star pdf file

Northern Hemisphere (NH) ozone flux to be significantly larger (approximately 24\%) than that calculated in the Southern
Hemisphere (SH) during the year 2000. This diagnostic method makes it possible to separate dynamical aspects of transport
from the seasonal cycle of ozone in the lowermost stratosphere and explain the hemispheric difference in the ozone flux. The
SH total horizontal area of exchange is equal to or slightly greater than the area of exchange in the NH throughout an annual
cycle. The mean changes in potential vorticity of parcels near the tropopause are also similar or slightly greater in the SH,
suggesting that NH and SH downward total mass transport to the troposphere are comparable. These results imply that the
greater NH ozone flux is mostly due to the amount of ozone available for exchange rather than net hemispheric dynamical
differences near the tropopause level.
Author
Northern Hemisphere; Ozone; Southern Hemisphere; Tropopause; Wind (Meteorology)
20030025440 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Co-Seismic Mass Dislocation and its Effect on Earth’s Rotation and Gravity
Chao, B. F.; Gross, R. S.; January 2002; 1 pp.; In English; IERS Workshop on Combination Research and Global Geophysical
Fluids, 18-21 Nov. 2002, Munich, Germany; No Copyright; Avail: Other Sources; Abstract Only
Mantle processes often involve large-scale mass transport, ranging from mantle convection, tectonic motions, glacial
isostatic adjustment, to tides, atmospheric and oceanic loadings, volcanism and seismicity. On very short time scale of less
than an hour, co-seismic event, apart from the shaking that is the earthquake, leaves behind permanent (step-function-like)
dislocations in the crust and mantle. This redistribution of mass changes the Earth’s inertia tensor (and hence Earth’s rotation
in both length-of-day and polar motion), and the gravity field (in terms of spherical harmonic Stokes coefficients). The
question is whether these effects are large enough to be of any significance. In this paper we report updated calculation results
based on Chao & Gross (1987). The calculation uses the normal mode summation scheme, applied to nearly twenty thousand
major earthquakes that occurred during 1976-2002, according to source mechanism solutions given by the Harvard Central
Moment Tensor catalog. Compared to the truly large ones earlier in the century, the earthquakes we study are individually all
too small to have left any discernible signature in geodetic records of Earth rotation or global gravity field. However, their
collective effects continue to exhibit an extremely strong statistical tendencies. For example, earthquakes conspire to decrease
J2 and J22 while shortening LOD, resulting in a rounder and more compact Earth. Strong tendency is also seen in the
earthquakes trying to nudge the Earth rotation pole towards approximately 140 degrees E, roughly opposite to the observed
polar drift direction. The geophysical significance and implications will be further studied.
Author
Earth Rotation; Gravitation; Seismology; Volcanology; Geophysics; Earth Mantle
20030025661 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Time-Variable Gravity from Space: Quarter Century of Observations, Mysteries, and Prospects
Chao, Benjamin F.; [2003]; 1 pp.; In English; Workshop on GPS Meteorology: Ground-Based and Space-Borne Applications,
14-17 Jan. 2003, Tsukuba, Japan; No Copyright; Avail: Other Sources; Abstract Only
Any large mass transport in the Earth system produces changes in the gravity field. Via the space geodetic technique of
satellite-laser ranging in the last quarter century, the Earth’s dynamic oblateness J2 (the lowest-degree harmonic component
of the gravity field) has been observed to undergo a slight decrease -- until around 1998, when it switched quite suddenly to
an increase trend which has continued to date. The secular decrease in J2 has long been attributed primarily to the post-glacial
rebound in the mantle; the present increase signifies an even larger change in global mass distribution whose J2 effect
overshadows that of the post-glacial rebound, at least over interannual timescales. Intriguing evidences have been found in the
ocean water distribution, especially in the extratropical Pacific basins, that may be responsible for this J2 change. New
techniques based on satellite-to-satellite tracking will yield greatly improved observations for time-variable gravity, with much
higher precision and spatial resolution (i.e., much higher harmonic degrees). The most important example is the GRACE
mission launched in March 2002, following the success of the CHAMP mission. In addition, although less precise than
GRACE, the GPS/Meteorology constellation mission COSMIC, with 6 mini-satellites to be launched in late 2005, is expected
to provide continued and complementary time-variable gravity observations. Such observations are becoming a new and
powerful tool for remote sensing of geophysical fluid processes that involve larger-scale mass transports.
Author
Earth Gravitation; Gravitational Fields; Satellite Laser Ranging; Mass Distribution; Gravity Anomalies; Mass Transfer
69