Investigating the Summertime Low-Level Jet Over the East Coast of the U.S.A.: A Case Study

Helmis, C. G.; Wang, Q.; Sgouros, G.; Wang, S.; Halios, Christos

doi:10.1007/s10546-013-9841-y

Cited by 20 publications

(32 citation statements)

References 33 publications

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“…The only exception is low‐level jets with cores below 60 m, which occur only during stable conditions and yet would cause the vertical profile to become nonmonotonic. Such low‐level jets are infrequent in Nantucket Sound [ Helmis et al ., ; Mahrt et al ., ] and would explain the few percent cases that are stable or very stable and yet are classified as nonlog in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…Yet there is no published long‐term study on atmospheric stability in the marine boundary layer offshore of the U.S., only two short‐term field campaigns. CBLAST (Coupled Boundary Layers/Air‐Sea Transfer) investigated air‐sea interactions during a few weeks in the summers of 2002 and 2003 using radiosondes, sodar, and a turbulence flux package [ Edson et al ., ; Helmis et al ., , ]. POWER (Position of Offshore Wind Energy Resources) was conducted on a cruise along the coast of New England during July–August 2004 and used a high‐resolution Doppler lidar to measure wind profiles aloft in the wind turbine rotor area [ Pichugina et al ., ].…”

Section: Introductionmentioning

confidence: 99%

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On the predominance of unstable atmospheric conditions in the marine boundary layer offshore of the U.S. northeastern coast

et al. 2016

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The marine boundary layer of the northeastern U.S. is studied with focus on wind speed, atmospheric stability, and turbulent kinetic energy (TKE), the three most relevant properties in the context of offshore wind power development. Two long‐term observational data sets are analyzed. The first one consists of multilevel meteorological variables measured up to 60 m during 2003–2011 at the offshore Cape Wind tower, located near the center of the Nantucket Sound. The second data set comes from the 2013–2014 IMPOWR campaign (Improving the Modeling and Prediction of Offshore Wind Resources), in which wind and wave data were collected with new instruments on the Cape Wind platform, in addition to meteorological data measured during 19 flight missions offshore of New York, Connecticut, Rhode Island, and Massachusetts. It is found that, in this region: (1) the offshore wind resource is remarkable, with monthly average wind speeds at 60 m exceeding 7 m s−1 all year round, highest winds in winter (10.1 m s−1) and lowest in summer (7.1 m s−1), and a distinct diurnal modulation, especially in summer; (2) the marine boundary layer is predominantly unstable (61% unstable vs. 21% neutral vs. 18% stable), meaning that mixing is strong, heat fluxes are positive, and the wind speed profile is often nonlogarithmic (~40% of the time); and (3) the shape of the wind speed profile (log versus nonlog) is an effective qualitative proxy for atmospheric stability, whereas TKE alone is not.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the predominance of unstable atmospheric conditions in the marine boundary layer offshore of the U.S. northeastern coast

et al. 2016

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“…The SODAR measurements were conducted at 30-minute intervals with a vertical resolution of 40 m and a range up to the height of 800 m. The vertical momentum fluxes, the Turbulent Kinetic Energy (TKE) and the turbulence variances for the three wind components were also calculated. More details regarding SODAR system and it parameters can be found at Helmis et al, 2004. Also a laser ceilometer detected the cloud base height continuously.…”

Section: Experimental Area and Instrumentationmentioning

confidence: 99%

On the turbulent structure of the marine atmospheric boundary layer from CBLAST Nantucket measurements

2013

Issue 3

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In this work preliminary results on the characteristics of the turbulent structure of the Marine Atmospheric Boundary Layer (MABL) are presented. Measurements used here were conducted in the framework of the Coupled Boundary Layers Air-Sea Transfer Experiment in Low Wind (CBLAST-Low) project. A number of in situ (fast and slow sensors) and remote sensing (SODAR) instruments were deployed on the coast of Nantucket Island, MA, USA.Measurements of the mean wind, the variances of the three wind components, the atmospheric stability and the momentum fluxes from the acoustic radar (SODAR) revealed the variation of the depth, the turbulent characteristics, and the stability of the MABL in response to the background flow. More specifically, under light south-southwesterly winds, which correspond to the MABL wind directions, the atmosphere was very stable and low values of turbulence were observed. Under moderate to strong southwesterly flow, less stable and neutral atmospheric conditions appeared and the corresponding turbulent quantities were characterized by higher values. The SODAR measurements, with high temporal and spatial resolution, also indicated large magnitude of momentum fluxes at higher levels, presumably associated with the shear forcing near the developed low-level jet.The measurements from the in-situ instrumentation confirmed that the MABL typically has small negative momentum and sensible heat fluxes consistent with stable to neutral stratification while strong diurnal variations were typical for the land surface Atmospheric Boundary Layer (ABL). The developed internal ABL at the experimental site was in general less than 10m during the night and could reach 15m heights during the day, particularly under low-wind conditions.

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“…In the United States, LLJs have been studied most extensively in Great Plains states but also along the northeast and mid‐Atlantic regions of the East Coast. In general, the LLJs of both regions are created by terrain‐induced temperature gradients and then amplified after sunset by the establishment of a stable layer near the surface and the dissipation of surface friction [ Helmis et al ., ]. After sunrise, convective heating of the land will eventually cause the LLJ to decrease in strength [ David , ].…”

Section: Introductionmentioning

confidence: 99%

“…Great Plains LLJs have been described as a response to diurnal heating and cooling of sloping terrain, leading to a periodic variation in thermal wind and a consequent low‐level geostrophic wind oscillation [ Holton , ; Zhang et al ., ]. On the other hand, East Coast LLJs tend to be driven by the differential heating between land and water and are usually found to be part of a larger southwesterly synoptic flow [ Helmis et al ., ; Nunalee and Basu , ].…”

Section: Introductionmentioning

confidence: 99%

Lidar remote sensing of cloud formation caused by low‐level jets

et al. 2016

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In May 2014, the East Hampton Roads Aerosol Flux campaign was conducted at Hampton University to examine small-scale aerosol transport using aerosol, Raman, and Doppler lidars and rawindsonde launches. We present the results of analyses performed on these high-resolution planetary boundary layer and lower atmospheric measurements, with a focus on the low-level jets (LLJs) that form in this region during spring and summer. We present a detailed case study of a LLJ lasting from evening of 20 May to morning of 21 May using vertical profiles of aerosol backscatter, wind speed and direction, water vapor mixing ratio, temperature, and turbulence structure. We show with higher resolution than in previous studies that enhanced nighttime turbulence triggered by LLJs can cause the aerosol and water vapor content of the boundary layer to be transported vertically and form a well-mixed region containing the cloud condensation nuclei that are necessary for cloud formation.Previous studies have documented LLJ characteristics and climatological behavior using observation of rawinsonde [Bonner, 1968;Fast and McCorcle, 1990;Whiteman et al., 1997]. However, the rawinsonde has SU ET AL.CLOUD FORMATION CAUSED BY LOW-LEVEL JETS 5904

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Investigating the Summertime Low-Level Jet Over the East Coast of the U.S.A.: A Case Study

Cited by 20 publications

References 33 publications

On the predominance of unstable atmospheric conditions in the marine boundary layer offshore of the U.S. northeastern coast

On the predominance of unstable atmospheric conditions in the marine boundary layer offshore of the U.S. northeastern coast

On the turbulent structure of the marine atmospheric boundary layer from CBLAST Nantucket measurements

Lidar remote sensing of cloud formation caused by low‐level jets

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