Air motions in the tropical stratosphere deduced from satellite tracking of horizontally floating balloons

Between June and November of 1970, 26 constant level balloons were released from Ascension Island (8 S) for flight at 30 and 50 mb. The balloons were positioned by the Interrogation, Recording and Location System (IRLS) aboard the Nimbus D satellite. In general, balloon positioning appeared to be accurate to within a few kilometers, although occasionally there was doubt as to whether the balloon position was to the right or left of the satellite subtrack. Eight of the flights at 50 mb and three of the flights at 30 mb were tracked for more than one month, and one 50 mb flight was tracked continuously for more than 5 months while making 7 circumnavigations of the Earth. From the satellite-determined 12-hourly balloon positions in the tropics, 223 smoothed 24-hour-average zonal and meridional winds were obtained at 30 mb and 693 such winds were obtained at 50 mb. Near the equator the balloons moved from east to west at a speed of about 23 ms^–1 at 50 mb and 28 ms^–1 at 30 mb, while undergoing a mean northward drift of approximately 0.1 ms^–1. The northward drift was a maximum in the Northern Hemisphere winter, suggesting a weak upward extension of the Hadley Cell to 50 mb. Superimposed on this drift were oscillations in meridional velocity of about 2-month period, with these oscillations also most pronounced in the Northern Hemisphere winter. Small (1–3 ms^–1) short-period fluctuations in meridional velocity were evident directly above the equator at 50 mb. These waves appear to move westward at speeds of 30–40 ms^–1 and to have a wavelength of about 90° longitude. They were responsible for transporting small amounts of westerly momentum into the winter hemisphere. Fluctuations in zonal velocity (Kelvin waves) were also delineated by flights near the equator. These waves appear to move eastward at speeds of 30–40 ms^–1 and to have a wavelength of 360° longitude. Some comparisons are made between these IRLS data and the data obtained from GHOST balloon flights at the same heights in early 1969.     

Coherent radio emission from pulsars

Our knowledge of radio pulsars is reviewed with particular emphasis on properties of radio emission that are relevant to an understanding of the emission mechanism. We discuss the tendency for emission to occur in two orthogonal modes of polarization, observational limits on the location of the emission region, and the issue of whether coherence is established by a broadband or a narrowband mechanism.Proceedings of the NASA/JPL Workshop on the Physics of Planetary and Astrophysical Magnetospheres.     

Estimating irrigation water use and withdrawal of ground water on the High Plains,U.S.A.

In four decades following the Dust Bowl days of the 1930's, extensive areas of dry farming and rangeland on the semi-arid U.S. High Plains were transformed into a vast region of irrigated oases, producing meat and grain for much of the world. The agricultural economy has experienced such rapid growth in part because of the availability of ground water and because of development of new irrigation technology to use that water for agriculture. However, more water is being used than is being replaced. To estimate both the volume of water withdrawn and the regional scope of the problem a technique has been developed that combines multispectral data from Earth-orbiting satellite with known pumpage data for the same growing season. The location and extent of irrigated cropland—some with different crops watered at different times—is inventoried using computer-assisted analysis of the data from Landsat. The amount of water used is estimated by multiplying and summing surface area of irrigated agriculture and the average measured pumpage from sampled sites. Published findings to date are cited in the Selected References. All suggest transferability of a promising technology to the study of land transformation processes elsewhere.     

NASA's new Mars Exploration Program: the trajectory of knowledge

NASA's newly restructured Mars Exploration Program (MEP) is finally on the way to Mars with the successful April 7 launch of the 2001 Mars Odyssey Orbiter. In addition, the announcement by the Bush Administration that the exploration of Mars will be a priority within NASA's Office of Space Science further cements the first decade of the new millennium as one of the major thrusts to understand the "new" Mars. Over the course of the past year and a half, an integrated team of managers, scientists, and engineers has crafted a revamped MEP to respond to the scientific as well as management and resource challenges associated with deep space exploration of the Red Planet. This article describes the new program from the perspective of its guiding philosophies, major events, and scientific strategy. It is intended to serve as a roadmap to the next 10-15 years of Mars exploration from the NASA viewpoint. [For further details, see the Mars Exploration Program web site (URL): http://mars.jpl.nasa.gov]. The new MEP will certainly evolve in response to discoveries, to successes, and potentially to setbacks as well. However, the design of the restructured strategy is attentive to risks, and a major attempt to instill resiliency in the program has been adopted. Mars beckons, and the next decade of exploration should provide the impetus for a follow-on decade in which multiple sample returns and other major program directions are executed. Ultimately the vision to consider the first human scientific expeditions to the Red Planet will be enabled. By the end of the first decade of this program, we may know where and how to look for the elusive clues associated with a possible martian biological record, if any was every preserved, even if only as "chemical fossils."     

Water and Volatile Inventories of Mercury,Venus, the Moon,and Mars

We review the geochemical observations of water, \(\mbox{D}/\mbox{H}\) and volatile element abundances of the inner Solar System bodies, Mercury, Venus, the Moon, and Mars. We focus primarily on the inventories of water in these bodies, but also consider other volatiles when they can inform us about water. For Mercury, we have no data for internal water, but the reducing nature of the surface of Mercury would suggest that some hydrogen may be retained in its core. We evaluate the current knowledge and understanding of venusian water and volatiles and conclude that the venusian mantle was likely endowed with as much water as Earth of which it retains a small but non-negligible fraction. Estimates of the abundance of the Moon’s internal water vary from Earth-like to one to two orders of magnitude more depleted. Cl, K, and Zn isotope anomalies for lunar samples argue that the giant impact left a unique geochemical fingerprint on the Moon, but not the Earth. For Mars, an early magma ocean likely generated a thick crust; this combined with a lack of crustal recycling mechanisms would have led to early isolation of the Martian mantle from later delivery of water and volatiles from surface reservoirs or late accretion. The abundance estimates of Martian mantle water are similar to those of the terrestrial mantle, suggesting some similarities in the water and volatile inventories for the terrestrial planets and the Moon.