Intercomparison of Aircraft and Buoy Measurements of Wind and Wind Stress during SMILE*

Beardsley, Robert C.; Enriquez, Amelito G; Friehe, Carl A.; Alessi, Carol A.

doi:10.1175/1520-0426(1997)014<0969:ioaabm>2.0.co;2

Cited by 19 publications

(8 citation statements)

References 18 publications

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“…where C p is the specific heat of air, L y is the latent heat of vaporization of water, angle brackets indicate ensemble averages (assumed equivalent to time averages), and primes indicate turbulent quantities (i.e., u 0 [ u 2 hui). Covariance terms are calculated using integrated cospectra so that the behavior and quality of the covariance calculation can be investigated in frequency space (see, e.g., Friehe et al 1991;Beardsley et al 1997;Khelif et al 1999;French et al 2007). Examining the power spectra of relative wind components, we see a small peak around 28 Hz, coincident with a peak seen in the spectra of vertical velocity as measured by the IMU.…”

Section: Spectra and Flux Calculationsmentioning

confidence: 95%

Development and Testing of Instrumentation for UAV-Based Flux Measurements within Terrestrial and Marine Atmospheric Boundary Layers

Reineman

Lenain

Statom

et al. 2013

Journal of Atmospheric and Oceanic Technology

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Instrumentation packages have been developed for small (18–28 kg) unmanned aerial vehicles (UAVs) to measure momentum fluxes as well as latent, sensible, and radiative heat fluxes in the atmospheric boundary layer (ABL) and the topography below. Fast-response turbulence, hygrometer, and temperature probes permit turbulent momentum and heat flux measurements, and shortwave and longwave radiometers allow the determination of net radiation, surface temperature, and albedo. UAVs flying in vertical formation allow the direct measurement of fluxes within the ABL and, with onboard high-resolution visible and infrared video and laser altimetry, simultaneous observation of surface topography or ocean surface waves. The low altitude required for accurate flux measurements (typically assumed to be 30 m) is below the typical safety limit of manned research aircraft; however, with advances in laser altimeters, small-aircraft flight control, and real-time kinematic differential GPS, low-altitude flight is now within the capability of small UAV platforms. Flight tests of instrumented BAE Systems Manta C1 UAVs over land were conducted in January 2011 at McMillan Airfield (Camp Roberts, California). Flight tests of similarly instrumented Boeing Insitu ScanEagle UAVs were conducted in April 2012 at the Naval Surface Warfare Center, Dahlgren Division (Dahlgren, Virginia), where the first known measurements of water vapor, heat, and momentum fluxes were made from low-altitude (down to 30 m) UAV flights over water (Potomac River). This study presents a description of the instrumentation, summarizes results from flight tests, and discusses potential applications of these UAVs for (marine) atmospheric boundary layer studies.

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Section: Spectra and Flux Calculationsmentioning

confidence: 95%

Development and Testing of Instrumentation for UAV-Based Flux Measurements within Terrestrial and Marine Atmospheric Boundary Layers

Reineman

Lenain

Statom

et al. 2013

Journal of Atmospheric and Oceanic Technology

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“…The VAWR and IMET hourly vector wind speeds showed an −11% difference when both sensors were working, suggesting that the VAWR cup anemometer experienced overspeeding in unsteady conditions (in comparison to the IMET prop and vane sensor). Since earlier comparisons [e.g., Friehe et al , 1984; Beardsley et al , 1997] suggested smaller values or no VAWR cup overspeeding, a value of −6% was used here to estimate the sensitivity of the ST1 surface fluxes to possible cup overspeeding in Table 3. Shipboard observation of the ST1 discus buoy and surface wave height and period measurements made at buoy 44011 both show the ST1 buoy experienced large steep waves during the stronger winter storms.…”

Section: St1 Surface Fluxesmentioning

confidence: 99%

Surface forcing on the southern flank of Georges Bank, February–August 1995

et al. 2003

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[1] Surface wind stress, heat, and freshwater fluxes were estimated over the southern flank of Georges Bank during February-August 1995 using moored measurements made at ST1 located on the 76-m isobath, roughly halfway between the tidal mixing and shelf/ slope fronts. Wind stress variability was dominated by a succession of atmospheric lows that passed Georges Bank during the deployment. A transition between frequent lows and strong wind stress events (''winter'') to less frequent lows and weaker wind stresses (''summer'') occurred in mid-May. In winter, wind stress fluctuations tended to be omnidirectional, with maximum stresses above 0.5 N/m 2 during four storms, one a classic ''nor'easter'', while summer fluctuations were weaker but strongly polarized in the alongbank direction. The ST1 surface heat flux was dominated by shortwave heating, which increased from a winter mean of 130 W/m 2 to 230 W/m 2 in summer. Long-wave cooling decreased from 50 W/m 2 (winter) to 30 W/m 2 (summer), while mean sensible and latent fluxes increased from À20 and À40 W/m 2 (winter) to +10 and 0 (summer) respectively. Overall, winter was characterized by weak net heating (30 W/m 2 ) with shortwave gain offset by long-wave, latent, and sensible heat loss. In summer, increased shortwave gain and reduced long-wave loss and weak sensible and latent fluxes combined to produce strong net heating (210 W/m 2 ). ST1 precipitation was highly episodic with little seasonality while evaporation occurred mostly during winter, resulting in a net evaporation of À15 cm and net freshwater flux of +48 cm over the deployment.

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“…It should be noted that not all of the rms difference between the NSCAT and buoy winds is due to errors in the NSCAT measurements. Buoy winds have been shown to have rms wind speed and direction errors of about 0.8 m s Ϫ1 and 10Њ, respectively (Gilhousen 1987;Beardsley et al 1997;Freilich and Vanhoff 2000, submitted to J. Atmos. Oceanic Technol.).…”

Section: Vector Wind Accuracymentioning

confidence: 99%

Satellite Observations of the Wind Jets off the Pacific Coast of Central America. Part I: Case Studies and Statistical Characteristics

Chelton¹,

Freilich²,

Esbensen³

2000

Mon. Wea. Rev.

159

108

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Measurements of near-surface winds by the NASA scatterometer (NSCAT) from October 1996 through June 1997 are analyzed to investigate the three major wind jets along the Pacific coast of Central America that blow over the Gulfs of Tehuantepec, Papagayo, and Panama. Each jet is easily identifiable as locally intense offshore winds in the lee of low-elevation gaps through the Sierra Madre mountain range. The jets have relatively narrow cross-stream width but often extend several hundred kilometers or more into the Pacific. The Tehuantepec and Papagayo jets sometimes merge with the northeast trade winds of the Pacific. The Tehuantepec jet was highly energetic with characteristic timescales of about 2 days. Events were triggered by high pressures associated with cold surges into the Gulf of Mexico that originated over the Great Plains of North America. The Papagayo and Panama jets were much more persistent than the Tehuantepec jets. The winds at both of these lower-latitude locations exhibited a strong seasonal variation with almost exclusively offshore flow from late November 1996 through late May 1997 and periods of onshore flow in October and November during the late stages of the 1996 Central American monsoon season. Superimposed on this low-frequency seasonal variation were events with characteristic timescales of a few days. Based on NSCAT data, the spatial and temporal evolution of major wind events is described in detail for three representative case studies. In December 1996, the jets developed sequentially from north to south, consistent with the notion that wind events in the two lower-latitude jets are associated with cold-air outbreaks that trigger the Tehuantepec jet a day or so earlier. In November 1996 and March 1997, the Papagayo and Panama jets were strongly influenced by tropical phenomena that had little apparent association with the Tehuantepec jet. These latter two case studies, together with the distinction between the statistical characteristics of the three jets, suggest that the Papagayo and Panama jets are predominantly controlled by a mechanism that is very different from the across-gap pressure gradients associated with high pressure systems of midlatitude origin that control the Tehuantepec jet.

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Intercomparison of Aircraft and Buoy Measurements of Wind and Wind Stress during SMILE*

Cited by 19 publications

References 18 publications

Development and Testing of Instrumentation for UAV-Based Flux Measurements within Terrestrial and Marine Atmospheric Boundary Layers

Development and Testing of Instrumentation for UAV-Based Flux Measurements within Terrestrial and Marine Atmospheric Boundary Layers

Surface forcing on the southern flank of Georges Bank, February–August 1995

Satellite Observations of the Wind Jets off the Pacific Coast of Central America. Part I: Case Studies and Statistical Characteristics

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