Magnetic probes are used to study the hydromagnetic interaction between a shockwave and a magnetic field. Radio frequency radiations resulting from the interaction have been observed. This creation in the laboratory of electromagnetic radiation from plasma should lead to a better understanding of electromagnetic processes which occur in the upper atmosphere (page 140).

is to provide one second and one minute pulses derived from the 1 Mc/s standard frequency on a fail-safe basis. Instrumentation was essentially completed during the past year and component units will be integrated into the clock system early in the next year.

UPPER ATMOSPHERE AND SPACE PHYSICS

The research program in upper atmosphere and space physics recognizes the urgent need to increase the knowledge and understanding of the physical properties and processes in the media surrounding the earth and in interplanetary space. Such knowledge and understanding is essential to the expanding application of radio communication in the space age.

ometers.

Preliminary Measurements of Electron Densities to 1,200 KilA new ionospheric research facility, based on the incoherent scatter of radio waves from free electrons, will provide the Bureau with a powerful and very sensitive research tool for important ground-based observations of the ionosphere, exosphere, interplanetary medium, and the sun. This major constructional effort is now underway at the new Jicamarca Radio Observatory near Lima, Peru, and important new advances are anticipated as soon as the 6 megawatt peak-power radar system is fully operational, probably during late FY 1962. Already one-half of the huge 18,000-dipole broadside antenna has been completed. Preliminary observations using part of the antenna system, and a relatively low-power transmitter, have given several electron density profiles to heights of 1,200 kilometers. These preliminary observations indicate that the decay of electron density with height above the maximum of the F region is usually exponential for several hundred kilometers. On several occasions a rather abrupt discontinuity has been observed in this exponential decay, in that, at great heights, the ionization is found to decay much more slowly than in the first several hundred kilometers above the peak of the F layer.

Radiation Produced from a Plasma. Plasmas produced by a highvelocity shockwave traveling at speeds in excess of Mach 100 in helium have been studied in the laboratory in the presence of a transverse magnetic field. Radiofrequency radiations resulting from the hydromagnetic interaction between the shockwave and the magnetic field have been observed. This creation in the laboratory of electromagnetic radiation from plasmas is a major step towards duplicating under controlled conditions electromagnetic processes which occur in the upper atmosphere. An additional important advance has been the development of a high-speed camera, capable of operating at a rate in excess of one hundred million frames per second and designed to study the luminous phenomena in the shockwaves.

Investigations in Particle Processes. Normal HF communications are notoriously unreliable at high latitudes due to disturbances resulting from bombardment of the upper atmosphere by energetic particles guided to these regions by the geomagnetic field. A major advance was made in studying this field when a 10 Mc/s riometer system was designed and constructed to measure cosmic noise absorption. This system records continuously the cosmic noise strength on both circular polarizations, and offers the advantages over earlier systems of a tenfold improvement in sensitivity, together with a greater dynamic range and an indication of the height at which the absorption occurs.

In coopera

Cosmic Noise Study at USSR Mirny Base, Antarctica. tion with USSR scientists, an important quantitative study of cosmic noise absorption as observed in the high southern latitudes was undertaken. This work will not only produce important data for the southern hemisphere, but it will also permit the determination of the relationships between absorption events occurring simultaneously in the two polar regions.

Satellite Radio Signals Used to Study Structure of Ionosphere. Communication with vehicles in space poses difficulties since signals from space as received on earth are perturbed by irregularities in the electron density of the ionosphere. By studying radio signals received from satellites it has been possible to measure the ionospheric electron content and irregularities above the region of maximum electron density. Previous studies of signals from radio stars and satellites provided evidence of ionospheric irregularities which are 100 to 500 km in horizontal extent, and which occur during daylight hours on about one-third of all days. The current studies include investigations of the size, shape and motion of these irregularities as observed at separate multiple observing stations.

This

Meteor Burst Propagation Observations Successful. A full scale field observational program was conducted to provide statistical information on the radio energy scattered by transient meteor ionization. information is of great importance in studying the feasibility of meteor-burst communication between widely separated points, and in designing appropriate communication equipment. Measurements of propagation characteristics of transmissions at 30, 50, and 74 Mc/s were conducted over three paths of similar length. Two paths, crossing at right angles at the midpoint, were used in the U.S. to determine the dependence of meteor echoes on path orientation. The third path, in Alaska, was used to identify and measure meteor propagation characteristics peculiar to the auroral region. With successful completion of the field observations, the digitized data are now being analyzed to determine the pertinent propagation parameters.

Observatory Installed at Maui, Hawaii. The Bureau and the High Altitude Observatory of the University of Colorado have cooperated for some time in a study of the zodiacal light. Recently the collaboration has been extended to include the Hawaii Institute of Geophysics. An observatory has been established with National Aeronautical and Space Administration support on Mount Haleakala, Maui, Hawaii. The program includes, in addition to studies of the zodiacal light, systematic observations of the airglow.

Of particular interest is a strong correlation between the intensity of the atomic oxygen radiation (6300 A) and certain ionospheric parameters observed by the NBS ionosonde on the island of Maui. It has been found that the red (6300 A) line airglow intensities can be quite accurately predicted by a formula involving the parameters foF2 and h'F on the ionograms. The nature of the correlation supports the hypothesis that the red line is due to excitation of atomic oxygen by a photochemical reaction involving either O and electrons or NO+ and electrons.

The photometric observations cover the entire sky and extend over a region of radius some 1,000 kilometers, in contrast with the ionosonde vertical soundings which are essentially overhead. The two techniques thus serve to complement each other and extend the scope of the investigation of the ionosphere.

A mobile satellite observing station, in conjunction with permanent facilities at Table Mesa, is being used to study ionospheric irregularities and their effect on the reception of satellite signals (page 141).

In mid-latitudes the relationship between the 6300-A emission and the ionosphere is less clear and it seems that the photochemical reaction is only one of several effective mechanisms. The results in the tropics may thus serve to give information clarifying ionospheric processes which occur in mid-latitudes.

Numerical Representation of the Ionosphere. Further work under this program has provided the first automatic computer methods for predicting long-term changes in useful frequencies for ionosphere radio communication systems. The methods used incorporate recent advances in applied mathematics and statistics in such a way as to respect as far as possible the empirical knowledge accumulated in ionespheric studies. The method developed provides important flexibility in solving problems of ionospheric radio propagation by treating separately the three basic areas involved: ionosphere mapping, correlation of ionosphere characteristics with various indices of solar activity, and application of the theory of radio wave propagation.

rate.

IGY WORLD DATA CENTER A

The Data Center continues to receive IGC and post-IGC data at a high A special effort is underway to acquire and catalog all outstanding IGY data. During the year there was a notable increase in requests for data, most of the requests coming from scientific industry. Plans have been made to collect and exchange reprints and reports concerning Airglow and Ionosphere. This new service will aid scientists in the use of the materials available from the Data Center.

2.3.5. CRYOGENIC ENGINEERING

The Bureau's activities in cryogenic engineering, a rapidly growing specialized field, center at the Boulder Laboratories. The Bureau provides information needed for practical applications of materials, systems, and techniques at very low temperatures, and assists Government and industry with problems arising in this field.

Demand for assistance in projects involving cryogenics has increased greatly as a result of missile and space programs which rely on cryogenic liquids as propellants. The growth of cryogenic engineering has been accompanied by emphasis on purely scientific programs in which the use of extremely low temperatures can be an important aid. To cooperate in these activities, the laboratory conducts research on the physical properties of materials and properties of fluids, as well as on cryogenic processes and equipment. In addition, it maintains a national Cryogenic Data Center where information on cryogenic engineering is collected and organized for use by other Government agencies, industry, and the public.

Superconducting Electromagnets. High magnetic fields have important uses as deflectors of charged particles, as, for example, in the particle accelerators and detection devices of nuclear physics, in magnetohydrody namic power converters, and for plasma containment in nuclear fusion reactors. Substantial reduction of the power dissipated as heat in electromagnets can be achieved if the magnet conductor is cooled to low temperatures so as to greatly reduce its electrical resistance. Until recently, the further step of utilizing a superconductor was not regarded as practical, because most superconductors are driven into the normal state by rather small magnetic fields. However, in the past year several alloys and compounds have been found to remain superconducting in the presence of high fields and while carrying large currents. One of these, niobium-clad Nb3Sn, has been investigated by NBS, under Atomic Energy Commission sponsorship, in fields up to 190,000 gauss. The results indicate that solenoids can be made of this material that will produce fields of well over 100,000 gauss if operated at 1 to 4 °K. There is now intense activity in a number of laboratories on high-field superconductors.

Properties of para-Hydrogen. The specific impulse of a rocket propellant varies inversely with the square root of the masses of the ejected particles. Consequently the most advanced chemical and nuclear rocket schemes utilize hydrogen as a reactant and as a propellant fluid, respectively. Data concerning the thermodynamic and transport properties of hydrogen. must now be known with higher accuracy and over wider ranges of temperature and pressure than have been hitherto necessary. With the support of the Air Force and, more recently, the National Aeronautics and Space Administration, the Bureau has completed precise measurements of the pressurevolume-temperature characteristics of liquid and gaseous para-hydrogen from 20 to 100 °K and at pressures up to 350 atmospheres. Measurements of the specific heat are in progress. Detailed thermodynamic charts and tables will be prepared from these data.