Stenchikov and Robock (1995)
Stenchikov, Georgiy L. and Alan Robock, 1995: Diurnal
asymmetry of climatic response to increased CO2 and aerosols:
forcings and feedbacks. J. Geophys. Res., 100, 26,211-26,227.
ABSTRACT:
To examine the causes of the observed diurnally-asymmetric
climate change over land, the roles of different physical mechanisms
are evaluated using a new radiative-convective model. This model
explicitly calculates a complete set of physical processes, including
the water vapor distribution, clouds, transports in the turbulent
boundary layer, and convection. Calculations were carried out for
midlatitude summer and winter and for tropical spring conditions
taking into account the most important climate forcings: CO2
increase, tropospheric aerosol pollution, and the combined case
with simultaneous CO2 and aerosol effects.
We find that feedbacks in the climate system are more important
than forcings in producing diurnal asymmetry. The water vapor-shortwave
feedback dominates the diurnal distribution of the
response. For all cases with warming, the diurnal temperature
range (DTR) decreases, not due to the greenhouse effect of water
vapor, but as a result of more intensive absorption of the solar
radiation in the near infrared by water vapor and cloud water in a
warmer, wetter climate independent of the type of forcing. Aerosol
reflection and absorption of solar radiation cool the surface and
decrease DTR directly, but the negative daytime water vapor
feedback virtually cancels out the diurnal asymmetry. In the
combined case, with 50% CO2 content increase combined with
tropospheric aerosol pollution, which is not far from the current
observed conditions over land, the greenhouse warming raises the
temperature enough that the direct aerosol effect decreases the
DTR. In all cases the time and spatial redistribution of clouds have
a significant impact on the climate sensitivity and diurnal cycle. As
in the observations, increasing of cloudiness and water vapor
content occurs with decreasing of the DTR. In our model, the
cloudiness and water vapor changes are produced by the same
forcings that lower the DTR; they are not independent causes of
changes of the DTR, but rather are important internal feedback
mechanisms.
![](col_line.gif)
Prepared by Alan Robock (robock@envsci.rutgers.edu ) -
Last updated on April 21, 1999