Aircraft and ship observations of the mean structure of the marine boundary layer over the Arabian Sea during MONEX 79

1985 ◽  
Vol 33 (3) ◽  
pp. 259-282 ◽  
Author(s):  
T. Holt ◽  
S. Sethuraman
Keyword(s):  
Boundary Layer ◽  
Arabian Sea ◽  
Marine Boundary Layer ◽  
Mean Structure ◽  
The Mean

scholarly journals Large-Eddy Simulations of a Drizzling, Stratocumulus-Topped Marine Boundary Layer

2009 ◽  
Vol 137 (3) ◽  
pp. 1083-1110 ◽  
Author(s):  
Andrew S. Ackerman ◽  
Margreet C. vanZanten ◽  
Bjorn Stevens ◽  
Verica Savic-Jovcic ◽  
Christopher S. Bretherton ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cloud Water ◽  
Large Eddy Simulations ◽  
Cloud Base ◽  
Entrainment Rate ◽  
Liquid Water Path ◽  
Average Maximum ◽  
Large Eddy ◽  
The Mean

Abstract Cloud water sedimentation and drizzle in a stratocumulus-topped boundary layer are the focus of an intercomparison of large-eddy simulations. The context is an idealized case study of nocturnal stratocumulus under a dry inversion, with embedded pockets of heavily drizzling open cellular convection. Results from 11 groups are used. Two models resolve the size distributions of cloud particles, and the others parameterize cloud water sedimentation and drizzle. For the ensemble of simulations with drizzle and cloud water sedimentation, the mean liquid water path (LWP) is remarkably steady and consistent with the measurements, the mean entrainment rate is at the low end of the measured range, and the ensemble-average maximum vertical wind variance is roughly half that measured. On average, precipitation at the surface and at cloud base is smaller, and the rate of precipitation evaporation greater, than measured. Including drizzle in the simulations reduces convective intensity, increases boundary layer stratification, and decreases LWP for nearly all models. Including cloud water sedimentation substantially decreases entrainment, decreases convective intensity, and increases LWP for most models. In nearly all cases, LWP responds more strongly to cloud water sedimentation than to drizzle. The omission of cloud water sedimentation in simulations is strongly discouraged, regardless of whether or not precipitation is present below cloud base.

Elevated Levels of Biogenic Nonmethane Hydrocarbons in the Marine Boundary Layer of the Arabian Sea During the Intermonsoon

2020 ◽  
Vol 125 (22) ◽  
Author(s):  
Nidhi Tripathi ◽  
L. K. Sahu ◽  
Arvind Singh ◽  
Ravi Yadav ◽  
Anil Patel ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Arabian Sea ◽  
Marine Boundary Layer ◽  
Nonmethane Hydrocarbons

scholarly journals Missing OH reactivity in the global marine boundary layer

2020 ◽  
Vol 20 (6) ◽  
pp. 4013-4029 ◽  
Author(s):  
Alexander B. Thames ◽  
William H. Brune ◽  
David O. Miller ◽  
Hannah M. Allen ◽  
Eric C. Apel ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Dimethyl Sulfide ◽  
Marine Boundary Layer ◽  
Limit Of Detection ◽  
Chemical Species ◽  
Volatile Organic ◽  
The Mean ◽  
The Difference

Abstract. The hydroxyl radical (OH) reacts with thousands of chemical species in the atmosphere, initiating their removal and the chemical reaction sequences that produce ozone, secondary aerosols, and gas-phase acids. OH reactivity, which is the inverse of OH lifetime, influences the OH abundance and the ability of OH to cleanse the atmosphere. The NASA Atmospheric Tomography (ATom) campaign used instruments on the NASA DC-8 aircraft to measure OH reactivity and more than 100 trace chemical species. ATom presented a unique opportunity to test the completeness of the OH reactivity calculated from the chemical species measurements by comparing it to the measured OH reactivity over two oceans across four seasons. Although the calculated OH reactivity was below the limit of detection for the ATom instrument used to measure OH reactivity throughout much of the free troposphere, the instrument was able to measure the OH reactivity in and just above the marine boundary layer. The mean measured value of OH reactivity in the marine boundary layer across all latitudes and all ATom deployments was 1.9 s−1, which is 0.5 s−1 larger than the mean calculated OH reactivity. The missing OH reactivity, the difference between the measured and calculated OH reactivity, varied between 0 and 3.5 s−1, with the highest values over the Northern Hemisphere Pacific Ocean. Correlations of missing OH reactivity with formaldehyde, dimethyl sulfide, butanal, and sea surface temperature suggest the presence of unmeasured or unknown volatile organic compounds or oxygenated volatile organic compounds associated with ocean emissions.

Response of a turbulent boundary layer to sinusoidal free-stream unsteadiness

1990 ◽  
Vol 221 ◽  
pp. 131-159 ◽  
Author(s):  
G. J. Brereton ◽  
W. C. Reynolds ◽  
R. Jayaraman
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Steady Flow ◽  
Boundary Layers ◽  
Free Stream ◽  
Constant Pressure ◽  
External Conditions ◽  
Mean Structure ◽  
The Mean ◽  
Turbulence Production

In this paper, selected findings of a detailed experimental investigation are reported concerning the effects of forced free-stream unsteadiness on a turbulent boundary layer. The forced unsteadiness was sinusoidal and was superimposed locally on an otherwise-steady mainstream, beyond a turbulent boundary layer which had developed under constant-pressure conditions. Within the region over which free-stream unsteadiness was induced, the sinusoidal variation in pressure gradient was between extremes of zero and a positive value, with a positive average level. The local response of the boundary layer to these free-stream effects was studied through simultaneous measurements of the u- and v-components of the velocity fieldAlthough extensive studies of unsteady, turbulent, fully-developed pipe and channel flow have been carried out, the problem of a developing turbulent boundary layer and its response to forced free-stream unsteadiness has received comparatively little attention. The present study is intended to redress this imbalance and, when contrasted with other studies of unsteady turbulent boundary layers, is unique in that: (i) it features an appreciable amplitude of mainstream modulation at a large number of frequencies of forced unsteadiness, (ii) its measurements are both detailed and of high spatial resolution, so that the near-wall behaviour of the flow can be discerned, and (iii) it allows local modulation of the mainstream beyond a turbulent boundary layer which has developed under the well-known conditions of steady, two-dimensional, constant-pressure flowResults are reported which allow comparison of the behaviour of boundary layers under the same mean external conditions, but with different time dependence in their free-stream velocities. These time dependences correspond to: (i) steady flow, (ii) quasi-steadily varying flow, and (iii) unsteady flow at different frequencies of mainstream unsteadiness. Experimental results focus upon the time-averaged nature of the flow; they indicate that the mean structure of the turbulent boundary layer is sufficiently robust that the imposition of free-stream unsteadiness results only in minor differences relative to the mean character of the steady flow, even at frequencies for which the momentary condition of the flow departs substantially from its quasi-steady state. Mean levels of turbulence production are likewise unaffected by free-stream unsteadiness and temporal production of turbulence appears to result only from modulation of the motions which contribute to turbulence production as a time-averaged measure.

scholarly journals Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign

2013 ◽  
Vol 13 (1) ◽  
pp. 1489-1526 ◽  
Author(s):  
D. Jarecka ◽  
H. Pawlowska ◽  
W. W. Grabowski ◽  
A. A. Wyszogrodzki
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Marine Boundary Layer ◽  
Subgrid Scale ◽  
Field Campaign ◽  
Eddy Simulation ◽  
Warm Rain ◽  
Large Eddy ◽  
Double Moment ◽  
The Mean

Abstract. This paper discusses aircraft observations and large-eddy simulation (LES) of the 15 May 2008, North Sea boundary-layer clouds from the EUCAARI-IMPACT field campaign. These clouds were advected from the north-east by the prevailing lower-tropspheric winds, and featured stratocumulus-over-cumulus cloud formations. Almost-solid stratocumulus deck in the upper part of the relatively deep weakly decoupled marine boundary layer overlaid a field of small cumuli with a cloud fraction of ~10%. The two cloud formations featured distinct microphysical characteristics that were in general agreement with numerous past observations of strongly-diluted shallow cumuli on the one hand and solid marine boundary-layer stratocumulus on the other. Macrophysical and microphysical cloud properties were reproduced well by the double-moment warm-rain microphysics large-eddy simulation. A novel feature of the model is its capability to locally predict homogeneity of the subgrid-scale mixing between the cloud and its cloud-free environment. In the double-moment warm-rain microphysics scheme, the homogeneity is controlled by a single parameter α, that ranges from 0 to 1 and limiting values representing the homogeneous and the extremely inhomogeneous mixing scenarios, respectively. Parameter α depends on the characteristic time scales of the droplet evaporation and of the turbulent homogenization. In the model, these scales are derived locally based on the subgrid-scale turbulent kinetic energy, spatial scale of cloudy filaments, the mean cloud droplet radius, and the humidity of the cloud-free air entrained into the cloud. Simulated mixing is on average quite inhomogeneous, with the mean parameter α around 0.7 across the entire depth of the cloud field, but with local variations across almost the entire range, especially near the base and the top of the cloud field.

scholarly journals On the transitions in marine boundary layer cloudiness

2010 ◽  
Vol 10 (5) ◽  
pp. 2377-2391 ◽  
Author(s):  
I. Sandu ◽  
B. Stevens ◽  
R. Pincus
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Data Sets ◽  
Lagrangian Analysis ◽  
Air Masses ◽  
Upper Tropospheric Humidity ◽  
The Mean ◽  
Subtropical Oceans ◽  
Cloud Evolution

Abstract. Satellite observations and meteorological reanalysis are used to examine the transition from unbroken sheets of stratocumulus to fields of scattered cumulus, and the processes controlling them, in four subtropical oceans. A Lagrangian analysis suggests that both the transition, defined as the temporal evolution in cloudiness, and the processes driving the transition, are quite similar among the subtropical oceans. The increase in sea surface temperature and the associated decrease in lower tropospheric stability appear to play a far more important role in cloud evolution than other factors including changes in large scale divergence and upper tropospheric humidity. During the summer months, the transitions in marine boundary layer cloudiness appear so systematically that their characteristics obtained by documenting the flow of thousands of individual air masses are well reproduced by the mean (or climatological) fields of the different data sets. This highlights interesting opportunities for future observational and modeling studies of these transitions.

High Levels of Isoprene in the Marine Boundary Layer of the Arabian Sea during Spring Inter-Monsoon: Role of Phytoplankton Blooms

2020 ◽  
Vol 4 (4) ◽  
pp. 583-590 ◽  
Author(s):  
Nidhi Tripathi ◽  
L. K. Sahu ◽  
Arvind Singh ◽  
Ravi Yadav ◽  
Kusum Komal Karati
Keyword(s):  
Boundary Layer ◽  
Arabian Sea ◽  
Marine Boundary Layer ◽  
Phytoplankton Blooms
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