Stratus clouds

Galloway, J.N. Likens, G.E. Hawley, M.E. Science, 1984,226, pp 829-831. Castillo, R. An Investigation of the Acidity of Stratus Cloud Water and Its Relationship to Droplet Distribution, pH of Rain and Weather Parameters, Ph.D. Thesis, Dept. Atmos. Sci., State University of New York, Albaity, NY, 1979. 

We see from this diagram that partial pressures of H2O at ordinary conditions range from very small values to perhaps 30 or 40 mbar. This corresponds to a mass concentration range up to about 25 g H20/m. In typical clouds, relatively little of this is in the condensed phase. Liquid water contents in the wettest of cumulus clouds are around a few grams per cubic meter ordinary mid-latitude stratus clouds have 0.3-1 g/m. ... 

FIGURE 8.19 Concentrations of major anions and cations in coastal stratus clouds at La Jolla Peak, California, on July 6, 1993 (adapted from Collett et al., 1994). 

Richards, L. W Airborne Chemical Measurements in Nighttime Stratus Clouds in the Los Angeles Basin, Atmos. Environ., 29, 27-46 (1995). 

Platnick and Twomey (1994) have applied Eq. (KK) to marine clouds off the coast of California and southern Africa, to fogs in central California, and to ship tracks. Figure 14.42 shows a typical range of susceptibilities as a function of cloud droplet size. The measured susceptibilities in these studies covered three orders of magnitude, from 5 X 10-5 cm3 for fogs to 0.8 X 10-3 cm3 for marine clouds off south Africa and 2 X 10 2 cm3 for thin stratus clouds off the California coast. Similarly, Taylor and McHaffie (1994) report cloud susceptibilities in the range from 10-4 to >8 X 10-3 at various locations around the world. The highest susceptibilities were those with the smallest aerosol particle concentrations below the cloud base. As the particle concentration increased beyond 500 cm3, the susceptibility was relatively constant at 5 X 10"4 cm3. This means that the addition of new particles to a relatively clean air mass is far more effective than for a polluted one in terms of the effect on clouds. In short,... 

FIGURE 14-42 Cloud susceptibilities (logarithmic scale) and cloud droplet radii for stratus clouds off Africa and California and from fogs in California (adapted from Platnick and Twomey, 1994). 

FIGURE 14-49 Absorption of light from an overhead sun by water associated with a 1-km stratus cloud with its top at an altitude of 2 km. The solid line is the absorption due to liquid water, the dashed line water vapor inside the cloud, and the dotted line water vapor in a column in the atmosphere (adapted from Davies et al., 1984). 

Figure 14.49 shows the absorption of light from an overhead sun by liquid cloud droplets, water vapor inside the cloud, and water vapor in a column in the atmosphere for a 1-km stratus cloud whose top is 2 km above the ground (Davies et al., 1984 see also Goldstein and Penner, 1964). There are small amounts of absorption in the tail end of the red region of the visible attributed to water vapor in and outside the cloud. The absorption increases into the near-IR (the region from 780 to 2500 nm or 12,800-4000 cm-1) and mid-IR (2.5-50 fim or 4000-200 cm-1) where liquid water in the cloud absorbs (e.g., see Evans and Puckrin, 1996). 

Figure 7 Transmission of the atmosphere containing a polluted stratus cloud with a varying amount of soot inclusion and disolved absorbers, normalised to clean cloudless conditions. Here f is the soot volume fraction in the cloud drops (from figure 7 of Erlick et al.l998)...

Clouds formed when the dew point is above the freezing point are Cumulus clouds and Stratus clouds. 

The interaction processes in the aerosol-cloud-radiation system that determine the indirect impact of aerosol on climate remain poorly studied, though they are an important factor in RF formation (the respective estimates vary between OWm-2 and —4.8Wm-2). The contribution to indirect climatic impact by aerosol due to lower-level stratus clouds is important since... 

Figure 26 Calculated relation between albedo and the number concentration of eloud droplets. The sloping line shows the relation between the albedo (at various levels of the atmosphere and globally) as a function of an increase in number concentration of cloud-droplets, A cd- The four ordinates show the perturbation in eloud-top albedo (left axis), TOA albedo above marine stratus (first right axis), global-mean albedo (second right axis), and global-mean eloud radiative forcing (far right axis). The fractional atmospheric transmittance of short-wave radiation above the eloud layer was taken as 76%. The dotted line indieates the perturbations resulting from a 30% inerease in Ned (Charlson et al., 1992) (reproduced by permission of American Association for the Advancement of Seience from Science,...

Cloud types often are classified based on altitude. High clouds have their bases above 7 km (23,000 ft) and include the wispy mare s tail clouds known as cirrus the cirrocumulus, known as mackerel sky and the layers of cirro-stratus. Middle clouds have altitudes between 2 and 7 km (6500 to 23,000 ft), and are either the rounded altocumulus or the layered altostratus. Low clouds have bases from near Earth s surface to about 2 km (6500 ft), and include stratocumulus, stratus, and nimbostratus. Nimbostratus clouds usually bring rain or snow. Clouds with vertical development extend from about 2 to 7 km or more, and include cumulonimbus (thunderhead clouds) and cumulus. 

DMS reactions in the troposphere are believed to lead to enhanced reflectivity of marine clouds [171] and thus DMS emissions may have a cooling influence on the atmosphere. One of the best demonstrations of the link between the natural atmospheric sulfur cycle and the physical climate system are the observations that link the satellite derived stratus cloud optical depth and observed DMS derived cloud condensation nuclei (CCN) concentrations at Cape Grim, Australia [175]. Statistical evidence indicates that the optical depth of the clouds is correlated with the number of CCN in the atmosphere. Thus, any UV-related changes at the surface of the ocean that result in the alteration in DMS flux to the atmosphere and the subsequent formation of CCN would also alter the atmospheric radiation budget for the affected region. 

The types of clouds depend on the season. During the cold season with its frequent inversions and low moisture content in air stratus clouds with small vertical thickness prevail. In the summer over the heated land convection processes are developing, thus, facilitating cumuli formation. 

Eeel Y, Pehkonen S and Hoeemann M (1993) Redox chemistry of iron in for and stratus clouds. 

The predictions presented above agree with measured concentration/size dependencies measured in clouds that are not heavily influenced by anthropogenic sources. Noone et al. (1988) sampled droplets from a marine stratus cloud and calculated that the volumetric mean solute concentration of the 9-18-pm droplets was a factor of 2.7 smaller than in the 18-23-pm droplets. Ogren et al. (1989) reported similar results for a cloud in Sweden. On the other hand, similar measurements for cloud and fog droplets in heavily polluted environments suggest that solute concentrations decrease with increasing droplet size (Munger et al. 1989 Ogren et al. 1992). No satisfactory explanation exists for such behavior. 

Develk, J. P. (1994) A model for cloud chemistry—a comparison between model simulations and observations in stratus and cumulus, Atmos. Environ. 28, 1665-1678. 

Hudson, J. G., and Frisbie, P. R. (1991) Cloud condensation nuclei near marine stratus, J. Geophys. Res. 96, 20795-20808. 

Ship tracks, linear features of high cloud reflectivity embedded in marine stratus clouds, result from aerosols emitted or formed from the exhaust of ships engines (Coakley et al. 1987 Scorer 1987 Radke et al. 1989 King et al. 1993) (Figure 24.15). Aircraft observations have confirmed enhanced droplet concentrations and decreased drop sizes in the ship tracks themselves as compared with the adjacent, unperturbed regions of the clouds (Radke et al. 1989 King et al. 1993 Johnson et al. 1996). 

---