Drizzle Suppression in Ship Tracks

Ferek, Ronald J.; Garrett, Timothy J.; Hobbs, Peter V.; Strader, Scott; Johnson, Doug; Taylor, Jonathan P.; Nielsen, K.; Ackerman, Andrew S.; Kogan, Yefim L.; Liu, Qingfu; Albrecht, Bruce A.; Babb, David M.

doi:10.1175/1520-0469(2000)057<2707:dsist>2.0.co;2

Cited by 103 publications

(78 citation statements)

References 43 publications

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“…4a, the 2-D continuous bin model predicts that the LWP increases with increasing aerosol concentration (by 6 g m −2 at the end of the simulations). This is in agreement with previous modeling studies (e.g., Albrecht, 1989;Ackerman et al, 2003;Wood et al, 2009) and in-situ observations (Radke et al, 1989;Ferek et al, 2000). The increase in LWP results from changes near cloud top to an increase in aerosol loading.…”

Section: Comparison Of Microphysics Schemessupporting

confidence: 92%

A continuous spectral aerosol-droplet microphysics model

Lebo

Seinfeld

2011

Atmos. Chem. Phys.

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Abstract.A two-dimensional (2-D) continuous spectral aerosol-droplet microphysics model is presented and implemented into the Weather Research and Forecasting (WRF) model for large-eddy simulations (LES) of warm clouds. Activation and regeneration of aerosols are treated explicitly in the calculation of condensation/evaporation. The model includes a 2-D spectrum that encompasses wet aerosol particles (i.e., haze droplets), cloud droplets, and drizzle droplets in a continuous and consistent manner and allows for the explicit tracking of aerosol size within cloud droplets due to collision-coalescence. The system of differential equations describing condensation/evaporation (i.e., mass conservation and energy conservation) is solved simultaneously within each grid cell. The model is demonstrated by simulating a marine stratocumulus deck for two different aerosol loadings (100 and 500 cm −3 ), and comparison with the more traditional microphysics modeling approaches (both 1-D bin and bulk schemes) is evaluated. The simulations suggest that in a 1-D bin microphysics scheme, without regeneration, too few particles are produced and hence the mode of the droplet size spectrum occurs at a larger size relative to the 2-D bin model results. Moreover, with regeneration, the 1-D scheme produces too many small droplets and thus shifts the mode toward smaller sizes. These large shifts in the droplet size distribution can potentially have significant effects on the efficiency of the collision-coalescence process, fall speeds, and ultimately precipitation.

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Section: Comparison Of Microphysics Schemessupporting

confidence: 92%

A continuous spectral aerosol-droplet microphysics model

Lebo

Seinfeld

2011

Atmos. Chem. Phys.

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“…The results from satellite data analysis agree with previous studies, e.g. from the MAST-experiment (Öström et al, 2000;Hobbs et al, 2000;Ferek et al, 2000). Figure 12 shows down-welling solar radiation at the surface below the clouds and reflected solar radiation at TOA, calculated by the method described in Sect.…”

Section: Microphysical and Optical Cloud Propertiessupporting

confidence: 89%

Impact of ship emissions on the microphysical, optical and radiative properties of marine stratus: a case study

Schreier

Kokhanovsky²,

Eyring³

et al. 2006

Atmos. Chem. Phys.

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Abstract. Modifications of existing clouds by the exhaust of ships are well-known but inadequately quantified impacts, which could contribute to climate change. The perturbation of a cloud layer by ship-generated aerosol changes the cloud reflectivity and is identified by long curves in satellite images, known as ship tracks. As ship tracks indicate a pollution of a very clean marine environment and also affect the radiation budget below and above the cloud, it is important to investigate their radiative and climatic effects. Satellitedata from MODIS on Terra are used to examine a scene from 10 February 2003 where ship tracks were detected close to the North American West-Coast. The cloud optical and microphysical properties are derived using a semi-analytical retrieval technique combined with a look-up-table approach. An algorithm is presented to distinguish ship-track-pixels from the unperturbed cloud pixels in the scene and from this the optical properties of the former are compared to those of the latter. Within the ship tracks a significant change in the droplet number concentration, the effective radius and the optical thickness are found compared to the unaffected cloud. The resulting cloud properties are used to calculate the radiation budget below and above the cloud. Assuming a mean solar zenith angle of 63 • for the selected scene, the mean solar surface radiation below the ship track is decreased by 43.2 Wm −2 and the mean reflectance at top of atmosphere (TOA) is increased by 40.8 Wm −2 . For the entire analyzed scene the ship emission decreases the solar radiation at the surface by 2.1 Wm −2 and increases the backscattered solar radiation at TOA by 2.0 Wm −2 , whereas no significant effect on thermal radiation was detected.

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“…This result is in accordance with the observations made by Rosenfeld (1999) and Ferek et al (2000) in which they show that smaller CER lead to an increase in LWP suppressing drizzle formation in smoke plumes and ship tracks. The suppression of drizzle enhances cooling below the cloud base because smaller droplets evaporate more quickly.…”

Section: Second Indirect Effectsupporting

confidence: 93%

Role of fine mode aerosols in modulating cloud properties over industrial locations in north India

Abish

Mohanakumar

2011

Ann. Geophys.

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Abstract. The influence of aerosols on cloud properties over North India which includes the Indo-Gangetic Plain has been investigated for the years 2000 to 2010. During the years 2004, 2009 and 2010 there has been an abrupt increase in fine mode aerosol optical depth (AOD) inducing a sharp decline in cloud effective radius (CER) in the month of January. The following monsoon during these years was a failure in the region considered for the study. In the year 2010, a highest AOD value of 0.35 was recorded in the month of January. In accordance with the aerosol indirect effect, this large increase in AOD resulted in a significant reduction in CER. The monsoon season in that year was deficient in the study region even though the rest of the country received above normal rainfall. For the years when CER diminished below 12 microns in the month of May, a delay in the advancement of monsoon towards North India is noted even after a normal or early onset in southern peninsula. Meanwhile, a rapid progression took place when it was 12 microns or above. During non-monsoon months an inverse relationship existed between cloud effective radius and liquid water path and a strong positive association occurred in the monsoon months. Present analysis suggests that the excessive aerosol loading and the associated aerosol indirect effects in the months prior to the monsoon season has an effect on the propagation and onset of the south west monsoon over the region.

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Drizzle Suppression in Ship Tracks

Cited by 103 publications

References 43 publications

A continuous spectral aerosol-droplet microphysics model

A continuous spectral aerosol-droplet microphysics model

Impact of ship emissions on the microphysical, optical and radiative properties of marine stratus: a case study

Role of fine mode aerosols in modulating cloud properties over industrial locations in north India

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