Surface Pressure Observations Research Articles

Long‐period variations in the solar semidiurnal atmospheric tide

A 79‐year record (1866–1944) of hourly surface pressure observations at Batavia (6.2°S, 106.8°E) was analyzed to detect systematic long‐period variations in the solar semidiurnal barometric oscillation (S2(p)). Evidence was found for a quasi‐biennial oscillation (QBO) in S2(p) throughout the latter half of the record (1905–1944). This is attributed to the effect of the familiar QBO of the tropical stratospheric mean winds and temperatures on the solar semidiurnal tide. The results thus suggest that the stratospheric QBO itself has been proceeding in something like its present form since at least the beginning of the twentieth century. Some theoretical calculations were performed of the change expected in S2(p) between the minimum and maximum in the sunspot cycle by employing different published estimates of the solar ultraviolet flux variability. It is clear from the present S2(p) observations that, if there is any regular 11‐year cycle in the solar ultraviolet flux at wavelengths >200 nm, then it must be much smaller than some of the published estimates based on direct flux measurements. However, for periods around two individual sunspot minima (1867 and 1913) there are changes in the Batavia S2(p) consistent with a large drop in solar ultraviolet output.

Errors in atmospheric tidal determination from surface pressure observations

AbstractIt has previously been assumed that by taking a sufficient length of data the mean atmospheric tide at any tropical station could be determined to an accuracy of a few percentage points by using surface pressure observations. However, evidence is herein presented which shows that the inferred amplitude of the tide can be changed by over 20% just by changing the instrument used to measure atmospheric pressure. This has occurred both when one barometer has replaced another and when one barograph has replaced another at the same station. It is suggested that the main reason for the inaccuracy is that diurnal temperature variations cause systematic instrumental errors. There are important implications for the accuracy of all tidal determinations that have been made and for the reliability of tidal theory.

Errors in atmospheric tidal determination from surface pressure observations

Errors in atmospheric tidal determination from surface pressure observations

Statistical Properties of the Atmospheric Pressure Field Over the Arctic Ocean

Many useful statistical properties can be derived for isotropic, stationary, homogeneous, Gaussian random fields. The field of surface pressure in the region north of 70°N is shown to approximately satisfy these conditions. Under these conditions, all properties of the field are related to the autocovariance, which is a function of time and space lag. In particular, the following quantities are derived: the time and space covariance functions for the geostrophic wind; the covariance functions for the vorticity of the geostrophic wind; the average number of highs, lows and saddles per unit area; the average number of highs, lows and saddles at which the vorticity exceeds a specified threshold; and the probability density function for the Gaussian curvature of the pressure surface. The horizontal shear in the geostrophic wind is also investigated, as is the number of umbilic points per unit area. Estimates for all these quantities are constructed using observations of surface pressure from the Arctic Basin during 1979 and 1980. The comparison between theory and observation is favorable. At least when these several quantities are considered, the isotropic, stationary, homogeneous, Gaussian random process is a good model of the actual pressure field.

Global dynamic responses of the atmosphere to the eruption of Mount St. Helens on May 18, 1980

We present evidence that shows some aspects of the global atmospheric dynamic responses to the eruption of Mount St. Helens on May 18, 1980. Although events such as volcanic eruptions may excite a number of acoustic‐gravity wave modes in the atmosphere, the observed surface pressure perturbations and distant ionospheric perturbations can be explained only in terms of propagation of Lamb modes with a horizontal propagation velocity slightly above 300 m/s. Results from model computations show good agreements with the observational data. Ground level pressure perturbations created by this event are only slightly smaller than those created by the historical Great Siberian Meteor.

The Life Cycle of Thunderstorm Gust Fronts as Viewed with Doppler Radar and Rawinsonde Data

This paper presents the time-dependent analysis of the thunderstorm gust front with the use of Project NIMROD data. RHI cross sections of reflectivity and Doppler velocity are constructed to determine the entire vertical structure. The life cycle of the gust front is divided into four stages: (1) the formative stage; (2) the early mature stage; (3) the late mature stage; and (4) the dissipation stage. A new finding is a horizontal roll detected in the reflectivity pattern resulting from airflow that is deflected upward by the ground, while carrying some of the smaller precipitation ahead of the main echo core of the squall line. This feature is called a 'precipitation roll'. As determined from rawinsonde data, the cold air behind the gust front accounts for the observed surface pressure rise. Calculations confirm that the collision of two fluids produce a nonhydrostatic pressure at the leading edge of the outflow. The equation governing the propagation speed of a density current accurately predicts the movement of the gust front.

Variations in Tropical Sea Surface Temperature and Surface Wind Fields Associated with the Southern Oscillation/El Niño

Surface marine observations, satellite data, and station observations of surface pressure and precipitation are used to describe the evolution of sea surface temperature (SST) anomalies, surface wind fields, and precipitation anomaly patterns during major warm episodes in the eastern and central tropical Pacific. The sequence of events is described in terms of composite SST and wind fields (30°N–30°S) for six warm episodes since 1949, and time series and cross-spectral analyses of mean monthly data along six shipping lanes which cross the equator between the South American coast and 170°W. During the months preceding a warm episode, the equatorial easterlies are stronger than normal west of the dateline. This and other coherent and strongly developed anomaly patterns over the western equatorial Pacific and South Pacific are associated with a South Pacific Convergence Zone (SPCZ) located southwest of its normal position. During October-November prior to El Niño, the equatorial easterly anomalies in the western Pacific are replaced by westerly anomalies. This change coincides with the appearance of positive SST anomalies in the vicinity of the equator near the dateline. East of the dateline (140–170°W), the wind anomalies along the equator follow a different pattern, with the diminution of the easterlies lagging rather than leading the development of positive SST anomalies near the Ecuador-Peru coast. Further south, SST's increase and the easterlies show a general decrease over most of the latitude band 10–30°S prior to the coastal warming. Composites and cross-spectral analysis clearly show a westward migration of the eastern equatorial Pacific SST anomaly pattern from the South American coast into the central equatorial Pacific. Maximum SST anomalies typically occur around April-June along the South American coast, and near the end of the year around 170°W. This westward spread of positive SST anomalies coincides with the intensification of westerly wind anomalies along the equator and the development of anomalous northerly flow across the mean position of the lntertropical Convergence Zone (ITCZ). The southward shift of this convergence belt is accompanied by a northeastward shift of the SPCZ, resulting in a matter wedge-shaped dry zone and enhanced precipitation in the eastern and central tropical Pacific. The surface wind anomaly field in the central equatorial Pacific is most strongly developed during August-December following the maximum SST anomalies along the Ecuador-Peru coast. During the northern winter following El Niño, the positive SST anomalies, as well as the low-level convergence and positive precipitation anomalies, are concentrated in the central equatorial Pacific. A simple calculation based on the surface divergence composite indicates that at this time enhanced large-scale vapor flux convergence in this area is comparable in magnitude to the enhanced precipitation. The western end of a precipitation anomaly seesaw also appears in the data. Below normal precipitation is observed over Indonesia during the year of El Niño. Negative precipitation anomalies in the subtropics are associated with enhanced divergence and a weakened east Asian northeast winter monsoon in the Northern Hemisphere, and a weakened summer convergence zone east of Australia in the Southern Hemisphere.

Impact of FGGE Buoy Data on Southern Hemisphere Analyses1

Surface pressure observations from the First GARP Global Experiment (FGGE) drifting buoys, transmitted over the Global Telecommunication System, have been used in the Melbourne National Meteorological Analysis Centre (NMAC) operational analysis program since December 1978. From the beginning of the first Special Observing Period the network of buoys was sufficient to provide a data base over many areas from which routine surface observations have never previously been available. The great value of the new data in the specification of critical high latitude ridge axes, the true intensity of the Southern Ocean depressions and the westerly flow south of the Australian land mass is illustrated. It is shown that the 1979 analyses differ significantly from those of previous years, with regard to such features as the circumpolar trough, the middle latitude cyclonic systems and the sub-tropical highs. An appraisal of the differences indicates they are not only due to the characteristics of the 1979 circulation but also to a first delineation of the hemispheric circulation features by use of the FGGE data base.

On the use of a time sequence of surface pressures in four-dimensional data assimilation

The possibility of using a time sequence of surface pressure observations in four-dimensional data assimilation is being investigated. It is shown that a linear multilevel quasi-geostrophic model can be updated successfully with surface data alone, provided the number of time levels are at least as many as the number of vertical levels. It is further demonstrated that current statistical analysis procedures are very inefficient to assimilate surface observations, and it is shown by numerical experiments that the vertical interpolation must be carried out using the structure of the most dominating baroclinic mode in order to obtain a satisfactory updating. Different possible ways towards finding a practical solution are being discussed. DOI: 10.1111/j.2153-3490.1980.tb00946.x

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.

Experimental Investigation of Hypersonic Buzz on a Delta Configuration

N experimental study is described which confirms the existence of hypersonic buzz in the separated region of a downward deflected control surface. Wind-tunnel tests in helium at M = 17.5 clearly demonstrated the occurrence of large-scale pressure oscillations throughout a substantial range of angles of attack and control surface deflections on a blunt slab, delta configuration. Measurements of surface pressure fluctuations and observations of high-speed schlieren photographs served to delineate the boundaries of the phenomenon and to identify the physical parameters necessary for the onset of a buzz condition. Prominent spectral energy peaks in surface pressures were observed and correlated with the instability. These conditions were found to be strongly dependent on the presence of multiple shock interactions relative to the location of a reattaching shear layer.

Surface properties and hysteresis of dipalmitoyllecithin in relation to the alveolar lining layer

1. 1. Investigations using surface pressure and surface potential measurements and observations of changes in the film state were undertaken to account for the factors which determine the surface properties and hysteresis of l-α-dipalmitoyllecithin films which have been reported to resemble lung extract films and to be mainly responsible for the capacity of the alveolar lining to maintain lung stability. 2. 2. When a film of l-α-dipalmitoyllecithin is compressed intermittently to an area short of film collapse, hysteresis increases with the extent of film compression and it is associated with parallel changes in surface pressure and surface potential and is reproducible in successive cycles. Lecithin films are in the liquid state below surface pressure of 35 dynes/cm, in the gel state between 35 and 40 dynes/cm and in the solid state above 40 dynes/cm. 3. 3. When compression is continued beyond film collapse (about 44 dynes/cm) surface pressure rises sharply unaccompanied by a parallel increase in surface potential. Here hysteresis results from film solidification and loss of material from the surface and probable entrance of saline solution into gaps in the film during expansion. 4. 4. Initially highly compressed lecithin films formed by adding large quantities to the surface exhibit an earlier onset of film solidification, and of displacement of material from the surface during compression, and therefore, a greater degree of hysteresis, than initially fully expanded films. 5. 5. If the alveolar lining layer responds to compression and expansion during respiration as a l-α-dipalmitoyllecithin film responds in a film balance, then it is stable during expiration only when surface tension is above 32−28 dynes/cm. Below this surface tension level, the lining layer would collapse and the material displaced would have to return to the alveolar surface or be replenished during inspiration to maintain a healthy alveolar lining layer. The studies reported herein indicate that lecithin displaced from the surface during compression is not restored during expansion.

SURFACE PRESSURE VARIATIONS AT COASTAL STATIONS DURING THE PERIOD OF IRREGULAR MOTION OF HURRICANE CARLA OF 1961

Abstract Surface pressure observations at stations along the Texas coast during the approach of hurricane Carla of 1961 have been examined in an attempt to determine the extent to which the storm as a whole participated in the irregular motion indicated by the track of the storm center as followed by radar. The pressure variations at coastal stations were found, in general, to correlate rather poorly with changes in the direction and speed of motion of the storm center. The best agreement was shown by the Galveston observations which were made some 100–150 mi. to the right of the storm track.

The distribution of the semidiurnal pressure oscillation on the Antarctic continent

Two years of three-hourly surface pressure observations from six stations, established on the Antarctic continent during the International Geophysical Year, were subjected to harmonic analysis to determine the phase and amplitude of the 24-hour and the 12-hour pressure oscillations. An analysis of variance indicated that both the 24- and 12-hour components of the daily pressure wave were present. On the average, the amplitude of the semidiurnal pressure variation for the Antarctic stations during this period was about one-half the value previously found in the Arctic. An interesting feature is the apparent existence of the diurnal pressure oscillation at the geographical south pole (Amundsen-Scott station).

Neutral molecules and a simplified treatment for ions

Films of neutral substances adsorbed at the oil/water interface obey the equation of state and the adsorption isotherm which are derived assuming complete mobility of the molecules in the interface. The equations are obeyed down to areas of ~ 30A 2 per molecule; deviations which occur below this value result from interactions between the adsorbed molecules. Adsorbed films of completely ionized sodium alkyl sulphates and quaternary am m onium compounds also obey these equations when allowance is m ade for the electrical contribution to the adsorption energy and for electrical interaction between the ions in the aqueous bulk phase. The activity coefficients cannot be neglected in these systems at concentrations exceeding 0.001 m. In the range 0.001 to 0.09m the ‘complete’ Debye-Huckel equation is used to calculate these coefficients; at the higher concentrations (for sodium decyl and octyl sulphates) the activity coefficients thus calculated are suspect. The electrical energy is given exactly by a modified Gouy equation, when allowance is made for the film ions being situated a finite equilibrium distance from the interface and for the fact that counter-ions will be present above the head groups. This modified equation yields linear plots for the isotherm and leads to consistent values for the free energy of adsorption of the molecules. It also ( a ) demonstrates th at the electrical potential at the phase boundary (jrd) differs from that in the plane for the film ions (i/r0) and th at the true jr0 is lower than th at calculated from the simple Gouy equation; from the m easured surface potentials (AF) interpreted by the equation of Schulm an & Hughes (1932), it is shown th at the calculated is experim entally confirmed; ( b ) predicts much more accurately than the simple equation the relation between the observed surface pressure (17) and area per molecule (equation of state). Deviations from the equations occur for short-chain compounds (C8 and C 10) in w ater at high concentrations, and for all surface-active agents in high electrolyte concentrations (> m/100), especially where A < 70A 2 . It is concluded that these deviations result m ainly from a neglect of ionic size in the theoretical treatm ent. There is no evidence in any of the systems for any specific interaction between counter ions and adsorbed film ions. The experimental results are inconsistent with the view that appreciable energy changes associated with dehydration of the surface-active ions occur as they approach the oil/water interface.