An observation of sea‐spray microphysics by airborne Doppler radar

Fairall, C. W.; Pezoa, Sergio; Moran, K. P.; Wolfe, Dan

doi:10.1002/2014gl060062

Cited by 9 publications

(8 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Sea‐spray spume droplet mass concentration for different wind speeds at 100 m. The square is from Fairall et al [] for 15 m s −1 < U 10 < 20 m s −1 ; the diamond is the mean results from the Cloud Imaging Probe (CIP) for U 10 ≥ 23 m s −1 (the average height is 150 m); and the triangle is from the numerical model study of Shpund et al [] for U 10 = 25 m s −1 .…”

Section: Resultsmentioning

confidence: 99%

“…(1) The lack of knowledge of the air‐sea boundary in high winds, as the near‐surface experimental observations of aerosols and turbulence in high winds, especially in extreme conditions, are challenging [ Fairall et al , ], and the structure and characteristics of the high‐wind ABL over the ocean are less known. Ships and research aircraft prefer to avoid such conditions, while fixed platforms offer rare sampling opportunities and may disturb the observations [ Fairall et al , ]. (2) There are unclear interactions between spume droplets and the high‐wind ABL.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

On the upward flux of sea‐spray spume droplets in high‐wind conditions

Cheng

Qingcun

et al. 2017

JGR Atmospheres

View full text Add to dashboard Cite

It has been speculated that the spume droplets torn off from ocean waves in high wind speeds (larger than about 9 m s−1) enhance air‐sea fluxes. However, the vertical transport of spume droplets in the high‐wind atmospheric boundary layer (ABL) is little researched and lacks the support of numerical simulations. Based on observational data and the characteristics of high‐wind ABL above the ocean, the vertical transport of spume droplets is studied and simulated. It is revealed that the existence of gusty wind with coherent structure during high winds is favorable for the vertical transport of the large‐size droplets. The trajectories of 1000 spume droplets with different sizes under different wind speeds in the range 10–35 m s−1 are calculated, and the uplifting fraction of spume droplets that can reach the 100 m height in the ABL is parameterized by using a nondimensional factor U102/(r80g), where U10 is the wind speed at 10 m height, r80 the equilibrium radius of droplet at an equivalent 80% relative humidity, and g the gravitational acceleration. Then, the upward flux of large‐size spume droplets and the mass concentration at 100 m height are evaluated. These numerical results are comparable to some observational data and show that the large‐size spume droplets can be entrained into the ABL during high winds and then contribute to the air‐sea mass fluxes.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the upward flux of sea‐spray spume droplets in high‐wind conditions

Cheng

Qingcun

et al. 2017

JGR Atmospheres

View full text Add to dashboard Cite

show abstract

“…A microwave radiometer provided LWP estimates every 10 min (Zuidema et al, 2005;de Szoeke et al, 2012). The 94 GHz (W-band) cloud radar produced data at the same time frequency (Moran et al, 2011;de Szoeke et al, 2012;Fairall et al, 2014) and is used to evaluate model drizzle and large droplet properties. the cloud optical depth (τ ) is estimated by assuming that the clouds are adiabatic (or some constant fraction of adiabatic) so that their liquid water increases linearly with height, and it is assumed that N d is constant throughout their depth.…”

Section: Discussionmentioning

confidence: 99%

“…POCs constitute regions of open cells with low cloud fraction in amongst high-cloud-fraction closedcell regions (Wood et al, 2011a). It has been suggested that the enhancement of precipitation by reduced aerosol concentrations can cause a transition between a state of closed and open cells within stratocumulus (Rosenfeld et al, 2006), which is then enhanced by a positive feedback mechanism that has been called the "runaway precipitation sink" (Feingold and Kreidenweis, 2002), whereby precipitation leads to a reduction in the available CCN. All else being equal, reducing CCN leads to larger drops that enhance the formation of precipitation, promoting the removal of more CCN.…”

Section: Introductionmentioning

confidence: 99%

The relative importance of macrophysical and cloud albedo changes for aerosol-induced radiative effects in closed-cell stratocumulus: insight from the modelling of a case study

et al. 2017

View full text Add to dashboard Cite

Abstract. Aerosol-cloud interactions are explored using 1 km simulations of a case study of predominantly closedcell SE Pacific stratocumulus clouds. The simulations include realistic meteorology along with newly implemented cloud microphysics and sub-grid cloud schemes. The model was critically assessed against observations of liquid water path (LWP), broadband fluxes, cloud fraction (f c ), droplet number concentrations (N d ), thermodynamic profiles, and radar reflectivities.Aerosol loading sensitivity tests showed that at low aerosol loadings, changes to aerosol affected shortwave fluxes equally through changes to cloud macrophysical characteristics (LWP, f c ) and cloud albedo changes due solely to N d changes. However, at high aerosol loadings, only the N d albedo change was important. Evidence was also provided to show that a treatment of sub-grid clouds is as important as order of magnitude changes in aerosol loading for the accurate simulation of stratocumulus at this grid resolution.Overall, the control model demonstrated a credible ability to reproduce observations, suggesting that many of the important physical processes for accurately simulating these clouds are represented within the model and giving some confidence in the predictions of the model concerning stratocumulus and the impact of aerosol. For example, the control run was able to reproduce the shape and magnitude of the observed diurnal cycle of domain mean LWP to within ∼ 10 g m −2 for the nighttime, but with an overestimate for the daytime of up to 30 g m −2 . The latter was attributed to the uniform aerosol fields imposed on the model, which meant that the model failed to include the low-N d mode that was observed further offshore, preventing the LWP removal through precipitation that likely occurred in reality. The boundary layer was too low by around 260 m, which was attributed to the driving global model analysis. The shapes and sizes of the observed bands of clouds and open-cell-like regions of low areal cloud cover were qualitatively captured. The daytime f c frequency distribution was reproduced to within f c = 0.04 for f c >∼ 0.7 as was the domain mean nighttime f c (at a single time) to within f c = 0.02. Frequency distributions of shortwave top-of-the-atmosphere (TOA) fluxes from the satellite were well represented by the model, with only a slight underestimate of the mean by 15 %; this was attributed to near-shore aerosol concentrations that were too low for the particular times of the satellite overpasses. TOA long-wave flux distributions were close to those from the satellite with agreement of the mean value to within 0.4 %. From comparisons of N d distributions to those from the satellite, it was found that the N d mode from the model agreed with the higher of the two observed modes to within ∼ 15 %.

show abstract

“…A microwave radiometer provided LWP estimates every 10 minutes (Zuidema et al, 2005;de Szoeke et al, 2012). The 94 GHz (W-band) cloud radar produced data at the same time frequency (Moran et al, 2011;de Szoeke et al, 2012;Fairall et al, 2014) and is used to evaluate model drizzle and large droplet properties.…”

mentioning

confidence: 99%

The relative importance of macrophysical and cloud albedo changes for aerosol induced radiative effects in stratocumulus

Grosvenor

Field

Hill

et al. 2016

Preprint

View full text Add to dashboard Cite

Abstract. Aerosol-cloud interactions are explored using 1&#8201;km resolution simulations of SE Pacific stratocumulus clouds that include realistic meteorology along with newly implemented cloud microphysics and sub-grid cloud schemes. The model was critically assessed against observations of Liquid Water Path (LWP), broadband fluxes, cloud fraction (fc), droplet number concentrations (Nd) and radar reflectivities. Aerosol loading sensitivity tests showed that at low aerosol loadings, changes to aerosol affected shortwave fluxes equally through changes to cloud macrophysical charateristics (LWP, fc) and cloud albedo changes due solely to Nd changes. However, at high aerosol loadings, only the Nd albedo change was important. Evidence was also provided to show that a treatment of sub-grid clouds is as important as order of magnitude changes in aerosol loading for the accurate simulation of stratocumulus at this grid resolution. Overall, the control model demonstrated a credible ability to reproduce observations suggesting that many of the important physical processes for accurately simulating these clouds are represented within the model and giving some confidence in the predictions of the model concerning stratocumulus and the impact of aerosol. For example, the control run was able to reproduce the shape and magnitude of the observed diurnal cycle of domain mean LWP to within ~&#8201;10&#8201;g&#8201;m&#8722;2 for the nighttime, but with an overestimate for the daytime of up to 30&#8201;g&#8201;m&#8722;2. The latter was attributed to the uniform aerosol fields imposed on the model, which meant that the model failed to include the low Nd mode that was observed further offshore, preventing the LWP removal through precipitation that likely occurred in reality. The boundary layer was too low by around 260&#8201;m, which was attributed to the driving global model analysis. The shapes and sizes of the observed bands of clouds and open-cell-like regions of low areal cloud cover were qualitatively captured. The daytime fc frequency distribution was reproduced to within fc&#8201;=&#8201;0.04 for fc&#8201;>&#8201;~&#8201;0.7 as was the domain mean nighttime fc (at a single time) to within fc&#8201;=&#8201;0.02. Frequency distributions of shortwave top-of-the-atmosphere (TOA) fluxes from satellite were well represented by the model with only a slight underestimate of the mean by 15&#8201;%; this was attributed to near--shore aerosol concentrations that were too low for the particular times of the satellite overpasses. TOA longwave flux distributions were close to those from satellite with agreement of the mean value to within 0.4&#8201;%. From comparisons of Nd distributions to those from satellite it was found that the Nd mode from the model agreed with the higher of the two observed modes to within ~&#8201;15&#8201;%.

show abstract

An observation of sea‐spray microphysics by airborne Doppler radar

Cited by 9 publications

References 39 publications

On the upward flux of sea‐spray spume droplets in high‐wind conditions

On the upward flux of sea‐spray spume droplets in high‐wind conditions

The relative importance of macrophysical and cloud albedo changes for aerosol-induced radiative effects in closed-cell stratocumulus: insight from the modelling of a case study

The relative importance of macrophysical and cloud albedo changes for aerosol induced radiative effects in stratocumulus

Contact Info

Product

Resources

About