On the influence of climatic factors on the ratio between the cosmogenic isotope 14C and total carbon in the atmosphere in the past

Radiocarbon ¹⁴C is a cosmogenic isotope, which is most extensively used by scientists from a wide variety of fields. Its rate of generation in the atmosphere depends on solar modulation and thus, studying ¹⁴C concentration in natural archives, one can reconstruct solar activity level in the past. The paper shows results of box-model calculations of generation of the ¹⁴C isotope in the atmosphere and its relative abundance during the time interval 1389–1800 AD, taking into account influence of changing climate. This interval includes the deep minimum of solar activity and period of significant change in atmospheric concentration of CO₂ and global temperature. The performed analysis showed that concentration of ¹⁴C in the atmosphere reflects not only variations of the galactic cosmic rays intensity but as well changes of temperature and atmospheric CO₂ concentration. It is shown that the decrease in CO₂ concentration in the atmosphere during 1550–1600 can be connected with absorption of CO₂ by the ocean surface layer. Thus, taking into account the climatic changes is an important condition for the reconstruction of solar activity in the past using data based on cosmogenic isotopes.     

Desiring structures: exhibiting the dendritic form

Abstract

From 30 April to 4 September 2005, the Museum of Design in Zurich staged the exhibition 'Simply complex' ('einfach Komplex'), an exploration of the dendritic form. The dendritic form is a recurrent and often instructive one in the sciences, which can be observed in many contexts and at different scales, from the delta of liquid methane revealed by the Huygens probe on the surface of Saturn's moon Titan in 2005, to micrographs of neurons in the human brain. It also recurs in the form of the persuasive diagrams which art historians, linguists and philosophers have long used to bring forth a sense of organic unity, order and development from their data. 'Simply complex' displayed case studies of these visual strategies in the sciences, while also showcasing some specially commissioned critical and aesthetic interventions by artists on the theme of the branching form. Here I reflect on the planning process for the exhibition, and present for the first time in English my essay from the accompanying book.     

Electrical structure in the high-latitude middle atmosphere

Middle atmosphere electrodynamics at high latitudes differs significantly from the normally assumed picture of a passive region through which electric fields of external origin couple. Large Vm ⁻¹ electric fields, both horizontal and vertical, have been observed within bounded regions of the upper stratosphere and lower mesosphere. They seem to occur only in regions where the electrical conductivity is a few times 10⁻¹⁰ S m⁻¹ or less and appear to be current limned. While low conductivity is necessary, it is not a sufficient condition for occurrence. The observed large horizontal electric fields were found to be anticorrelated with the local neutral wind. However, a generation mechanism of these electric fields is as yet unknown but must involve space charge separation rather than dynamo effects. Large variations in the conductivity were also observed to occur with fluctuations in magnetic activity, and these were found to be consistent with measured variations in energy deposition during auroral phenomena. Theoretical concepts of mapping of electric fields downward from the thermosphere along equipotential magnetic field lines were shown to hold qualitatively in the D-region at the mV m⁻¹ level. Perturbations affecting such models were determined to be small.     

Middle atmospheric electrodynamics: status and future

Middle atmospheric electrodynamics is a field stimulated by the recent discovery that large electric fields may occasionally exist in the mesosphere and upper stratosphere. The measurements suggest V m⁻¹ magnitudes for these fields, which have been reported to occur in both horizontal and vertical configurations. Since they are usually confined within bounded height regions, they might be of local origin. Although the measurements are still considered controversial, the implications of such fields, if real, could be important. Should these fields persist in both space and time, they could perturb the global electric circuit with a component subject to modulation by phenomena related to solar activity. This might help explain the numerous correlations which exist for tropospheric electrical response to solar and geomagnetic activity. Further work is now required to validate the earlier findings and determine the morphology and extent of the large electric fields. Experiments must also be derived and conducted to determine the physical origin of such fields and their relationships to external influences, such as magnetospheric electric fields and tropospheric thunderstorms. The current status of results regarding V m⁻¹ fields in the middle atmosphere is reviewed in perspective with the more widely accepted electric field structure established for this region from balloon and rocket data. Other factors such as ion conductivity, ion mobility and aerosols are also considered for their potential influence on the middle atmospheric electrical environment.     

Schumann resonance effects of electrical conductivity perturbations in an exponential atmospheric/ionospheric profile

Eigenmode solutions are computed for the n = 1 … 3 Schumann resonances in a perturbed, unmagnetized vertical atmospheric conductivity profile σ = 10⁻¹⁶ exp (z/3.1) mho m⁻¹ for z ⩽ 100 km and σ = 10⁻² mho m⁻¹ for z > 100 km. For the unperturbed exponential profile the radial electric field E_r is nearly constant z ≲ 40 km, and decreases rapidly above 50 km. The tangential field E_ϑ > E_r for z ≳ 65 km. The Joule dissipation profile in this case has an absolute maximum at about 50 km and a smaller relative maximum at 90 km with a deep relative minimum at 65 km. The maximum dissipation thus occurs in the middle atmosphere, making the Schumann resonances particularly susceptible to conductivity perturbations in this region. The perturbations of this study comprise Gaussian-shaped enhancements or depressions of FWHM ≈ 10 km impressed on the unperturbed profile. Eigenfrequencies and Q-values are computed for the full range of perturbation amplitudes 10⁻³−10³ and altitudes 30–90 km. The perturbations induce overall eigenfrequency variations of ± 1.0, ±1.5, and ±2.5 Hz in the n = 1, 2, and 3 modes, respectively, and Q-values spanning the range 3.5–11.0. The results of this calculation extend those of previous works investigating the Schumann resonance response to atmospheric conductivity perturbations, and may be useful for interpreting experimental observations in terms of external ionization source intensities of GCR, Lyman-α, or solar cosmic or X-rays, or variations in middle atmospheric chemical constituents.     

Response of ‘atmospheric’ lightning to systematic changes in the global electric field

A wide-angle photomultiplier system has detected optical pulses of lightning origin while searching for atmospheric fluorescence emissions from cosmic X-ray and gamma ray bursts. A broad-band spectral analysis of these events has helped identify lightning discharges which preferentially occur in the atmosphere and are similar in morphology to the ‘A-events’ seen by previous fluorescence experiments elsewhere. We show here that these events are facilitated by increases in the global fair-weather potential gradient, occurring as a result of its diurnal variation or brought about by a decrease in the flux of the galactic cosmic radiation that may accompany moderate changes in the level of geomagnetic activity.     

Evaluation of electron and ion densities in the middle atmosphere from rocket-borne blunt probes

Detailed consideration has been given to the determination of electron number densities from conductivity data gathered by rocket-borne blunt probes in the middle atmosphere, and the intercomparison of these electron densities with those derived from other diagnostics. A definition of the difficulty of electron density determination from rocket-borne probes is presented. Also, the procedures for the determination of ion densities from blunt probe data in the middle atmosphere are critically evaluated. General aspects of particle collection by supersonic probes are compared with those of subsonic probes. It is noted that strong (× 10) compression regions will form in front of supersonic probes at altitudes up to 100 km, and the altered electron attachment rates could significantly affect indicated electron and negative ion concentrations. A summary of new analysis for determining electron densities from negative conductivities taken with a subsonic blunt probe is presented and the analysis is applied to data on several days where intercomparisons are possible. Blunt probe data from 31 January 1972 and 5 December 1972 (WI),² and 2 October 1975 and 29 September 1977 (WSMR)³ are reduced to predict electron density profiles. In the region of intercomparison, there is general agreement in the electron density predictions. The indications of electron density at altitudes below 70 km are new, and predict a region of moderately enhanced densities down to 45 km.     

Estimation of initial auroral proton energy fluxes from Doppler profiles

An energetic auroral proton entering the atmosphere will, by charge exchange in collisions with atmospheric constituents, alternate between being a proton H⁺ and a neutral hydrogen atom H. This study provides a procedure to evaluate the auroral Doppler shifted and broadened hydrogen Balmer profile as a function of initial energy, flux, pitch angle and view angle relative to the geomagnetic field. The differential proton energy flux entering the atmosphere is deduced using ground-based measurements of H_α and H_β from Nordlysstasjonen in Adventdalen, Longyearbyen. The main assumptions are that the geomagnetic field lines are: parallel and vertical, and that the pitch angle of the H/H⁺-particle is preserved in collisions with atmospheric constituents before being thermalized. This numerical method estimates the fate of the auroral H/H⁺-particle in the atmosphere, and from measured Doppler profiles the corresponding incoming particle flux can be deduced. Optimization of the method will continue through extensive use of observational data.     

First summer results on winds in the upper mesosphere derived from the 843 nm hydroxyl emissions measured from the Bear Lake Observatory,Utah

The Imaging Fabry-Perot Interferometer (IFPI) at the Bear Lake Observatory (BLO), Utah (41.9°N, 111.4°W) is used for studies of the aeronomy of the middle and upper atmosphere. Wind and temperature structure can be determined from observations of the Doppler shift and Doppler broadening of the airglow and auroral emissions from the mesosphere and thermosphere. The mesospheric winds recorded at the end of August, September and early October 1992 are consistent with a semi-diurnal tidal variation. The amplitude of this variation is approximately 30 ms⁻¹ at the end of August and early September and approximately 20 ms⁻¹ at the end of September and early October. However, during June and July, the semi-diurnal tidal variation, if present, is weak, with amplitude < 5 ms⁻¹. No consistent semi-diurnal tidal variation is observed during late October 1992. During the solstice period, antisymmetric tidal components may be preferentially generated in such a way that they can result in destructive interference with the normally dominant symmetric modes, resulting in a decrease of tidal variation. This is consistent with the observed decrease in tides during the June, July and late October periods. Near the equinoxes, however, the excitation of these antisymmetric modes is expected to be weaker, possibly explaining why a pronounced and consistent semi-diurnal tidal variation has been observed during the August, September and early October periods. In contrast, the mesospheric winds derived from the Sheffield Meteor Wind Radar (53.4°N, 1.5°W) reveal a clear semi-diurnal tidal variation throughout the year, with an amplitude that may vary between 15 ms⁻¹ and 50 ms⁻¹, being about 25 ms⁻¹ on average. The IFPI records winds from a region of the atmosphere centred at 87 km, whereas the Sheffield Meteor Wind Radar measures winds centred at 95 km. Therefore, the two regions may experience different tidal modes due to the different latitude, longitude and altitude of the observed regions and/or the different topography of the observing sites. Some proposed reasons for these differences are presented.     

Comparison of stratospheric ozone profiles retrieved from microwave-radiometer and Dobson-spectrometer data

Passive Microwave Remote Sensors (MRS) can provide information on the composition of the atmosphere by measuring the thermal radiation emitted from rotational transitions of atmospheric molecules Ozone profiles simultaneously obtained from an MRS and a Dobson instrument (‘Umkehr’ method) are compared over a time period of approximately four months. The microwave measurements yield ozone concentrations which are 20–30% higher than the ‘Umkehr’ values. A critical, though not well known, parameter for the microwave inversion procedure is the foreign gas pressure broadening parameter (C) for the observed 142GHz ozone resonance. Throughout the intercomparison we used a value of 3 MHz mb⁻¹. There is recent theoretical and experimental indication that C is more likel y to be as low as 2.5 MHz mb⁻¹. If we use this new value for C all microwave retrieved profiles decrease by 20–25%, thus leading to a far better agreement with the ‘Umkehr’ results. Our measurements therefore strongly support the proposed value of 2.5 MHz mb⁻¹. A final answer on MRS ‘Umkehr’ correlation accuracy cannot be given. We feel that comparison on a day-to-day basis may be rather meaningless and monthly mean values should be used. On the other hand, there was relatively little change in these mean values during the intercomparison period The MRS showed its potential to retrieve ozone profiles also under adverse meteorological conditions, such as cloud cover or fog.     

Electrical characteristics of winter lightning

To make clear the characteristics of winter lightning flashes, the long term observation of winter lightning on the west coast of Japan has been continued using magnetic links, digital recording systems for the current oscillograms, field mills, still cameras and video camera systems for the images of lightning channels. Of the 66 magnetic links records exceeding 2 kA, 73% were negative in polarity, and 27% were positive. Median peak values for winter flashes were 17 kA for negative flashes and 45 kA for positive flashes, respectively. 145 current waveforms for the winter lightning flashes, which have current amplitudes exceeding 1 kA, have been obtained by the shunt systems and/or the coils system. They show that winter lightning flashes often have a very long duration or continuing current, and sometimes have a very large amplitude exceeding 200 kA in positive flashes. As one example flash on 9 January 1987, the maximum current amplitude was +280 kA, the maximum current derivative 1.0 × 10¹⁰ As⁻¹, the total charge +400 C and the action integral 1.5 × 10⁷ A²s. The winter lightning current waveforms are classified into three types: single stroke flashes, monopolar multiple stroke flashes and bipolar flashes. Moreover, each flash is categorized as positive or negative, single peak or multiple peak, and with or without a continuing current.     

On the role of dust in the summer mesopause

We propose that dust formed at the cool summer mesopause may have optical properties very different from that measured for bulk material of ice. The smallness of the dust and possible surface impurities may lead to high photoelectric yields and low workfunctions. For such reasons the dust in the summer mesopause may, at least occasionally, be charged to substantial positive surface potentials while pure ice, with its high photoelectric workfunction, would be charged to low and negative potentials by collisions with plasma particles. The presence of ‘dressed’ dust particles, with surface potentials of some volts, can lead to enhanced radar backscatter. We also suggest that the apparent reductions in electron density (‘bite-out’), which have been observed in the radar backscatter region, can be caused by the inability of an electrostatic probe to deflect the massive dust particles.The dust density which is required by our model to explain radar backscatter and electron bite-outs is of the order of 10 cm⁻³ for dust of radius above 5 × 10⁻⁶ cm.     

The solar eclipse of 26 February 1979: analysis and modelling of primary pair production,electron density and ionic composition

The solar eclipse of 26 February 1979 was observed from Red Lake, Canada, (52 °N, 91 °W) where totality occurred at about 1053 local time. Several research groups and government agencies participated in an extensive ground- and rocket-based observational program directed at the middle atmosphere. At the time of the eclipse, an extensive geomagnetic storm was in progress and the middle atmosphere was undergoing temperature and circulation changes associated with a stratospheric warming. Concurrent observations of atmospheric constituents, solar radiation, electron flux and other middle atmosphere parameters were obtained as inputs for a D-region predictive chemical computer code, DAIRCHEM, tailored to eclipse conditions. Ion pair production rates were computed by an E-region infrared radiance model and were used as necessary source function input values for DAIRCHEM computations. The computations yielded predictions of electron and total positive ion densities about totality. The positive ion measurements of a supersonic Gerdien condenser and a subsonic blunt probe during the eclipse were in agreement with the model computations and provided normalizing summations of total positive ions for the interpretation of mass spectrometer measurements. The chemical computer code identified principal routes for increase and removal of key species such as O₂⁺, NO⁺, hydrated clusters and negative ions. The dominant precursor ion for pair production hydrates was O₂⁺ and the chemistry was characteristic of the disturbed D-region.     

A simple model of gravity-wave momentum and energy fluxes transferred through the middle atmosphere to the upper atmosphere

Vertical fluxes of momentum and energy through the middle atmosphere are calculated by using a simple semi-empirical model of quasi-monochromatic internal gravity waves with dominant vertical wavenumbers. In this model those dominant gravity waves are assumed to saturate and break at each observational altitude by an effective critical-layer mechanism. The dominant value of the vertical wave-number is expressed by an exponential function of altitude, decreasing upward with a scale height of 34 km. This expression gives the momentum and energy flux densities decreasing upward with scale heights of 12 and 18 km, respectively, and typical values at 100 km altitude are estimated as 4 × 10⁻⁵ Pa and 4 × 10⁻³ W/m². A heat flux induced by wavebreaking turbulence also has an order of magnitude similar to that of the wave energy flux. Variabilities around these values and comparisons with other momentum and heat inputs to the upper atmosphere are only briefly discussed.     

Measurement of O2(a1Δg) emission in a total solar eclipse

The altitude distribution of the oxygen infrared atmospheric bands at 1.27 μm was measured during the total solar eclipse of 26 February 1979. The ozone concentration profile has been derived from these airglow measurements and indicates that at 85 km the concentration at totality was 7 × 1.7 cm⁻³, with no well defined upper layer. This reduced concentration, which is typical of summertime conditions, was probably due to perturbations in the mesospheric chemistry and transport induced by a winter warming event that was in progress at the time of the eclipse. At 60 km the ozone concentration, 2.7 × 10¹⁰ cm⁻³, was enhanced above that normally measured. This increase may also have been caused by the stratospheric warming event but the effects of a particle precipitation event, which was also in progress during the eclipse, may be important.     

Measurement of the eddy diffusion coefficient of the middle atmosphere from a balloon at low latitude

A great deal of uncertainty exists concerning the distribution of the vertical eddy diffusion coefficient of the middle atmosphere. A new technique has been developed in this laboratory in which chemical clouds are released in the middle atmosphere from a balloon platform. The expansion of the cloud is monitored by ground photography, from which the value of the eddy diffusion coefficient is calculated. The experiment was successfully tested on 9 March 1985 at Hyderabad (17.5°N, 78.6°E), India. The value of the coefficient was found to be of the order of 10⁴ cm² s⁻¹ in the altitude range 10–20 km.     

Atmospheric X-rays at 11°S geomagnetic latitude

X-ray measurements at balloon altitudes were made at São José dos Campos, Brasil (23°12′S, 45°51′W geographic coordinates, ~11°S geomagnetic latitude) on 18 December 1981, using an omnidirectional NaI(T1) scintillation detector. Atmospheric X-rays, namely secondary X-radiation from cosmic rays, were measured for the energy interval 30–155 keV and up to an atmospheric depth of 5.5 g cm⁻². A comparison of the flux measured at the Pfotzer maximum during these measurements with those obtained previously by several research groups at other latitudes and with a similar technique has also been made. Finally, a comparison of the atmospheric component with that attributed to the diffuse component is also presented and it is concluded that both components are of about the same magnitude at ~ 5 g cm⁻² and at ~ 11°S geomagnetic latitude.     

Variability of d-region electron densities at tromsø

The 2.75 MHz partial-reflection radar at Ramfjordmoen near Tromsø has been used for a study of D-region electron densities by the differential-absorption method on a number of days during 1978–79. Received signals are generally stratified in several layers, typically over 60–80 km. Strong stable echoes are seen down to 55 km during periods of enhanced riometer absorption. Inferred electron densities vary between ~ 100–1000 cm⁻³ at ~ 60–80 km and show well-defined features which persist for ~ 10–20 min. During periods of high absorption, enhanced electron densities (~ 600 cm⁻³) are observed below 65 km. During a Polar Cap Absorption event, the inferred electron densities at 60–70 km show a very stable profile. Possible sources of D-region ionization at high latitudes are briefly discussed     

Fixing the Hole in the Bucket: Household Poverty Dynamics in the Peruvian Andes

Achieving the Millennium Development Goal of halving poverty will require simultaneous action on two separate fronts: helping poor people escape from poverty, and stemming the flow of people into poverty. This article examines forty Peruvian communities, and finds that descents into poverty have occurred alongside escapes in every one of them. Escape and descent are asymmetric in terms of reasons: while one set of reasons is responsible for escapes from poverty, another and different set of reasons is associated with descent. Making progress in poverty reduction will require measures to accelerate escapes whilst at the same time slowing down descents. The article looks at the different policies which will be required to serve these two separate purposes.     

Riming electrification mechanism for charge generation within a thundercloud

A time dependent model for the rate of growth of the electric field within a thundercloud by the process of graupel formation (riming electrification) has been presented. The parameters of the model are: p₀, the precipitation intensity; q, the charge acquired by the graupel in each collision it makes with an ice crystal and 〈p〉, the charge transfer efficiency. Sets of values for the field growth and the maximum field have been obtained by varying these parameters.It is found that the estimated field for the initiation of a lightning flash (3.4 × 10⁵Vm⁻¹) within a time of about 1200 s can be achieved, taking a reasonable value of q = −1.67 × 10⁻¹⁴ C only for P₀ ≳ 5.56 × 10⁻⁶ms⁻¹(20 mmh⁻¹) and 〈p〉 ≳ 0.5. The maximum attainable electric field, E_max, itself is not sensitive to the value of q, within a reasonable range of variation in it (for a given p₀), but its rate of growth is: it grows faster, if g is larger.