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The lightness of water vapor helps to stabilize tropical climate.
Moist air is lighter than dry air at the same temperature, pressure, and volume because the molecular weight of water is less than that of dry air. We call this the vapor buoyancy effect. Although this effect is well documented, its impact on Earth's climate has been overlooked. Here, we show that the lightness of water vapor helps to stabilize tropical climate by increasing the outgoing longwave radiation (OLR). In the tropical atmosphere, buoyancy is horizontally uniform. Then, the vapor buoyancy in the moist regions must be balanced by warmer temperatures in the dry regions of the tropical atmosphere. These higher temperatures increase tropical OLR. This radiative effect increases with warming, leading to a negative climate feedback. At a near present-day surface temperature, vapor buoyancy is responsible for a radiative effect of 1 W/m2 and a negative climate feedback of about 0.15 W/m2 per kelvin
Testing the Hypothesis that the MJO is a Mixed Rossby-Gravity Wave Packet
The Madden Julian oscillation (MJO), also known as the intraseasonal oscillation (ISO), is a planetary-scale mode of variation in the
tropical Indian and western Pacific Oceans. Basic questions about the
MJO are why it propagates eastward at ~5 m s^(-1), why it
lasts for intraseasonal time scales, and how it interacts with the fine
structure that is embedded in it. This study will test the hypothesis
that the MJO is not a wave but a wave packet-the interference pattern
produced by a narrow frequency band of mixed Rossby gravity (MRG)
waves. As such, the MJO would propagate with the MRG group velocity,
which is eastward at ~5 m s^(-1) Simulation with a 3D model
shows that MRG waves can be forced independently by relatively
short-lived, eastward- and westward-moving disturbances, and the MRG
wave packet can last long enough to form the intraseasonal variability.
This hypothesis is consistent with the view that the MJO is episodic,
with an irregular time interval between events rather than a periodic
oscillation. The packet is defined as the horizontally smoothed
variance of the MRG wave-the rectified MRG wave, which has features in
common with the MJO. The two-dimensional Fourier analysis of the NOAA
outgoing longwave radiation (OLR) dataset herein indicates that there
is a statistically significant correlation between the MJO amplitude
and wave packets of MRG waves but not equatorial Rossby waves or Kelvin
waves, which are derived from the Matsuno shallow water theory.
However, the biggest absolute value of the correlation coefficient is
only 0.21, indicating that the wave packet hypothesis explains only a
small fraction of the variance of the MJO in the OLR data
Regularity Criteria for Navier-Stokes Equations with Slip Boundary Conditions on Non-flat Boundaries via Two Velocity Components
H.-O. Bae and H.J. Choe, in a 1997 paper, established a regularity criteria
for the incompressible Navier-Stokes equations in the whole space based
on two velocity components. Recently, one of the present authors extended this
result to the half-space case Further, this author in collaboration
with J. Bemelmans and J. Brand extended the result to cylindrical domains under
physical slip boundary conditions. In this note we obtain a similar result in
the case of smooth arbitrary boundaries, but under a distinct, apparently very
similar, slip boundary condition. They coincide just on flat portions of the
boundary. Otherwise, a reciprocal reduction between the two results looks not
obvious, as shown in the last section below.Comment: 15 page
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