Updraft and Downdraft Events in the Atmospheric Boundary Layer Over the Equatorial Pacific Ocean

Greenhut, Gary K.; Khalsa, S. S.

doi:10.1175/1520-0469(1982)039<1803:uadeit>2.0.co;2

Cited by 58 publications

(42 citation statements)

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“…Holt and Raman (1986) showed that the buoyant flux changed to negative above the 50% height of the subcloud layer, but the heat flux changed to negative only above the 30% height of this layer. Greenhut and Khalsa (1982) and Khalsa and Greenhut (1985) showed that updraft regions corresponded to both cool/moist and warm/moist regions in the middle subcloud layer. Nicholls and LeMone (1980) showed that a positive buoyant flux was maintained by the moisture excess in the subcloud layer during the undisturbed period of the GATE.…”

Section: Introductionmentioning

confidence: 97%

Structure of Convective Circulation in the Atmospheric Boundary Layer over the Northwestern Pacific Ocean under a Subtropical High

Shinoda

Higuchi

Tsuboki

et al. 2009

Journal of the Meteorological Society of Japan

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To confirm the structure of convective circulation in the atmospheric boundary layer (ABL) over the northwestern Pacific Ocean around the Southwest Islands of Japan under a subtropical high, we perform intensive observations using radiosonde and Aerosonde in August 2002 and high-resolution three-dimensional numerical simulations. A well-mixed subcloud layer exists below 0.7 km during the observation period. The absolute values of the correlation coe‰cient between anomalies in potential temperature and mixing ratio of water vapor are mainly small (less than 0.3) in the lower subcloud layer. The frequency of a positive correlation coe‰cient at a height of 0.1 km is only 46%. This suggests that fewer warm moist thermals exist in the lower subcloud layer.The simulation results using 100-m horizontal grid resolution show a moist air mass in updraft regions. These thermals are driven by positive buoyant flux, and this positive buoyancy is contributed by moisture, i.e., density anomalies in water vapor and dry air, instead of heat. This should be attributed to the supply of small sensible and abundant latent heat fluxes from the sea surface under the small air-sea temperature di¤erence.

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Section: Introductionmentioning

confidence: 97%

Structure of Convective Circulation in the Atmospheric Boundary Layer over the Northwestern Pacific Ocean under a Subtropical High

Shinoda

Higuchi

Tsuboki

et al. 2009

Journal of the Meteorological Society of Japan

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“…More than 20 years after the pioneering work by Lenschow, Greenhut, Khalsa, and Young, a first comprehensive lidar-based study of updraft and downdraft occurrence frequencies, occurrence durations, corresponding horizontal extents, and mean vertical velocities of updrafts and downdrafts is presented. In contrast to airborne in situ observations (Lenschow and Stephens, 1980;Greenhut and Khalsa, 1982;Khalsa and Greenhut, 1985;Godowitch, 1986;Young, 1988b;Williams and Hacker, 1992;Durand et al, 2000;Said et al, 2009), Doppler lidar allows us to monitor the entire mixed layer including the entrainment zone vertically resolved and continuously over long time periods so that a detailed study of the full evolution cycle of the ABL over the day is possible (Grund et al, 2001;Bösenberg and Linné, 2002;Drobinski et al, 2004;Wulfmeyer and Janjić, 2005;Lothon et al, 2006;Gibert et al, 2007;Engelmann et al, 2008;Hogan et al, 2009).…”

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confidence: 99%

Updraft and downdraft characterization with Doppler lidar: cloud-free versus cumuli-topped mixed layer

2010

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Abstract. For the first time, a comprehensive, heightresolved Doppler lidar study of updrafts and downdrafts in the mixing layer is presented. The Doppler lidar measurements were performed at Leipzig, Germany, in the summer half year of 2006. The conditional sampling method is applied to the measured vertical velocities to identify, count, and analyze significant updraft and downdraft events. Three cases of atmospheric boundary-layer (ABL) evolution with and without fair-weather cumuli formation are discussed. Updrafts occur with an average frequency of 1-2 per unit length z i (boundary-layer depth z i ), downdrafts 20-30% more frequently. In the case with cumuli formation, the draft occurrence frequency is enhanced by about 50% at cloud level or near cloud base. The counted updraft events cover 30-34%, downdrafts 53-57% of the velocity time series in the central part of the ABL (subcloud layer) during the main period of convective activity. By considering all drafts with horizontal extent >36 m in the analysis, the updraft mean horizontal extent ranges here from 200-420 m and is about 0.16 z i -0.18 z i in all three cases disregarding the occurrence of cumulus clouds. Downdraft extents are a factor of 1.3-1.5 larger. The average value of the updraft mean vertical velocities is 0.5-0.7 m/s or 0.40 w * -0.45 w * (convective velocity scale w * ), and the negative downdraft mean vertical velocities are weaker by roughly 10-20%. The analysis of the relationship between the size (horizontal extent) of the updrafts and downdrafts and their mean vertical velocity reveals a pronounced increase of the average vertical velocity in updrafts from 0.4-0.5 m/s for small thermals (100-200 m) to about 1.5 m/s for large updrafts (>600 m) in the subcloud layer in the case with fair-weather cumuli. At cloudless conditions, the updraft velocities were found to be 20% smaller for the large thermals.

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“…The circulations have both ascending and descending branches, and cloudiness can occur (or not) in either branch. Similar ideas have been used in observational studies (based on conditional sampling and/or joint distribution functions) by Stephens ( 1980, 1982 ), Greenhut and Khalsa (1982), and Wilczak and Businger ( 1983 ), Mahrt and Paumier (1984), Grossman (1984), Khalsa and Greenhut (1985), and Penc and Albrecht (1986).…”

Section: Fractional Cloudinessmentioning

confidence: 89%

Cloud parameterization for climate modeling: Status and prospects

Randall

1989

Atmospheric Research

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Updraft and Downdraft Events in the Atmospheric Boundary Layer Over the Equatorial Pacific Ocean

Cited by 58 publications

References 0 publications

Structure of Convective Circulation in the Atmospheric Boundary Layer over the Northwestern Pacific Ocean under a Subtropical High

Structure of Convective Circulation in the Atmospheric Boundary Layer over the Northwestern Pacific Ocean under a Subtropical High

Updraft and downdraft characterization with Doppler lidar: cloud-free versus cumuli-topped mixed layer

Cloud parameterization for climate modeling: Status and prospects

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