fixed location over a period of about 3 weeks at the end of the dry season in the Etosha National Park, Namibia. A bimodal distribution in elephant call detections is observed, with the primary maximum (42% of all calls) occurring in a 3-h period following sunset and a secondary maximum (29% of all calls) in a 2-h period following sunrise. This distribution in calls detected is shown to depend upon marked and regular changes over 24 h in near-surface atmospheric stability and velocity, which determine propagation ranges. The observed bimodal distribution of calls detected depends upon these changes in atmospheric conditions as well as the location of the caller and the rate of calling. The findings are supported by results from an atmospheric acoustic model but are at variance with observations of the number of calls made from collared elephants in markedly different habitat. Detection of calls heard at a location remote from the caller represents a valuable and noninvasive research and applied tool that, however, must take note of atmospheric conditions that govern the propagation and reception of such signals.

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The Influence of a Lake-to-Lake Connection from Lake Huron on the Lake-Effect Snowfall in the Vicinity of Lake Ontario

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-17-0225.1 ◽

2018 ◽

Vol 57 (7) ◽

pp. 1423-1439 ◽

Cited By ~ 3

Author(s):

Carrie E. Lang ◽

Jessica M. McDonald ◽

Lauriana Gaudet ◽

Dylan Doeblin ◽

Erin A. Jones ◽

...

Keyword(s):

New York ◽

New York State ◽

Lake Ontario ◽

Heat Fluxes ◽

Lake Huron ◽

Atmospheric Conditions ◽

Near Surface ◽

Surface Heat Fluxes ◽

Wind Speeds ◽

Lake Effect

AbstractLake-effect storms (LES) produce substantial snowfall in the vicinity of the downwind shores of the Great Lakes. These storms may take many forms; one type of LES event, lake to lake (L2L), occurs when LES clouds/snowbands develop over an upstream lake (e.g., Lake Huron), extend across an intervening landmass, and continue over a downstream lake (e.g., Lake Ontario). The current study examined LES snowfall in the vicinity of Lake Ontario and the atmospheric conditions during Lake Huron-to-Lake Ontario L2L days as compared with LES days on which an L2L connection was not present [i.e., only Lake Ontario (OLO)] for the cold seasons (October–March) from 2003/04 through 2013/14. Analyses of snowfall demonstrate that, on average, significantly greater LES snowfall totals occur downstream of Lake Ontario on L2L days than on OLO days. The difference in mean snowfall between L2L and OLO days approaches 200% in some areas near the Tug Hill Plateau and central New York State. Analyses of atmospheric conditions found more-favorable LES environments on L2L days relative to OLO days that included greater instability over the upwind lake, more near-surface moisture available, faster wind speeds, and larger surface heat fluxes over the upstream lake. Last, despite significant snowfalls on L2L days, their average contribution to the annual accumulated LES snowfall in the vicinity of Lake Ontario was found to be small (i.e., 25%–30%) because of the relatively infrequent occurrence of L2L days.

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Ozone deposition to a coastal sea: comparison of eddy covariance observations with reactive air–sea exchange models

Atmospheric Measurement Techniques ◽

10.5194/amt-13-6915-2020 ◽

2020 ◽

Vol 13 (12) ◽

pp. 6915-6931

Author(s):

David C. Loades ◽

Mingxi Yang ◽

Thomas G. Bell ◽

Adam R. Vaughan ◽

Ryan J. Pound ◽

...

Keyword(s):

Wind Speed ◽

Eddy Covariance ◽

Friction Velocity ◽

Limit Of Detection ◽

Deposition Velocity ◽

Atmospheric Stability ◽

Layer Model ◽

Near Surface ◽

Wind Speeds ◽

Ozone Deposition

Abstract. A fast-response (10 Hz) chemiluminescence detector for ozone (O3) was used to determine O3 fluxes using the eddy covariance technique at the Penlee Point Atmospheric Observatory (PPAO) on the south coast of the UK during April and May 2018. The median O3 flux was −0.132 mg m−2 h−1 (0.018 ppbv m s−1), corresponding to a deposition velocity of 0.037 cm s−1 (interquartile range 0.017–0.065 cm s−1) – similar to the higher values previously reported for open-ocean flux measurements but not as high as some other coastal results. We demonstrate that a typical single flux observation was above the 2σ limit of detection but had considerable uncertainty. The median 2σ uncertainty of deposition velocity was 0.031 cm s−1 for each 20 min period, which reduces with the square root of the sample size. Eddy covariance footprint analysis of the site indicates that the flux footprint was predominantly over water (> 96 %), varying with atmospheric stability and, to a lesser extent, with the tide. At very low wind speeds when the atmosphere was typically unstable, the observed ozone deposition velocity was elevated, most likely because the footprint contracted to include a greater land contribution in these conditions. At moderate to high wind speeds when atmospheric stability was near-neutral, the ozone deposition velocity increased with wind speed and showed a linear dependence with friction velocity. This observed dependence on friction velocity (and therefore also wind speed) is consistent with the predictions from the one-layer model of Fairall et al. (2007), which parameterises the oceanic deposition of ozone from the fundamental conservation equation, accounting for both ocean turbulence and near-surface chemical destruction, while assuming that chemical O3 destruction by iodide is distributed over depth. In contrast to our observations, the deposition velocity predicted by the recently developed two-layer model of Luhar et al. (2018) (which considers iodide reactivity in both layers but with molecular diffusivity dominating over turbulent diffusivity in the first layer) shows no major dependence of deposition velocity on wind speed and underestimates the measured deposition velocities. These results call for further investigation into the mechanisms and control of oceanic O3 deposition.

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Diminishing Arctic Sea Ice Promotes Stronger Surface Winds

Journal of Climate ◽

10.1175/jcli-d-18-0109.1 ◽

2018 ◽

Vol 31 (19) ◽

pp. 8101-8119 ◽

Cited By ~ 11

Author(s):

John Mioduszewski ◽

Stephen Vavrus ◽

Muyin Wang

Keyword(s):

Surface Roughness ◽

Sea Ice ◽

Surface Wind ◽

Atmospheric Stability ◽

Arctic Sea Ice ◽

The Arctic ◽

Near Surface ◽

Wind Speeds ◽

Arctic Sea ◽

Autumn And Winter

Projections of Arctic sea ice through the end of the twenty-first century indicate the likelihood of a strong reduction in ice area and thickness in all seasons, leading to a substantial thermodynamic influence on the overlying atmosphere. This is likely to have an effect on winds over the Arctic basin because of changes in atmospheric stability, surface roughness, and/or baroclinicity. Here we identify patterns of wind changes in all seasons across the Arctic and their likely causal mechanisms, particularly those associated with sea ice loss. Output from the Community Earth System Model Large Ensemble Project (CESM-LE) was analyzed for the recent past (primarily 1971–2000) and future (2071–2100). Mean near-surface wind speeds over the Arctic Ocean are projected to increase by late century in all seasons but especially during autumn and winter, when they strengthen by up to 50% locally. The most extreme wind speeds in the 95th percentile change even more, increasing in frequency by up to 100%. The strengthened winds are closely linked to decreasing surface roughness and lower-tropospheric stability resulting from the loss of sea ice cover and consequent surface warming (exceeding 20°C warmer in the central Arctic in autumn and winter), as well as local changes in the storm track. The implications of stronger future winds include increased coastal and navigational hazards. Our findings suggest that increasing winds, along with reduction of sea ice, rising sea level, and thawing permafrost, represent another important contributor to the growing problem of Arctic coastal erosion.

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Melt and surface sublimation across a glacier in a dry environment: distributed energy-balance modelling of Juncal Norte Glacier, Chile

Journal of Glaciology ◽

10.1017/jog.2017.46 ◽

2017 ◽

Vol 63 (241) ◽

pp. 803-822 ◽

Cited By ~ 11

Author(s):

A. AYALA ◽

F. PELLICCIOTTI ◽

N. PELEG ◽

P. BURLANDO

Keyword(s):

Surface Air Temperature ◽

Spatial Variations ◽

Distributed Energy ◽

Physical Processes ◽

Summer Period ◽

Study Region ◽

Near Surface ◽

Wind Speeds ◽

Glacier Terminus ◽

Mass Fluxes

ABSTRACTPrevious estimates of melt and surface sublimation on glaciers of the subtropical semiarid Andes (29–34°S) have been obtained at few specific locations, but it is not clear how ablation components vary across the entire extent of a glacier in this dry environment. Here, we simulate the distributed energy and mass balance of Juncal Norte Glacier (33°S) during a 2-month summer period. Forcing fields of near-surface air temperature and wind speed are generated using two methods accounting for the main physical processes that shape their spatial variations. Simulated meteorological variables and ablation agree well with observations on the glacier tongue and reveal complex patterns of energy and mass fluxes. Ablation decreases from 70 mm w.e. d−1 at the low-albedo glacier terminus (~3000 m), where almost 100% of total ablation corresponds to melt, to <5 mm w.e. d−1 at wind-exposed, strong-radiated sites above 5500 m, where surface sublimation represents >75% of total ablation. Our simulations provide the first glacier-scale estimates of ablation components on a glacier in the study region and better reproduce the observed and expected spatial variations of melt and surface sublimation, in comparison with more simple assumptions, such as linear gradients and uniform wind speeds.

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Wind tunnel experiments: cold-air pooling and atmospheric decoupling above a melting snow patch

The Cryosphere Discussions ◽

10.5194/tcd-9-5413-2015 ◽

2015 ◽

Vol 9 (5) ◽

pp. 5413-5443

Author(s):

R. Mott ◽

E. Paterna ◽

S. Horender ◽

P. Crivelli ◽

M. Lehning

Keyword(s):

Wind Tunnel ◽

Atmospheric Stability ◽

Strong Stability ◽

Heat Fluxes ◽

Snow Surface ◽

Near Surface ◽

Cold Air ◽

Melting Snow ◽

Wind Speeds ◽

Two Factors

Abstract. The longevity of perennial snow fields is not fully understood but it is known that strong atmospheric stability and thus boundary layer decoupling limits the amount of (sensible and latent) heat that can be transmitted to the snow surface. The strong stability is typically caused by two factors, (i) the temperature difference between the (melting) snow surface and the near-surface atmosphere and (ii) cold-air pooling in topographic depressions. These factors are almost always a prerequisite for perennial snow fields to exist. For the first time, this contribution investigates the relative importance of the two factors in a controlled wind tunnel environment. Vertical profiles of sensible heat fluxes are measured using two-component hot wire and one-component cold-wire anemometry directly over the melting snow patch. The comparison between a flat snow surface and one that has a depression shows that atmospheric decoupling is strongly increased in the case of topographic sheltering but only for low to moderate wind speeds. For those conditions, the near-surface suppression of turbulent mixing was observed to be strongest and drainage flows were decoupled from the surface enhancing atmospheric stability and promoting the cold-air pooling over the single snow patch. Further work is required to systematically and quantitatively describe the flux distribution for varying terrain geometry, wind speeds and air temperatures.

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