An upgraded version of the Hadley Centre’s monthly historical mean sea level pressure (MSLP) dataset (HadSLP2) is presented. HadSLP2 covers the period from 1850 to date, and is based on numerous terrestrial and marine data compilations. Each terrestrial pressure series used in HadSLP2 underwent a series of quality control tests, and erroneous or suspect values were either corrected, where possible, or removed. Marine observations from the International Comprehensive Ocean Atmosphere Data Set were quality controlled (assessed against climatology and near neighbors) and then gridded. The final gridded form of HadSLP2 was created by blending together the processed terrestrial and gridded marine MSLP data. MSLP fields were made spatially complete using reduced-space optimal interpolation. Gridpoint error estimates were also produced. HadSLP2 was found to have generally stronger subtropical anticyclones and higher-latitude features across the Northern Hemisphere than an earlier product (HadSLP1). Duri...

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A new globally complete monthly historical gridded mean sea level pressure dataset (HadSLP2): 1850-2004

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There are at least three independent ways in which the solar wind modulates the flow of current density (Jz) in the global electric circuit. These are (A) changes in the galactic cosmic ray energy spectrum, (B) changes in the precipitation of relativistic electrons from the magnetosphere, and (C) changes in the ionospheric potential distribution in the polar caps due to magnetosphere-ionosphere coupling. The current density J
z flows between the ionosphere and the surface, and as it passes through conductivity gradients it generates space charge concentrations dependent on J
z and the conductivity gradient. The gradients are large at the surfaces of clouds and space charge concentrations of order 1000 to 10,000 elementary charges per cm3 can be generated at cloud tops. The charge transfers to droplets, many of which are evaporating at the cloud-clear air interface. The charge remains on the residual evaporation nuclei with a lifetime against leakage of order 1000 sec, and for a longer period the nuclei also retain coatings of sulfate and organic compounds adsorbed by the droplet while in the cloud. The charged evaporation nuclei become well mixed with more droplets in many types of clouds with penetrative mixing. The processes of entrainment and evaporation are also efficient for these clouds. The collection of such nuclei by nearby droplets is greatly increased by the electrical attraction between the charge on the particle and the image charge that it creates on the droplet. This process is called electroscavenging. Because the charge on the evaporation nuclei is derived from the original space charge, it depends on J
z, giving a rate of electroscavenging responsive to the solar wind inputs. There may be a number of ways in which the electroscavenging has consequences for weather and climate. One possibility is enhanced production of ice. The charged evaporation nuclei have been found to be good ice forming nuclei because of their coatings, and so in supercooled clouds droplet freezing can occur by contact ice nucleation, as the evaporation nuclei are electroscavenged. Although quantitative models for the all the cloud microphysical processes that may be involved have not yet been produced, we show that for many clouds, especially those with broad droplet size distributions, relatively high droplet concentrations, and cloud top temperatures just below freezing, this process is likely to dominate over other primary ice nucleation processes. In these cases there are likely to be effects on cloud albedo and rates of sedimentation of ice, and these will depend on J
z. For an increase in ice production in thin clouds such as altocumulus or stratocumulus the main effect is a decrease in albedo to incoming solar radiation, and in opacity to outgoing longwave radiation. At low latitudes the surface and troposphere heat, and at high latitudes in winter they cool. The change in meridional temperature gradient affects the rate of cyclogenesis, and the amplitude of planetary waves. For storm clouds, as in winter cyclones, the effect of increased ice formation is mainly to increase the rate of glaciation of lower level clouds by the seeder-feeder process. The increase in precipitation efficiency increases the rate of transfer of latent heat between the air mass and the surface. In most cyclones this is likely to result in intensification, producing changes in the vorticity area index as observed. Cyclone intensification also increases the amplitude of planetary waves, and shifts storm tracks, as observed. In this paper we first describe the production of space charge and the way in which it may influence the rate of ice nucleation. Then we review theory and observations of the solar wind modulation of J
z, and the correlated changes in atmospheric temperature and dynamics in the troposphere. The correlations are present for each input, (A, B, and C), and the detailed patterns of responses provide support for the inferred electrical effects on the physics of clouds, affecting precipitation, temperature and dynamics.

Influence of Solar Wind on the Global Electric Circuit, and Inferred Effects on Cloud Microphysics, Temperature, and Dynamics in the Troposphere

This article surveys the development of observational understanding of the interior rotation of the Sun and its temporal variation over approximately forty years, starting with the 1960s attempts to determine the solar core rotation from oblateness and proceeding through the development of helioseismology to the detailed modern picture of the internal rotation deduced from continuous helioseismic observations during solar cycle 23. After introducing some basic helioseismic concepts, it covers, in turn, the rotation of the core and radiative interior, the “tachocline” shear layer at the base of the convection zone, the differential rotation in the convection zone, the near-surface shear, the pattern of migrating zonal flows known as the torsional oscillation, and the possible temporal variations at the bottom of the convection zone. For each area, the article also briefly explores the relationship between observations and models.

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Solar Interior Rotation and its Variation

Many observations related to the large-scale structure of the interplanetary magnetic field, its solar origin and terrestrial effects are discussed. During the period observed by spacecraft the interplanetary field was dominated by a sector structure corotating with the sun in which the field is predominantly away from the sun (on the average in the Archimedes spiral direction) for several days (as observed near the earth), and then toward the sun for several days, etc. The average sector appears to be a coherent entity with internal structure such that its preceding portion is more active than its following portion. Cosmic rays corotate with the interplanetary field, and there are differential flows associated with the sector pattern. Profound effects on geomagnetic activity and the radiation belts are produced as the sector pattern rotates past the earth. The solar origin of the sector pattern is discussed. The solar source may be associated with the large-scale weak background photospheric fields observed with the solar magnetograph. It is suggested that there may be a rather continual relation between this solar structure and terrestrial responses, of which the recurring M-Region geomagnetic storms are just the most prominent example.

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The interplanetary magnetic field - Solar origin and terrestrial effects.

A simple linear filter is adapted for use in numerical models of the large-scale circulation to act in place of an explicit horizontal diffusion term in the equations. The filter can be shown to be ideally suited for this purpose in the sense that it can be made increasingly scale-dependent as the order of the filter is increased. The one-dimensional filter of order n is constructed from n three-point symmetrical operators and involves 2n/1 grid points. It is capable of eliminating two-grid-interval waves completely, yet allowing little or no damping of longer waves. In one space dimension, the use of the n = 1 order filter can be shown to be equivalent to the incorporation of a one-dimensional Fickian diffusion term in the differential equation. For any order n, the use of the one-dimensional filter is equivalent to the incorporation of a one-dimensional linear diffusion of order 2n. It is therefore apparent that as n increases, the ability of the filter to discriminate in its response to short-...

The Use of Linear Filtering as a Parameterization of Atmospheric Diffusion

Power spectral analyses have been carried out on a data set of Swedish visual auroras for the period 1721 to 1943. Besides the anticipated 11-year, annual, and semiannual cycles, an unexpected peak near 1.4 years is found. The amplitude of this latter peak, while smaller than that of the 6-month and 12-month peaks, is statistically significant at between the 5% and 1% level and is found consistently in a sequence of spectra covering consecutive, overlapping, approximately 22-year data segments. The semiannual variation becomes extremely weak during the prolonged solar activity minimum at the beginning of the nineteenth century, and also shows some lessening during the prolonged solar activity minimum near the beginning of the twentieth century. The 1.4-year peak shows a strong modulation of about 65 to 68 years and an additional long-term trend of the order of centuries. The origin of this peak is unknown.

Power spectral analysis of auroral occurrence frequency

A Neglected Cycle in Sunspot Numbers

Time series of a number of solar activity parameters are subjected to generalized harmonic analysis. This analysis allows the separation and comparison of phenomena which happen over a wide spectrum of time scales. It also allows comparison of variations on similar time scales in two different parameters. The analyses show for example that the correlation between radio noise at 2800 Mc/s and the Greenwich sunspot areas is almost unity. Other parameters such as an index of plage activity have spectra somewhat similar to sunspot spectra, but only a moderate degree of relationship to sunspot series. The data indicate that this lack of correspondence is due in large measure to ‘noise’ in the plage data. An index of flare activity has an almost white noise spectrum, no maximum corresponding to the solar rotation period, and no relationship to sunspots.

Decomposition and comparison of time series of indices of solar activity

A high-resolution power spectrum of 72 years of daily values of the international magnetic character figure, Ci, shows two subsidiary peaks on either side of the well-known 27-day period. The larger of the two subsidiary peaks is situated close to the lunar synodic period of 29.53 days. The origin of the subsidiary peaks is examined. A lunar association is rejected as a significant causal agent, along with various errors and bias. It is concluded that the subsidiary peaks represent some real phenomenon and are probably produced by solar activity, although perhaps indirectly.

Ralph Shapiro

Papers

The Use of Linear Filtering as a Parameterization of Atmospheric Diffusion

Power spectral analysis of auroral occurrence frequency

A Neglected Cycle in Sunspot Numbers

Decomposition and comparison of time series of indices of solar activity

Three peaks near 27 days in a high‐resolution spectrum of the international magnetic character figure, Ci