Sensitivity of the atmospheric lapse rate to solar cloud absorption in a radiative‐convective model

Abstract

[1] Previous radiative-convective model studies of the radiative forcing due to absorbing aerosols such as soot and dust have revealed a strong dependence on the vertical distribution of the absorbers. In this study, we extend this concept to absorption in cloud layers, using a one-dimensional radiative-convective model employing high, middle, and low cloud representations to investigate the response of the surface temperature and atmospheric lapse rate to increases in visible cloud absorption. The visible singlescattering albedo (ssa) of the clouds is prescribed, ranging from 1.0 to 0.6, where 0.99 is the minimum that would be expected from the presence of absorbing aerosols within the cloud drops on the basis of recent Monterey Area Ship Track (MAST) Experiment case studies. Simulations are performed with respect to both a constant cloud optical depth and an increasing cloud optical depth and as a function of cloud height. We find that increases in solar cloud absorption tend to warm the troposphere and surface and stabilize the atmosphere, while increases in cloud optical depth cool the troposphere and surface and slightly stabilize the atmosphere between the low cloud top and surface because of the increase in surface cooling. In the absence of considerations involving microphysical or cloud-climate feedbacks, we find that two conditions are required to yield an inversion from a solar cloud absorption perturbation: (1) The solar absorption perturbation must be included throughout the tropospheric clouds column, distributing the solar heating to higher altitudes, and (2) the ssa of the clouds must be 0.6, which is an unrealistically low value. The implication is that there is very little possibility of significant stabilization of the global mean atmosphere due to perturbation of cloud properties given current ssa values.INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution-urban and regional (0305); 1620 Global Change: Climate dynamics (3309); 3359 Meteorology and Atmospheric Dynamics: Radiative processes; KEYWORDS: solar cloud forcing, radiativeconvective model, indirect aerosol effect Citation: Erlick, C., and V. Ramaswamy, Sensitivity of the atmospheric lapse rate to solar cloud absorption in a radiative-convective model,

Absorbing aerosols over Asia: A Geophysical Fluid Dynamics Laboratory general circulation model sensitivity study of model response to aerosol optical depth and aerosol absorption

“…Since SSTs are prescribed and do not change relative to the BASE case, aerosol forcing affects the surface energy balance principally over land areas, hence our focus is on the land domains. The clear‐sky aerosol SFC forcing over land (Table 2) is roughly a factor of 2 greater than the all‐sky SFC DRF because clouds dominate the optical depth when present, causing aerosols to affect the surface primarily in cloud‐free conditions [ Erlick and Ramaswamy , 2003]. At the top of the atmosphere, with the exception of XChW, the all‐sky anthropogenic DRF shifts in sign from negative to positive when comparing clear‐sky with all‐sky forcing, particularly for the HOD simulations.…”

Temporal and spatial changes in estimated near‐surface air temperature lapse rates on Tibetan Plateau

“…Steeper LRs occur with higher levels of solar radiation (Hu, 1996;Erlick and Ramaswamy, 2003;Harlow et al, 2004). Higher wind speed also steepens LRs, especially at night (even close to dry adiabatic LR, −9.5 K/km), and moister atmospheres produce shallower LRs (close to moist adiabatic LR, −4.0 K/km) (Jain et al, 2008;Kirchner et al, 2013) Flow chart in this study continuous distribution and high resolution throughout the TP are still lacking.…”

Differing regional responses to a perturbation in solar cloud absorption in the SKYHI general circulation model

“…Like the RCM simulations of Erlick and Ramaswamy [2003], in the global mean there is a slight increase in water vapor (or precipitable water, PRECIP WATER) and an increase in atmospheric stability, which is reflected in the decrease in precipitation (RAIN+SNOW), soil moisture, evaporation and sublimation (EVAP+SUBL), and latent heat release from the surface (LH SFC). As in the RCM simulations, in the global mean the troposphere has warmed because of the input of SW flux, and the overall response is similar to that of the RCM, albeit with different physics considerations [ Erlick and Ramaswamy , 2003]. However, this does not render an equivalence between RCM and GCM simulations for this kind of a perturbation.…”

“…The optical depths of the clouds are left unperturbed. This is similar to the low clouds only perturbation with nominal cloud optical depths in the RCM of Erlick and Ramaswamy [2003], except that the cloud amount is allowed to vary with time in each grid box and horizontal dynamics also plays a part. Again for simplicity of interpretation, the model's sea surface temperatures (SSTs) are prescribed in a similar fashion to Chen and Ramaswamy [1995] (fixed from year to year, but seasonally varying within a specific year), so that in assessing the surface temperature response we focus on the land surfaces only.…”

“…(For the idealized experiment carried out here we increase the amount of absorption over 50% by using 0.99 instead.) Using a one dimensional radiative convective model (RCM), it was shown that in the absence of microphysical or cloud‐climate feedbacks, the resulting increase in solar heating within the cloud layer causes a warming of the troposphere and surface, an increase in water vapor, and a stabilization of the atmosphere [ Erlick and Ramaswamy , 2003]. With only low clouds perturbed, and no perturbation to the cloud optical depth, the calculated forcing due to this solar absorption in low clouds was 4.5 W m −2 , which is significant in comparison of estimated forcings due to anthropogenic greenhouse gases [ Ramaswamy et al , 2001].…”