Deg Latitude Research Articles

Solar Semidiurnal Tide in the Thermosphere

The behavior of the solar semidiurnal tide in the thermosphere is studied on the basis of a three-dimensional model involving viscosity, thermal conductivity, Coriolis effects, sphericity of the earth, and ion drag. Sources of excitation are absorption of solar radiation by H2O and O3 below the mesopause, and by O2 in the Schumann-Runge continuum (SRC), and O, O2, N2 in the extreme ultraviolet (EUV), in the thermosphere. The relative importance of EUV, SRC, and forcing below the thermosphere are assessed. The semidiurnal tide in the lower thermosphere is re-examined, and the utility of equivalent gravity mode calculations is evaluated. The calculations presented provide detailed predictions for all meteorological fields as functions of season, solar cycle, and other parameters. In particular, the semidiurnal tide between 100 and 130 km is dominated by the 2,4 mode excited below the thermosphere. During sunspot minimum, forcing from below is dominant, but during sunspot maximum tides from below are so severely attenuated within the thermosphere that thermospheric in situ forcing becomes relatively more important. Results are compared with tidal observations at 45 deg latitude.

Short-Range Forecasts with the GISS Model of the Global Atmosphere

Results of tests carried out during the period from December 1972 through January 1973 to determine the short-term forecasting accuracy of a multilevel numerical primitive-equation (PE) model of the global atmosphere developed at the Goddard Institute for Space Studies (GISS). Six 48-hr forecasts were carried out with the aid of this model, using nine vertical levels and a horizontal grid spacing of 4 deg in latitude and 5 deg in longitude for an effective grid point separation averaging slightly more than 400 km. Verification of forecast sea-level pressures, 1000-mb heights, and 500-mb heights, as well as 1000-mb and 500-mb vector geostrophic winds, shows that the model has forecast skill comparable to that of operational PE models. Based on the 36-hr evolution of 18 extratropical cyclones, the model forecasts exhibit a tendency toward underestimating their propagation speeds and overestimating their central pressures. Both deficiencies are attributed to inadequate horizontal grid resolution. Quantitative verification of forecast surface temperatures over the eastern United States shows a forecast skill equal to that achieved by combined dynamical-statistical procedures.

Behavior of the ionosphericFregion during the Great Solar Flare of August 7, 1972

The response of the ionospheric F region to the large solar flare that occurred near 1500 UT on August 7, 1972, has been monitored by means of Faraday rotation measurements made at 17 stations in North America, Europe, and Africa. With observations spanning more than 10 hours in local time and more than 70 deg in latitude, the first truly global morphology of a flare-induced F region event was obtained. The sizes of the individual sudden increases in the total electron content (Sitec) ranged from 1.8 to 8.6 × 1016 el/m²; on a percentage basis, all the Sitec fell within the 15 to 30% range. No obvious relationship was found between the sizes of the increases and the solar zenith angles at the various subionospheric points, nor between the observed Sitec and the sudden flare effects (SFE) seen on nearby magnetometer recordings. The latitudinal behavior provided the only simple ordering parameter found in the data, the lower latitudes having larger observed increases than the higher latitudes. Millstone Hill incoherent scatter data showed that nearly 40% of the total content enhancement observed at that site came from heights above 300 km. All the Sitec had a rise time of about 10 min, during which the Tec rate of change showed an excellent correlation with the time development of the solar radio burst monitored at 35,000 MHz.

Preliminary albedo map of the south polar region

A preliminary albedo map of the Martian south polar region in stereographic projection was prepared mainly from mission test video system (MTVS) prints before rectified and gridded prints were received, but some adjustments were made to conform with a semi-controlled photomosaic. Wherever possible, use also was made of crater coordinates. Two versions of the map are presented: one with a coordinate grid overlay and one without it. The precision of the coordinates is generally within 1 deg in latitude and the corresponding are in longitude. The maps show both the albedo markings and, with subdued contrast, the craters and topographic features that are necessary to locate the former. The map covers the range of latitudes from - 65 deg to the south pole.

Mars atmosphere during the Mariner 9 extended mission: Television results

The Extended Mission of Mariner 9 provided data from 23 revolutions and recorded seasonal changes in the atmosphere of Mars during northern spring and early summer. The visibility of the surface was exceptional, indicating atmospheric clarity greater than that previously observed by Mariner 9 or by Mariner 6 and 7. Cloud systems were observed over both polar regions and indicated westerly winds in the -45 to -65 deg latitude zone (southern winter) and easterly winds in the vicinity of +75 deg (northern summer). The puzzling brightening phenomena that recur seasonally and diurnally over Tharsis, Amazonis, and Nix Olympica were seen to be clouds of a generally diffuse character but with some indications of convective activity. These clouds show a remarkable degree of topographic control, and their large-scale patterns are closely duplicated from day to day.

Observations of Spatial Structure in the Soft X-Ray Diffuse Flux

Repeated observations of a diffuse source in the region of about 200 deg and +10 deg galactic longitude and latitude, respectively, illustrate the complexity of the low-energy X-ray background. The source is not well correlated with known objects or features, and cannot be explained by geometrically simple models of diffuse emission. The measurements indicate that this emission feature, and by implication a large fraction of the 1/4-keV flux observed in the galactic plane, probably originates outside the solar system.

Quasi-Biennial Oscillation in Ozone

Abstract Harmonic analyses of mean monthly ozone data, after the annual cycle has been removed, have shown the existence of the quasi-biennial oscillation with a period of about 26 months. It extends from the equator to the temperate and polar latitudes in the Northern Hemisphere. In the Southern Hemisphere its existence is confirmed at Aspendale and Brisbane. The amplitude of the 26-month oscillation in ozone follows a meridionalwave pattern with an approximate wavelength of about 30 deg of latitude. The oscillation at the position of the tropical amplitude maximum is approximately out of phase with the oscillation at temperate and polar latitudes, the latter two being in phase with each other. The 26-month oscillation in ozone is nearly in phase with the corresponding oscillation in temperature at about 55 mb.

Numerical Studies of Seasonal and Latitudinal Variability in a Model Thermosphere

Abstract A numerical model of the diurnal pattern of heating and subsequent structural changes in the thermosphere has been used to investigate the seasonal and latitudinal variability of neutral atmospheric properties in that region. The model calculations indicate the requirement for poleward energy transport in middle and high latitudes at equinox and at all latitudes in the winter hemisphere at solstice. Maximum temperatures in the summer hemisphere at solstice occur at about 45 deg latitude. No explicit horizontal variability is permitted in the present model, and a comparison of the model results with the data available from satellite drag observations indicates that horizontal motions must be important in the determination of the phase and amplitude of the diurnal temperature oscillation and of the temperature structure at high latitudes during winter.

The 26-Month Oscillation in Zonal Wind and Temperature

Abstract Harmonic analysis of mean monthly zonal wind and temperature data,after removing the annual cycle, have shown the existence of the 26-month oscillation in the equatorial stratosphere. The oscillation in temperature extends to temperate and polar latitudes, while in zonal wind it is insignificant beyond 25N. The amplitude of the 26-month oscillation in temperature follows a meridional wave pattern with an approximate wavelength of about 30 deg of latitude. The phase of the 26-month oscillation in both zonal wind and temperature progresses downward, at equatorial latitudes, with a speed a little less than 1 km per month. The oscillation in temperature at the position of the tropical amplitude maximum is approximately out of phase with the oscillations at high level equatorial latitudes and at temperate and polar latitudes.

Negative correlation between polar-cap visual aurora and magnetic activity

The relationship between the local (K) and planetary (K/sup p/ magnetic activity and the occurrence of visual auroras inside the auroral zone is investigated. The visual aurora above geomagnetic latitude 80 deg is found to be negatively correlated with the K and K/sub p/ magnetic indexes, whereas nearer to the auroral zone the correlation is positive. The relationship in the region 75 to 80 deg latitude is more complicated and has a transitional nature. (auth)

Stability of Jets in a Divergent Barotropic Fluid

The stability of a two-layer incompressible fluid system on a rotating earth is investigated. The upper layer has infinite depth and is inert; the lower layer has finite depth and a basic west to east zonal velocity of form sech2y. The linearized potential vorticity equation is used for the stability investigation. It is found that both the beta effect due to the curvature of the earth and the divergence tend to stabilize the jet if the winds are from west to cast everywhere. However, if there are easterly winds away from the center of the jet, the divergence may not be stabilizing. This stability theory is applied to a jet at 45 deg latitude in the atmosphere. The maximum wind is 60 m sec1 and the half-width of the jet is 1000 km. For the case of no divergence the most unstable wavelength is 5500 km and this disturbance has an e-fold amplification in 1.8 days. If we include divergence, the most unstable wavelength is again 5500 km but the e-fold amplification time is 14 days. The theory can also be applied to the Gulf Stream. For a current with a maximum velocity of 1.5 m sec−1, a half-width of 31 km and a depth of 550 m, the most unstable wavelength is 180 km and the e-fold amplification time is 4 days.

Application of a Moving-Coordinate Prediction Model to East Coast Cyclones

A statistically derived procedure for forecasting the 24-hr displacement. change in central pressure, and change in intensity of east coast cyclones is presented. The analysis is based on a moving coordinate system—i.e., predictor information is measured at points fixed with respect to the moving cyclone center rather than at points fixed with respect to the earth. Two sets of multiple linear regression prediction equations are derived from a sample of 352 cyclone cases. The first set is based solely on point values of sea-level pressure, 500-mb height, 1000–500-mb thickness, and 12-hr changes of these variables. The second set is based on point values plus a series of quantities derived from point values such as steering components, gradients, vorticity and thickness advection, and thermal wind. When applied to 106 independent cases, the point value equation yield a vector position root-mean-square (rms) error of 4.01 deg of latitude and a central pressure rms error of 8.70 mb. The complex equations fail to improve these scores significantly. Operational 24-hr forecasts made for 31 cases during the winter of 1959–1960 are compared with corresponding 18-hr forecasts prepared by the National Weather Analysis Center (NWAC). The statistical forecasts incur a vector rms error of 2.25 deg of latitude for position and a rms error of 8.14 mb for deepening; NWAC forecasts incur a rms error of 3.87 deg of latitude and a rms error of 7.25 mb for deepening.

Concentration du radon et du thoron dans l'air, au dessus de lOcéan Atlantique. Equilibre radioactif entre ces gaz et leurs descendants

Measurements of the concentration of Rn and Tn were made from May 28 to June 28, 1962, aboard the meteorologicai ship France II, anchored at 45 deg latitude N and 16 deg longitude E. The concentrations of the radioactive decay products of Rn and Tn were measured at the same time to study the radioactive equilibrium between Rn and its descendants in the air above the Atlantic Ocean and to determine the variation of the concentrations as a function of the meteorological conditions. The sampling technique is described. The Tn activity and the ThB and ThC activities remained below 5.5 x 10/sup -15/ C/l of air. The radioactive equilibrium of Rn and its descendants remained constant at 5.3, dependent of the wind velocity. The concentration of Rn, however, seemed to be quite dependent on meteorological factors.