Regional flow conditions associated with stratocumulus cloud-eroding boundaries over the southeast Atlantic

2021 ◽  
Author(s):  
Laura M. Tomkins ◽  
David B. Mechem ◽  
Sandra E. Yuter ◽  
Spencer R. Rhodes
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Weather Research And Forecasting ◽  
Marine Stratocumulus ◽  
Boundary Layer Height ◽  
Regional Flow ◽  
Stratocumulus Clouds ◽  
Offshore Flow ◽  
Passive Tracers ◽  
Atmospheric Gravity

AbstractLarge, abrupt clearing events have been documented in the marine stratocumulus cloud deck over the subtropical Southeast Atlantic Ocean. In these events, clouds are rapidly eroded along a line hundreds–to–thousands of kilometers in length that generally moves westward away from the coast. Because marine stratocumulus clouds exert a strong cooling effect on the planet, any phenomenon that acts to erode large areas of low clouds may be climatically important. Previous satellite-based research suggests that the cloud-eroding boundaries may be caused by westward-propagating atmospheric gravity waves rather than simple advection of the cloud. The behavior of the coastal offshore flow, which is proposed as a fundamental physical mechanism associated with the clearing events, is explored using the Weather Research and Forecasting model. Results are presented from several week-long simulations in the month of May when cloud-eroding boundaries exhibit maximum frequency. Two simulations cover periods containing multiple cloud-eroding boundaries (active periods), and two other simulations cover periods without any cloud-eroding boundaries (null periods). Passive tracers and an analysis of mass flux are used to assess the character of the diurnal west-African coastal circulation. Results indicate that the active periods containing cloud-eroding boundaries regularly experience stronger and deeper nocturnal offshore flow from the continent above the marine boundary layer, compared to the null periods. Additionally, we find that the boundary layer height is higher in the null periods than in the active periods, suggesting that the active periods are associated with areas of thinner clouds that may be more susceptible to cloud erosion.

Can Marine Cloud Brightening Reduce Sea-Surface Temperatures to Moderate Extreme Hurricanes and Typhoons?

2021 ◽  
Vol 6 (3) ◽  
Author(s):  
Salter SH ◽  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Sea Water ◽  
Cloud Condensation Nuclei ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Marine Stratocumulus ◽  
Surface Temperatures ◽  
Stratocumulus Clouds ◽  
Cloud Tops

Elevated sea-surface temperatures are a necessary but not sufficient requirement for the formation of hurricanes and typhoons. This paper suggests a way to exploit this. Twomey [1] showed that cloud reflectivity depends on the size-distribution of cloud drops, with a large number of small drops reflecting more than a smaller number of larger ones. Mid-ocean air is cleaner than over land. Latham [2-4] suggested that reflectivity of marine stratocumulus clouds could be increased by releasing a submicron spray of filtered sea water into the bottom of the marine boundary layer. The salt residues left after evaporation would be mixed by turbulence through the full depth of the marine boundary layer and would be ideal cloud condensation nuclei. Those that reached a height where the air had a super-saturation above 100% by enough to get over the peak of the Köhler curve would produce an increased number of cloud drops and so trigger the Twomey effect. The increase in reflection from cloud tops back out to space would cool sea-surface water. We are not trying to increase cloud cover; we just want to make existing cloud tops whiter. The spray could be produced by wind-driven vessels cruising chosen ocean regions. The engineering design of sea-going hardware is well advanced. This paper suggests a way to calculate spray quantities and the number and cost of spray vessels to achieve a hurricane reduction to a more acceptable intensity. It is intended to show the shape of a possible calculation with credible if not exact assumptions. Anyone with better assumptions should be able to follow the process.

scholarly journals Cloud Processing of Aerosol Particles in Marine Stratocumulus Clouds

Atmosphere ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 520 ◽  
Author(s):  
Andrea I. Flossmann ◽  
Wolfram Wobrock
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Numerical Study ◽  
Spatial Scales ◽  
Aerosol Particles ◽  
Cloud Microphysics ◽  
Marine Stratocumulus ◽  
Boundary Layer Clouds ◽  
Cloud Processing ◽  
Stratocumulus Clouds

Cloud processing of aerosol particles is an important process and is, for example, thought to be responsible for the so-called “Hoppel-minimum” in the marine aerosol particle distribution or contribute to the cell organization of marine boundary layer clouds. A numerical study of the temporal and spatial scales of the processing of aerosol particles by typical marine stratocumulus clouds is presented. The dynamical framework is inspired by observations during the VOCALS (Variability of the American Monsoon System Ocean-Cloud-Atmosphere-Land Study) Regional Experiment in the Southeast Pacific. The 3-D mesoscale model version of DESCAM (Detailed Scavenging Model) follows cloud microphysics of the stratocumulus deck in a bin-resolved manner and has been extended to keep track of cloud-processed particles in addition to non-processed aerosol particles in the air and inside the cloud drops. The simulation follows the evolution of the processing of aerosol particles by the cloud. It is found that within one hour almost all boundary layer aerosol particles have passed through at least one cloud cycle. However, as the in-cloud residence times of the particles in the considered case are only on the order of minutes, the aerosol particles remain essentially unchanged. Our findings suggest that in order to produce noticeable microphysical and dynamical effects in the marine boundary layer clouds, cloud processing needs to continue for extended periods of time, exceeding largely the time period considered in the present study. A second model study is dedicated to the interaction of ship track particles with marine boundary layer clouds. The model simulates quite satisfactorily the incorporation of the ship plume particles into the cloud. The observed time and spatial scales and a possible Twomey effect were reproduced.

scholarly journals Turbulence in The Marine Boundary Layer and Air Motions Below Stratocumulus Clouds at the ARM Eastern North Atlantic Site

2021 ◽  
Author(s):  
Virendra P. Ghate ◽  
Maria P. Cadeddu ◽  
Xue Zheng ◽  
Ewan O’Connor
Keyword(s):  
Boundary Layer ◽  
North Atlantic ◽  
Vertical Velocity ◽  
Marine Boundary Layer ◽  
Cloud Layer ◽  
Similar Amount ◽  
Marine Stratocumulus ◽  
Stratocumulus Clouds ◽  
Eastern North Atlantic ◽  
Rain Rates

AbstractMarine stratocumulus clouds are intimately coupled to the turbulence in the boundary layer and drizzle is known to be ubiquitous within them. Six years of data collected at the Atmospheric Radiation Measurement (ARM)’s Eastern North Atlantic site are utilized to characterize turbulence in the marine boundary layer and air motions below stratocumulus clouds. Profiles of variance of vertical velocity binned by wind direction (wdir) yielded that the boundary layer measurements are affected by the island when the wdir is between 90° and 310° (measured clockwise from North where air is coming from). Data collected during the marine conditions (wdir<90 or wdir>310) showed that the variance of vertical velocity was higher during the winter months than during the summer months due to higher cloudiness, wind speeds, and surface fluxes. During marine conditions the variance of vertical velocity and cloud fraction exhibited a distinct diurnal cycle with higher values during the nighttime than during the daytime. Detailed analysis of 32 cases of drizzling marine stratocumulus clouds showed that for a similar amount of radiative cooling at the cloud top, within the sub-cloud layer 1) drizzle increasingly falls within downdrafts with increasing rain rates, 2) the strength of the downdrafts increases with increasing rain rates, and 3) the correlation between vertical air motion and rain rate is highest in the middle of the sub-cloud layer. The results presented herein have implications for climatological and model evaluation studies conducted at the ENA site, along with efforts of accurately representing drizzle-turbulence interactions in a range of atmospheric models.

An Unusual Aerial Photograph of an Eddy Circulation in Marine Stratocumulus Clouds

2015 ◽  
Vol 143 (2) ◽  
pp. 419-432 ◽  
Author(s):  
Bradley M. Muller ◽  
Christopher G. Herbster ◽  
Frederick R. Mosher
Keyword(s):  
Boundary Layer ◽  
Aerial Photograph ◽  
Marine Boundary Layer ◽  
Model Simulation ◽  
Surface Wind ◽  
Formation Mechanisms ◽  
Marine Stratocumulus ◽  
Surface Evolution ◽  
Strong Inversion ◽  
Stratocumulus Clouds

Abstract An aerial photograph of a cyclonic, von Kármán–like vortex in the marine stratocumulus clouds off the California coast, taken by a commercial pilot near Grover Beach, is presented. It is believed that this is the first photograph of such an eddy, taken from an airplane, to appear in publication. The eddy occurred with a strong inversion above a shallow marine boundary layer, in the lee of high, inversion-penetrating terrain. Tower and surface wind measurements plotted on satellite imagery demonstrate that the Grover Beach eddy was not just a cloud-level feature, but extended through the marine atmospheric boundary layer (MABL) to the surface. Evolution of the flow during the formation of the eddy appears similar to idealized numerical simulations of blocked MABL flow from the literature. The tower measurements sampled the northern part of the eddy circulation during its formation just offshore. The 2°–3°C temperature increases and then decreases during and after the eddy passage may be indicative of warmer air, from sheltered locations to the southeast, and/or downslope flow, being advected by and included into the eddy circulation. Satellite data compared with sequences of wind reversals at two different levels of the meteorological tower suggest that the eddy is tilted with height, at least during its formation stage. Formation mechanisms are discussed, but the subsynoptic observations are inadequate to resolve basic questions about the flow; ultimately a high-resolution model simulation is needed.

scholarly journals Effect of biomass burning on marine stratocumulus clouds off the California coast

2009 ◽  
Vol 9 (22) ◽  
pp. 8841-8856 ◽  
Author(s):  
J. Brioude ◽  
O. R. Cooper ◽  
G. Feingold ◽  
M. Trainer ◽  
S. R. Freitas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Cloud Fraction ◽  
Marine Stratocumulus ◽  
Cloud Albedo ◽  
Stratocumulus Clouds ◽  
Absorbing Aerosols ◽  
Indirect Radiative Forcing

Abstract. Aerosol-cloud interactions are considered to be one of the most important and least known forcings in the climate system. Biomass burning aerosols are of special interest due to their radiative impact (direct and indirect effect) and their potential to increase in the future due to climate change. Combining data from Geostationary Operational Environmental Satellite (GOES) and MODerate-resolution Imaging Spectroradiometer (MODIS) with passive tracers from the FLEXPART Lagrangian Particle Dispersion Model, the impact of biomass burning aerosols on marine stratocumulus clouds has been examined in June and July of 2006–2008 off the California coast. Using a continental tracer, the indirect effect of biomass burning aerosols has been isolated by comparing the average cloud fraction and cloud albedo for different meteorological situations, and for clean versus polluted (in terms of biomass burning) continental air masses at 14:00 local time. Within a 500 km-wide band along the coast of California, biomass burning aerosols, which tend to reside above the marine boundary layer, increased the cloud fraction by 0.143, and the cloud albedo by 0.038. Absorbing aerosols located above the marine boundary layer lead to an increase of the lower tropospheric stability and a reduction in the vertical entrainment of dry air from above, leading to increased cloud formation. The combined effect was an indirect radiative forcing of −7.5% ±1.7% (cooling effect) of the outgoing radiative flux at the top of the atmosphere on average, with a bias due to meteorology of +0.9%. Further away from the coast, the biomass burning aerosols, which were located within the boundary layer, reduced the cloud fraction by 0.023 and the cloud albedo by 0.006, resulting in an indirect radiative forcing of +1.3% ±0.3% (warming effect) with a bias of +0.5%. These results underscore the dual role that absorbing aerosols play in cloud radiative forcing.

scholarly journals Lidar-based remote sensing of atmospheric boundary layer height over land and ocean

2014 ◽  
Vol 7 (1) ◽  
pp. 173-182 ◽  
Author(s):  
T. Luo ◽  
R. Yuan ◽  
Z. Wang
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Marine Boundary Layer ◽  
Mixing Layer ◽  
Layer Height ◽  
Boundary Layer Height ◽  
Lidar Measurements ◽  
Mixing Layer Height ◽  
Atmospheric Radiation Measurement ◽  
Atmospheric Boundary Layer Height

Abstract. Atmospheric boundary layer (ABL) processes are important in climate, weather and air quality. A better understanding of the structure and the behavior of the ABL is required for understanding and modeling of the chemistry and dynamics of the atmosphere on all scales. Based on the systematic variations of the ABL structures over different surfaces, different lidar-based methods were developed and evaluated to determine the boundary layer height and mixing layer height over land and ocean. With Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) micropulse lidar (MPL) and radiosonde measurements, diurnal and season cycles of atmospheric boundary layer depth and the ABL vertical structure over ocean and land are analyzed. The new methods are then applied to satellite lidar measurements. The aerosol-derived global marine boundary layer heights are evaluated with marine ABL stratiform cloud top heights and results show a good agreement between them.

scholarly journals Wind speed response of marine non-precipitating stratocumulus clouds over a diurnal cycle in cloud-system resolving simulations

2016 ◽  
Vol 16 (9) ◽  
pp. 5811-5839 ◽  
Author(s):  
Jan Kazil ◽  
Graham Feingold ◽  
Takanobu Yamaguchi
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Large Scale ◽  
Layer Growth ◽  
Radiative Properties ◽  
Cloud Base ◽  
Latent Heat Release ◽  
Marine Stratocumulus ◽  
Stratocumulus Clouds ◽  
Boundary Layer Growth

Abstract. Observed and projected trends in large-scale wind speed over the oceans prompt the question: how do marine stratocumulus clouds and their radiative properties respond to changes in large-scale wind speed? Wind speed drives the surface fluxes of sensible heat, moisture, and momentum and thereby acts on cloud liquid water path (LWP) and cloud radiative properties. We present an investigation of the dynamical response of non-precipitating, overcast marine stratocumulus clouds to different wind speeds over the course of a diurnal cycle, all else equal. In cloud-system resolving simulations, we find that higher wind speed leads to faster boundary layer growth and stronger entrainment. The dynamical driver is enhanced buoyant production of turbulence kinetic energy (TKE) from latent heat release in cloud updrafts. LWP is enhanced during the night and in the morning at higher wind speed, and more strongly suppressed later in the day. Wind speed hence accentuates the diurnal LWP cycle by expanding the morning–afternoon contrast. The higher LWP at higher wind speed does not, however, enhance cloud top cooling because in clouds with LWP ⪆ 50 g m−2, longwave emissions are insensitive to LWP. This leads to the general conclusion that in sufficiently thick stratocumulus clouds, additional boundary layer growth and entrainment due to a boundary layer moistening arises by stronger production of TKE from latent heat release in cloud updrafts, rather than from enhanced longwave cooling. We find that large-scale wind modulates boundary layer decoupling. At nighttime and at low wind speed during daytime, it enhances decoupling in part by faster boundary layer growth and stronger entrainment and in part because shear from large-scale wind in the sub-cloud layer hinders vertical moisture transport between the surface and cloud base. With increasing wind speed, however, in decoupled daytime conditions, shear-driven circulation due to large-scale wind takes over from buoyancy-driven circulation in transporting moisture from the surface to cloud base and thereby reduces decoupling and helps maintain LWP. The total (shortwave + longwave) cloud radiative effect (CRE) responds to changes in LWP and cloud fraction, and higher wind speed translates to a stronger diurnally averaged total CRE. However, the sensitivity of the diurnally averaged total CRE to wind speed decreases with increasing wind speed.

Observations of the Interaction between Cumulus Clouds and Warm Stratocumulus Clouds in the Marine Boundary Layer during ASTEX

1995 ◽  
Vol 52 (16) ◽  
pp. 2902-2922 ◽  
Author(s):  
G. M. Martin ◽  
D. W. Johnson ◽  
D. P. Rogers ◽  
P. R. Jonas ◽  
P. Minnis ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cumulus Clouds ◽  
Stratocumulus Clouds

scholarly journals Precipitation susceptibility in marine stratocumulus and shallow cumulus from airborne measurements

2016 ◽  
Vol 16 (17) ◽  
pp. 11395-11413 ◽  
Author(s):  
Eunsil Jung ◽  
Bruce A. Albrecht ◽  
Armin Sorooshian ◽  
Paquita Zuidema ◽  
Haflidi H. Jonsson
Keyword(s):  
Marine Boundary Layer ◽  
Qualitative Behavior ◽  
Liquid Water Path ◽  
Cumulus Clouds ◽  
Marine Stratocumulus ◽  
Airborne Measurements ◽  
Boundary Layer Clouds ◽  
Shallow Cumulus ◽  
Stratocumulus Clouds ◽  
Field Campaigns

Abstract. Precipitation tends to decrease as aerosol concentration increases in warm marine boundary layer clouds at fixed liquid water path (LWP). The quantitative nature of this relationship is captured using the precipitation susceptibility (So) metric. Previously published works disagree on the qualitative behavior of So in marine low clouds: So decreases monotonically with increasing LWP or cloud depth (H) in stratocumulus clouds (Sc), while it increases and then decreases in shallow cumulus clouds (Cu). This study uses airborne measurements from four field campaigns on Cu and Sc with similar instrument packages and flight maneuvers to examine if and why So behavior varies as a function of cloud type. The findings show that So increases with H and then decreases in both Sc and Cu. Possible reasons for why these results differ from those in previous studies of Sc are discussed.

scholarly journals Lidar-based remote sensing of atmospheric boundary layer height over land and ocean

2013 ◽  
Vol 6 (5) ◽  
pp. 8311-8338
Author(s):  
T. Luo ◽  
R. Yuan ◽  
Z. Wang
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Marine Boundary Layer ◽  
Layer Structure ◽  
Mixing Layer ◽  
Layer Height ◽  
Boundary Layer Height ◽  
Lidar Measurements ◽  
Mixing Layer Height ◽  
Atmospheric Radiation Measurement

Abstract. Atmospheric boundary layer (ABL) processes are important in climate, weather and air quality. A better understanding of the structure and the behavior of the ABL is required for understanding and modeling of the chemistry and dynamics of the atmosphere on all scales. Based on the systematic variations of ABL structures over different surfaces, different lidar-based methods were developed and evaluated to determine the boundary layer height and mixing layer height over land and ocean. With Atmospheric Radiation Measurement Program (ARM) Climate Research Facility (ACRF) micropulse lidar (MPL) and radiosonde measurements, diurnal and season cycles of atmospheric boundary layer depth and ABL vertical structure over ocean (TWP_C2 cite) and land (SGP_C1) are analyzed. The new methods are also applied to satellite lidar measurements. The derived global marine boundary layer structure database shows good agreement with marine ABL stratiform cloud top height.

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