3,868 research outputs found
A comparison of mean winds and gravity wave activity in the northern and southern polar MLT
Mean winds and waves observed in the mesosphere and lower thermosphere with MF radars located at Davis (69°S, 78°E) and Poker Flat (65°N, 147°W) are compared. Measurements covering the period from 1999 to mid 2000 show differences in the strength of the horizontal wind fields. In the southern hemisphere the zonal and meridional winds reach their maximum values near the summer solstice, but are delayed by 2–3 weeks in the northern hemisphere. Gravity wave variances also show significant differences, as do the strength of vertical velocities.Andrew Dowdy and Robert A. Vincent, Kiyoshi Igarashi and Yasuhiro Murayama, Damian J. Murph
Gravity waves and high-altitude CO ice cloud formation in the Martian atmosphere
We present the first general circulation model simulations that quantify and
reproduce patches of extremely cold air required for CO condensation and
cloud formation in the Martian mesosphere. They are created by subgrid-scale
gravity waves (GWs) accounted for in the model with the interactively
implemented spectral parameterization. Distributions of GW-induced temperature
fluctuations and occurrences of supersaturation conditions are in a good
agreement with observations of high-altitude CO ice clouds. Our study
confirms the key role of GWs in facilitating CO cloud formation, discusses
their tidal modulation, and predicts clouds at altitudes higher than have been
observed to date.Comment: Accepted for publication in Geophysical Research Letters (GRL
Information Length as a Useful Index to Understand Variability in the Global Circulation
With improved measurement and modelling technology, variability has emerged
as an essential feature in non-equilibrium processes. While traditionally, mean
values and variance have been heavily used, they are not appropriate in
describing extreme events where a significant deviation from mean values often
occurs. Furthermore, stationary Probability Density Functions (PDFs) miss
crucial information about the dynamics associated with variability. It is thus
critical to go beyond a traditional approach and deal with time-dependent PDFs.
Here, we consider atmospheric data from the Whole Atmosphere Community Climate
Model (WACCM) model and calculate time-dependent PDFs and the information
length from these PDFs, which is the total number of statistically different
states that a system passes through in time. Time-dependent PDFs are shown to
be non-Gaussian in general, and the information length calculated from these
PDFs shed us a new perspective of understanding variabilities, correlation
among different variables and regions. Specifically, we calculate
time-dependent PDFs and information length and show that the information length
tends to increase with the altitude albeit in a complex form. This tendency is
more robust for flows/shears than temperature. Also, much similarity among
flows and shears in the information length is found in comparison with the
temperature. These results also suggest the importance of high
latitude/altitude in the information budge in the Earth's atmosphere, the
spatial gradient of the information as a useful proxy for the transport of
physical quantities.Comment: 15 pages, 5 figure
Simultaneous rocket and MST radar observation of an internal gravity wave breaking in the mesosphere
In June, 1983, the Structure and Atmospheric Turbulence Environment (STATE) rocket and Poker Flat Mesophere-Stratosphere-Troposphere radar campaign was conducted to measure the interaction between turbulence, electron density and electron density gradient that has produced unusually strong MST radar echoes from the summer mesosphere over Poker Flat, Alaska. Analysis or radar wind measurements and a concurrent wind and temperature profile obtained from a rocket probe carrying a three-axis accelerometer are given. The two data sets provide a fairly complete (and in some cases, redundant) picture of the breaking (or more correctly, the saturation) of a large-amplitude, low-frequency, long-wavelength internal gravity wave. The data show that small-scale turbulence and small-scale wave intensity is greatest at those altitudes where the large-scale wave-induced temperature lapse rate is most negative or most nearly unstable, but the wind shear due to the large-scale wave is a minimum. A brief review of linear gravity-wave theory is presented as an aid to the identification of the gravity-wave signature in the radar and rocket data. Analysis of the time and height cross sections of wind speed and turbulence intensity observed by the Poker Flat MST radar follows. Then, the vertical profile of temperature and winds measured by a rocket probe examined. Finally, the use of the independent data sets provided by the rocket and the radar are discussed and implications for theories of wave saturation are presented
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