| Vol. 27, Issue 4 |
The joint NASA/NSF Coqui II sounding-rocket campaign was carried out in Puerto Rico during a two-month period beginning in February 1998. The goal of the investigation was to combine a comprehensive array of ground-based instrumentation with a series of in situ sounding rocket measurements in order to study the ionized and neutral layer phenomena that are common in the mesosphere and lower thermosphere, including sporadic E layers, intermediate layers, neutral turbulence layers, oxygen layers, and sudden sodium layers. The launches were carried out on the north coast of Puerto Rico at a temporary launch site located in proximity to the Arecibo Observatory incoherent scatter radar and lidar facilities. Other ground-based instrumentation included coherent scatter VHF and HF radars, optical imagers, and Fabry-Perot interferometers. The first results from the campaign are described in the special section in this issue. The results represent some of the most extensive lidar, incoherent scatter radar, and coherent scatter radar comparisons carried out so far. Hecht et al. [453] and Friedman et al. [449] show the close relationship between sudden sodium layers and sporadic E layers over a period of several months. Earle et al. [461] describe discreet sublayers of Fe+, Mg+, and NO+. In addition, Kelley and Gelinas [457] show the importance of the turbulent variations with height in determining the details in the vertical profiles. Larsen [445] notes that large winds and wind shears appear to be a common feature of the mesosphere and lower thermosphere region and are critical in organizing the turbulence and layered structure in that part of the atmosphere. The presence of such large winds and shears is also indicated by calculations based on measurements of the ionization density profiles, performed by Kelley et al. [465], which show the strong influence of space weather conditions. The results that are presented suggest a large-scale organization based on the wind structures with shear regions that extend over a significant fraction of a scale height and features that are persistent over periods of many hours. Küppers and Schneider [513] report discovery of singly ionized chlorine (Cl+) in the Io plasma torus. The Cl+ emission is found to peak at the same jovicentric distance as the emissions of the major torus ions. Moreover, since chlorine is not a known constituent of Jupiter's atmosphere, the authors suggest that Io's atmosphere is the probable source for the observed Cl+. They note that since chlorine is a relatively reactive gas, it could play an important role in Io's atmospheric chemistry. They propose that sodium chloride (crystalline orgaseous) or hydrogen chloride may be the source of Cl+. According to standard models of stellar evolution, 4 billion years ago the sun was about 25% cooler than it is today, and terrestrial and Martian temperatures were below freezing. Because the faint, young sun could not have melted ice into liquid water until about 1 billion years ago, Earth should have been lifeless for billions of years. But geological evidence shows that there was plenty of liquid water as far back as about 4 billion years ago. One alternative model for solar evolution, with a brighter, slightly more massive, younger sun, invokes mass loss (5%-10%) through a declining solar wind. But Gaidos et al. [501] use results of deep radio observations of a nearby 0.3 billion-year-old solar-mass star, selected on the basis of its analogy to the early Sun, and find that the early solar wind for this young Sun would not produce enough mass loss as required by the alternative model. Within the United States and adjacent coastal waters, the greatest number of thunderstorm days in December- February, approximately 10 in a typical winter, occurs along the Southeast Gulf Coast and East Texas to the Florida Panhandle and over the warm waters of the Gulf Stream. Goodman et al. [541] show that the northern Gulf of Mexico basin experiences an increase in lightning activity during ENSO events. The authors use two data sets-a 10-year (1989-1999) database of U.S. cloud-to-ground lightning activity and total (in-cloud and cloud-to-ground) lightning activity data recorded from space by a NASA launched sensor-to show that during 1997-1998, there is a 100%-150% increase in lightning days year-to-year and a nearly 200% increase in lightning hours (compared to 1996-1997 and 1998-1999) in the basin. They attribute these changes to an enhanced synoptic-scale forcing associated with ENSO and a stronger than normal upper-level jet stream. They also find good agreement between most of the recent warm ENSO events and cyclogenesis within the basin. Polar firns contain air bubbles that can be used to reconstruct trends in atmospheric trace gases. To date the air, however, the effective diffusivity of the gases must be known. Fabre et al. [557] compare the effective diffusivity profiles for three gases in firns (experiencing different climatic conditions) using both laboratory experiments and inverse modeling of gas diffusion. The authors perform measurements on samples from two different firns: an Antarctic firn and an alpine firn. They conclude that diffusivities measured on small firn samples cannot directly describe a firn's tortuosity profile when continuous porosity variations in the firn are not known. The inverse model should be used instead. |
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