Amplitude enhancements in Antarctic MF radar echoes

Enhancements in the amplitude of returns from a medium-frequency (MF) radar at Davis, Antarctica, have been identified and their potential use as a measure of polar mesosphere summer echoes (PMSE) has been explored. A method for finding these enhancements has been applied to data spanning the period from mid-1995 to the end of 1997. The character of these enhancements on short and long timescales has been studied, and factors that may affect their detection have been considered. It has been found that they are short-lived (2 min or less being most common) and largely limited to the months around summer. Apart from describing the character of these amplitude enhancements, this study illustrates the potential pitfalls associated with identifying a proxy measure of PMSE.D. J. Murphy, R. A. Vincenthttp://cat.inist.fr/?aModele=afficheN&cpsidt=85383

Part One: The Man Who Loved Cities

Part One: The Man Who Loved Cities -- Whyte on Whyte: A Walk in the City / Eugenie L. Birch -- Holly Whyte’s Journalism of Place / Charles E. Little -- The Energizer / Ann Louise Strong -- Sowing the Seeds / Thomas Balsley -- The Wit and Wisdom of Holly Whyte / Gathered by Albert LaFarge

Magma plumbing systems: a geophysical perspective

Over the last few decades, significant advances in using geophysical techniques to image the structure of magma plumbing systems have enabled the identification of zones of melt accumulation, crystal mush development, and magma migration. Combining advanced geophysical observations with petrological and geochemical data has arguably revolutionised our understanding of, and afforded exciting new insights into, the development of entire magma plumbing systems. However, divisions between the scales and physical settings over which these geophysical, petrological, and geochemical methods are applied still remain. To characterise some of these differences and promote the benefits of further integration between these methodologies, we provide a review of geophysical techniques and discuss how they can be utilised to provide a structural context for and place physical limits on the chemical evolution of magma plumbing systems. For example, we examine how Interferometric Synthetic Aperture Radar (InSAR), coupled with Global Positioning System (GPS) and Global Navigation Satellite System (GNSS) data, and seismicity may be used to track magma migration in near real-time. We also discuss how seismic imaging, gravimetry and electromagnetic data can identify contemporary melt zones, magma reservoirs and/or crystal mushes. These techniques complement seismic reflection data and rock magnetic analyses that delimit the structure and emplacement of ancient magma plumbing systems. For each of these techniques, with the addition of full-waveform inversion (FWI), the use of Unmanned Aerial Vehicles (UAVs) and the integration of geophysics with numerical modelling, we discuss potential future directions. We show that approaching problems concerning magma plumbing systems from an integrated petrological, geochemical, and geophysical perspective will undoubtedly yield important scientific advances, providing exciting future opportunities for the volcanological community

First polar mesosphere summer echoes observed at Davis, Antarctica (68.6 degrees S)

Copyright 2004 by the American Geophysical Union.We report the first observations of polar mesosphere summer echoes (PMSE) above the high-latitude Southern Hemisphere (SH) station Davis, Antarctica (68.6°S, 78.0°E geographic; 74.6°S magnetic). Observations were obtained using a 55 MHz atmospheric radar, the first stage of which was commissioned late in the austral summer of 2002–2003. The radar commenced mesosphere observations with approximately 20 kW of transmitted power in October 2003. PMSE were recorded from 19 November to 3 December 2003 and, after a break in radar operation, from 27 January to 21 February 2004. We present the initial seasonal and diurnal occurrence morphology from 180 hours of Davis PMSE observations. Our initial findings reveal that SH PMSE show similar backscatter echo characteristics and occurrence properties to those reported for the Northern Hemisphere (NH).R. J. Morris, D. J. Murphy, I. M. Reid, D. A. Holdsworth, and R. A. Vincen

Comment on the Paper “On the influx of small comets into the Earth's upper atmosphere II. Interpretation” by L. A. Frank, J. B. Sigwarth and J. D. Graven

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96266/1/grl3191.pd

First in situ temperature measurements at the Antarctic summer mesopause

The Arctic summer mesopause at ∼88 km is the coldest-known place (∼130 K) in the terrestrial atmosphere and is ∼60 K colder in summer than winter. Indirect evidence has suggested that the summer mesopause temperatures in the Antarctic are a few Kelvin warmer than in the Arctic. However, reliable measurements have not been available at southern high latitudes to verify this. We report the very first in situ temperature observations in the summer mesosphere from Antarctica based on rocket-borne falling spheres launched from Rothera (68°S, 68°W). The first of 24 successful launches, on 5 January 1998, showed a mesopause temperature of 129 K at 87 km, surprisingly close to northern hemisphere (NH) mean summer values. During January the mesospheric temperatures are similar to the northern summer, but the difference increases to several Kelvin in Februar

Polar mesosphere and lower thermosphere dynamics: 1. Mean wind and gravity wave climatologies

Mean wind and gravity wave climatologies are presented for the polar mesosphere and lower thermosphere (MLT). The data were derived using MF radars at Davis (69°S, 78°E) and Syowa (69°S, 40°E) in the Antarctic and Poker Flat (65°N, 147°W) and Andenes (69°N, 16°E) in the Arctic. The dynamics of the Antarctic MLT are found to be significantly different from the Arctic MLT. Summer maxima in both the westward and equatorward winds occur closer to the solstice in the Antarctic than in the Arctic. The greater symmetry around the solstice suggests radiative effects may play a greater role in controlling the state of the Antarctic MLT than in the Arctic, where dynamical effects appear to be more important. Gravity wave observations also suggest that wave drag may be greater in the Arctic than in the Antarctic. The equatorward flow near the mesopause persists later in summer in the Arctic than in the Antarctic, as do observations of polar mesospheric clouds and polar mesospheric summer echoes. All three phenomena begin at about the same time in each hemisphere, but end later in the Arctic than in the Antarctic. It is proposed that the magnitude of the meridional winds can be used as a proxy for gravity wave driving and the consequent adiabatic cooling in the MLT. Seasonal variations in gravity wave activity are predominately combinations of annual and semiannual components. Significant hemispheric differences are observed for both the timing and magnitude of these seasonal variations. Copyright 2007 by the American Geophysical Union.Andrew J. Dowdy, Robert A. Vincent, Masaki Tsutsumi, Kiyoshi Igarashi, Yasuhiro Murayama, Werner Singer, Damian J. Murph