Surface Pressure Variations Research Articles

Simulation of Atmospheric Variability

A spectral atmospheric circulation model is time-integrated for approximately 18 years. The model has a global computational domain and realistic geography and topography. The model undergoes an annual cycle as daily values of seasonally varying insolation and sea surface temperature are prescribed without any interannual variation. It has a relatively low computational resolution with 15 spectral components retained in both zonal and meridional directions. Analysis of the results from the last 15 years of the time integration indicates that, in middle and high latitudes, the model approximately reproduces the observed geographical distribution of the variability (i.e., standard deviation) of daily, monthly and yearly mean surface pressure and temperature. In the tropics, the model tends to underestimate the variability of surface pressure, particularly at longer time scales. This result suggests the importance of processes with long time scales such as ocean–atmosphere interaction, in maintaining the variability of the atmosphere in low latitudes. It is shown that global mean values of standard deviation of daily, 5-daily, 10-daily, monthly, seasonal and annual mean surface pressure of the model atmosphere may be approximately fitted by a corresponding set of standard deviations of a red noise time series with a decay time scale of slightly longer than four days. However, it appears that the temporal variation of surface pressure also includes minor contributions from disturbances with much loner decay time scales. In general, the model tends to underestimate the persistence (or decay time scale) of atmospheric disturbances. However, it reproduces some of the features of the observed geographical distribution of decay time scale of the surface pressure fluctuations in middle and high latitudes. The observed standard deviation of annual, hemispheric mean surface air temperature also is compared with model results. Although a clearcut evaluation of model performance is somewhat hampered by observational uncertainty, it appears that the model's value amounts to a substantial fraction of the corresponding standard deviation derived from observational studies.

Interdiurnal Surface Pressure Variations in Brazil: Their Spatial Distributions, Origins and Effects

Abstract A study is made of the spatial correlation of interdiurnal surface pressure variations in Brazil. Pressure oscillations that occur in southern Brazil, associated with midlatitude synoptic systems, are shown to be positively correlated with pressure oscillations near the equator. The correlation maxima show an eastward displacement with increasing lag. Interannual variability in the correlation coefficients is discussed and related to variability in the intensity and frequency of midlatitude systems, which affect the region. Some Southern Hemisphere synoptic systems have a marked effect on convective activity over the Amazon Basin, with the area of maximum activity showing an eastward displacement with time. A principal component analysis reveals that only the patterns of the first four eigenvectors have readily identifiable causes. These are associated with large-scale features, such as planetary waves and blocking, and typical wintertime, summertime and springtime patterns. The corresponding eig...

Calculation of Unsteady Transonic Flow over an Airfoil

An implicit finite-difference solver for either the Euler equations or the thin-layer Navier-Stokes equations was used to calculate a transonic flow over the NACA 64A010 airfoil pitching about its one-quarter chord. An unsteady automatic grid-generation procedure that will improve significantly the computational efficiency of various unsteady flow problems is described. The calculated results for both inviscid and viscous flows at Mach number 0.8 over the airfoil oscillating with reduced frequency referenced to one-half chord, 0.2, are compared with experimental data measured in the Ames 11 x 11 ft Transonic Wind Tunnel. Nonlinear, unsteady effects of the flow on the surface pressure variations, shock-wave excursions, and overall airloads are examined. Good agreements between the results of computations and experiments were obtained. In the shock-wave region, however, the results of the viscous-flow computations showed closer agreement with the experimental data.

Surface Pressure Response to Elevated Tidal Heating Sources: Comparison of Earth and Mars

Modern atmospheric tidal theory has shown that the dominance of the terrestrial semidiurnal surface pressure oscillation, relative to its diurnal counterpart, is the result of the elevated heating source generated by solar heating of stratospheric ozone. Observations of the daily surface pressure variation at the Viking Lander 1 site on Mars reveal a similar predominance of the semidiurnal surface pressure oscillation only during the onset of a Martian great dust storm. Application of a classical, analytic tidal model to the Viking Lander 1 data indicates that elevating the effective heat source due to solar heating of airborne dust by a few kilometers during the onset of a Martian great dust storm can account for the observed semidiurnal surface pressure variation.

Correlation of high latitude tropospheric pressure with the structure of the interplanetary magnetic field

In the past decade there has developed a body of circumstantial evidence suggesting that terrestrial meteorology is influenced by plasma and magnetic field properties of the solar wind. In this paper we shall present evidence which strongly suggests that variations in surface pressure at high latitude stations ringing the Gulf of Alaska are correlated with changes in direction of the interplanetary magnetic field. We shall also present evidence that the changes in surface pressure may depend on whether the interplanetary magnetic field changes from pointing sunward to pointing antisunward or vice versa. We shall discuss the role that the magnetospheric electric field, which is heavily modulated by the interplanetary magnetic field, may play in influencing processes which lead to changes in terrestrial weather patterns.

Thermal tides and Martian dust storms: Direct evidence for coupling

Observations of surface pressure oscillations at the Viking 1 and Viking 2 lander sites on Mars indicate that the thermally driven global atmospheric tides were closely coupled to the dust content of the Martian atmosphere, especially during northern fall and winter, when two successive global dust storms occurred. The onset of each of these global storms was marked by substantial, nearly simultaneous increases in the dust opacity and in the range of the daily surface pressure variation observed at both lander sites. Although both the diurnal and semidiurnal tidal surface pressure components were amplified at Lander 1 during the onset of a global dust storm, the semidiurnal component was greatly enhanced in relation to the diurnal tide. Semidiurnal wind components were prominent at both lander sites during the height of the global dust storm. We have attempted to interpret these observations using simplified dynamical models. In particular, the semidiurnal wind component can be successfully related to the observed surface pressure variation using a simplified model of a semidiurnally forced Ekman boundary layer. On the other hand, a classical atmospheric tidal model shows that the preferential enhancement of the semidiurnal surface pressure oscillation at Lander 1 can be produced by a tidal heating distribution which places most of the heating (per unit mass) above 10‐km altitude. Furthermore, when a dust storm expands to global scale, it does so rather quickly, and the total atmospheric heating at the peak of the dust storm can represent more than 50% of the available insolation. The Viking observations suggest that a number of mechanisms are important for the generation and decay of these episodic Martian global dust storms.

Meteorological forcing of coastal waters by the inverse barometer effect

Water level and surface pressure data from the northeastern and northwestern Gulf of Mexico are used to investigate the water level response to meteorological forcing by the inverse barometer effect. Statistically significant coherence-squared values are computed for variations in cross-Gulf surface pressure and water level differences over time scales on the order of 2 to 6 days. Water level variations of approximately ±4–5 cm are postulated for the northern Gulf of Mexico in response to surface pressure differences. Meteorological forcing by the inverse barometer effect appears to be significantly greater in the winter months, when cross-Gulf air pressure differences of up to ±20 mb are recorded.

A theoretical study of phase transitions in bidimensional monolayers

We propose a theoretical study of phase transitions in long hydrocarbon chain monolayers, lying on aqueous substrate. We use a model taken from that applied by Di Marzio to liquid crystals: each molecule can occupy several aligned sites on the holder (1 to 5 for us). We also take into account the attractive interactions between the hydrocarbon chains in the framework of a mean field approximation: it gives a first order phase transition in a diagram showing surface pressure variations in terms of the molecular density, noted (π, ρ) diagram. We also introduce an order–disorder transition and we show that it is either of the first order, or of the second order, according to the physical conditions. The (π, ρ) isotherms are in good qualitative agreement with experimental results.

Some Characteristics of High Waves in Closed Channels Approaching Kelvin-Helmholtz Instability

The characteristics of water waves produced by flowing air in closed channels were studied to uncover the effects of surface pressure variation. From theoretical considerations, it is proposed that the point of onset of the Kelvin-Helmholtz instability for such waves may be found from 1.35ρaρwVc2ghc=1 Photographs of internal flow patterns and wave shapes confirm the occurrence of this instability, but the theoretically predicted reduction in wave celerity does not occur. The wave celerity for high waves was found to be predictable by the formula C=0.191gLtanh2πhwL1/2 The measured height to length ratios for the highest observed waves are of the order of 0.1.

Analysis of the Internal Gravity Wave Occurrence of 19 April 1970 in the Midwest

An analysis is made of high frequency, fluctuations of surface pressure and wind with a period of 3–4 h observed in the midwestern United States in the early morning hours of 19 April 1470. The phenomenon is shown to be of subsynoptic scale and clear interrelationships are established between the surface pressure, wind, and cloudiness variations. Solutions from a simple model of atmospheric dynamics for a compressible and hydrostatic flow are compared with the observations. It is shown that the fluctuations in the atmosphere correspond well to simple gravity wave concepts and in particular to internal gravity waves propagating to the northeast with an approximate speed of 50 m/s and an average wavelength of 500 km.

A synoptic climatology of satellite observed cloud vortices over the Southern Hemisphere

AbstractA classification scheme for satellite observed cloud vortices is used to assess some general features of the behaviour of Southern Hemisphere depressions. From coincident conventional observations the mean variation of surface pressure and upper level geopotential anomaly near the centre of, and in west‐east cross‐section through an extratropical vortex is determined in relation to its age. Data are obtained on the geographical variation of occurrence of vortex type, duration, and frequency of change between development stages. The percentage of vortices developing without a pre‐existing cloud band is found to be greater at higher latitudes but, in general, over 50 per cent of developments occur in this way.Persistent maxima of early vortex development are found in the western South Atlantic and in the central South Pacific, both regions extending into lower latitudes than elsewhere in the hemisphere. Two less prominent maxima are located in the central Indian Ocean, and south of Australia. Generalized vortex track and speed data are obtained, and several areas of high frequency of termination of depression track are observed at high latitudes near the Antarctic coast.In total, the observations tend to point to a circulation pattern having a high frequency of major long wave troughs east of the Andes, and in the central Pacific, with a further frequent trough more variable in space and time being located between the central Indian Ocean and the longitude of the Great Australian Bight.

A note on the diurnal variation of surface temperature and pressure at some Nigerian meteorological stations

Analysis of the diurnal pressure and temperature variations near the surface, shows that the pressure variation is caused by the heat energy absorbed both near the surface and at an upper level. In the case of the eight hourly oscillation, the effects of these two sources of energy are in antiphase and in August and March, each tends to annual the effect of the other.

Mariner 6 and 7 ultraviolet spectrometer experiment: Photometry and topography of mars

From data obtained by the ultraviolet spectrometers aboard the Mariner 6 and 7 Mars missions the reflectivity of the illuminated disk of Mars was found to have two distinct spectral types, associated with polar and nonpolar regions. In this work the characteristic spectrum of nonpolar regions on Mars is discussed. An interpretation of the variation of the intensity at 3050Å due to surface pressure variations is goven. A comparison of the ultraviolet observations with pressures inferred by the infrared spectrometer is used to test this interpretation and to determine physical parameters of Mars which lead to the observed reflectance. Earth based pressures obtained by broadening of the 1 μ band of CO 2 and radar topography are compared with the ultraviolet results.

Severe magnetic storms and surface pressure variations

Association of surface pressure variation with magnetic activity is studied, using the superposed epoch method. A steady fall in pressure upto about 4 days prior to the day of onset of severe magnetic storm is noticed.

Surface Pressure Variations in Polar Regions

Power and cross-power spectra involving the daily average station pressure at arctic and antarctic stations along with various measures of solar variability, such as fmin, riometer data, and Kp, failed to reveal any associations between solar particle emission and the surface pressure in polar legions. However, a small but apparently real, coherent variation in surface pressure exists between the two polar regions. This oscillation with period somewhat greater than 60 days is almost exactly 180° out of phase between the two polar regions, indicating a more or less direct exchange of mass between the arctic and antarctic.

QUASI-BIENNIAL VARIATIONS IN THE “CENTERS OF ACTION”

Abstract Quasi-biennial (about 28-mo) variations in surface pressure occur in the vicinity of the North Atlantic and North Pacific subtropical Highs and subpolar Lows, with harmonic amplitudes of order 0.4 mb. The subtropical Highs undergo quasi-biennial latitudinal and longitudinal oscillations averaging about 1° of latitude, with the Atlantic High apparently oscillating in the northeast-southwest direction and the Pacific High in the northwest-Southeast direction. The quasi-biennial pressure oscillations in the North Atlantic subpolar Low and subtropical High are almost out of phase, implying a relatively strong quasi-biennial variation in surface zonal wind in North Atlantic temperate latitudes. There is evidence for a quasi-biennial variation in frequency of hurricanes and typhoons in the North Atlantic and North Pacific, and of severe storms in the vicinity of India. Within the quasi-biennial framework, an above-average frequency of hurricanes or typhoons is associated with above-average pressure in ...

Tropical cloudiness and rainfall related to pressure and tidal variations

AbstractA definitive statistical relationship is established between tropical cloudiness and rainfall and the semidiurnal solar (S2) atmospheric tide, as manifested in the semi‐diurnal surface pressure variation. Pressure and weather data are used from Batavia (seventy years) and Wake Island (twelve years). TheS2tidal effect is shown to enhance cloudiness and rain near sunrise and sunset, and to suppress them shortly after midday and midnight. The analysis is based on (a) the fact that theS2amplitude varies by 15–20 per cent between months and by more than 100 per cent from day to day and (b) the amplitude of theS2wave as computed from the pressure data at a station is closely related to the 5–6 hourly pressure changes during the periods around 4–5 a.m. to 10 a.m., from 10 a.m. to 4 p.m., etc. The crux of the analysis is the demonstration that days with large 5–6 hourly pressure changes during these periods have large cloudiness changes (in the sense described above) during these same periods relative to days with small 5–6 hourly pressure changes.Possible mechanistic connections betweenS2pressure tendencies and cloud properties are examined. The varying convergence‐divergence field is suggested as the main link. It is shown how the concentration of active cloud updraughts in the Tropics can permit cloudiness to be extremely sensitive to small divergence fields.Finally, large‐scale simultaneous pressure changes over the Pacific Ocean area are shown and related to cloudiness changes. A need for re‐examination of the nature and origins of tropical disturbances is shown to exist, using the concept that possible small (terrestrial or extra‐terrestrial) triggers may set off significant changes in weather both locally and on the synoptic and global scales.

AN INVESTIGATION OF THERMAL TIDAL OSCILLATIONS IN THE EARTH'S ATMOSPHERE USING A GENERAL CIRCULATION MODEL

An investigation of tidal oscillations in the earth's atmosphere has been made using an 18 vertical level, hemispheric general circulation model. This approach permitted these tides to be investigated without resorting to linearization of the governing differential equations, as is required by the conventional approach. In addition, it allows the tides to be studied in relation to a realistic atmosphere, and thus in their actual roles as small perturbations, at least in the lower atmosphere, on the basic meteorological fields. Day-to-day surface pressure variations in good agreement with observation were produced by the model, the diurnal and semidiurnal pressure amplitudes and phases also being close to the observed values. An investigation into the excitation mechanism of the oscillation gave results supporting previous work in attributing the dominant cause of the tides to absorption of solar radiation by water vapor and ozone in the atmosphere. Contrary to previous studies, water vapor was found to be of primary importance in exciting both the diurnal and semidiurnal oscillations in the model atmosphere. Generally speaking, the tidal wind and temperature variations obtained were also in agreement with observation and other theoretical work.

The adsorption of toluene vapor on water surfaces

The adsorption of toluene vapor on a water surface has been studied using a sensitive film balance to obtain the variation of surface pressure with partial pressure of hydrocarbon vapor. Particular attention was paid to obtaining reliable data in the region of low surface pressure. The amount adsorbed on the surface was calculated using the Gibbs adsorption equation. Studies at six temperatures have allowed the thermodynamic quantities for the adsorption process to be calculated. The equilibrium heats and isosteric heats of adsorption decreased with coverage at low coverages suggesting that in the initial stages of adsorption changes in the structure of the water surface occurred as a consequence of the incorporation of a hydrocarbon molecule. In the region close to the saturation vapor pressure lenses of the organic phase were formed on the surface.

The application of monolayer techniques to a study of protein-surfactant interaction: II. Interactions in adsorbed films at the air/water interface and in oil-in-water emulsions

The effect of surfactants on monolayer properties (surface pressure, potential, viscosity, and elasticity) of adsorbed films of various proteins has been studied. Bovine serum albumin was used to determine the changes in these surface parameters which occur with variation of bulk pH, surfactant charge, and initial surfactant surface pressure. These measurements were extended to include the interactions of other proteins (hemoglobin, cytochrome c, ovalbumin, β-lactoglobulin, γ-globulin) on each side of their respective isoelectric points with the cationic surfactant n-docosyl trimethylammonium bromide. In general the behavior showed good agreement with that observed in Part I for spread films, and in particular large reductions in surface viscosity and elasticity were recorded in the presence of surfactant. Supporting measurements are included on protein-stabilized emulsions; these were found to exhibit decreased stability in the presence of surfactants. This was attributed to the change in mechanical properties of the adsorbed films and the possible significance of the observed effects in systems of technical and biological interest is outlined.