Galaxy And Mass Assembly (GAMA): data release 4 and the z < 0.1 total and z < 0.08 morphological galaxy stellar mass functions

Galaxie

Modelling studies of the effects of cusp inputs on the polar ionosphere

A new numerical model of the high latitude ionosphere is used in conjunction with data from the EISCAT radar facility to study the formation and structure of polar patches. Inputs based on the ionospheric signature of a Flux Transfer Event (FTE) are used in the model. It is found that a region of decreased O+ and increased molecular ion concentration is produced in the cusp region of the polar ionosphere. Ion temperatures are observed to be greatly enhanced in this region, which leads to an increase in the recombination rate resulting in the alteration of the ion concentrations. The electron temperature is less enhanced than the ions. Large upward fluxes transport plasma to higher altitudes where it is stored and released several hours after the FTE has finished, as the flux tube convects across the polar cap

Model plasmasphere calculations for L-values near 2.5 at the longitude of Argentine Islands, Antarctica

A model of the terrestrial plasmasphere that includes an eccentric dipole geomagnetic field has been developed. Calculations are carried out for tubes of plasma at the longitude of Argentine Islands, Antarctica (64°W). Results for L-values around 2.5 are compared with those obtained in VLF experiments at Faraday that detect whistler signals from NAA and NSS stations in the north east U.S.A. Calculated group delay and Doppler shift of whistler signals are analysed by the usual technique employed by experimenters at Faraday to deduce meridional E×B plasma drift and rate of change of plasma tube content (i.e. ionosphere-plasmasphere flux). The deduced drifts and fluxes are compared with those from the model

The role of ion drift in the formation of ionisation troughs in the mid- and high-latitude ionosphere—a review

F-layer ionisation troughs are frequently observed in the sub-auroral and high-latitude ionospheres. We define the mid-latitude trough as the region of low plasma concentration at F-region altitudes that occurs near the equatorward side of the low latitude edge of the energetic electron precipitation boundary of the auroral oval. High latitude troughs are simply defined as troughs that occur in the auroral oval and polar cap. We review the progress that has been made in describing the phenology and morphology of the mid-latitude trough since the review by Moffett and Quegan [(1983), J. atmos. terr. Phys. 45, 315]. We also provide the first summary of observations of the high latitude trough. We then go on to describe the physical processes which can lead to trough formation. We discuss separately the importance of production, loss and both vertical and horizontal transport for the formation ofF-region troughs. We conclude that the consequences of ion velocity in the rest frame of the neutral particles is of paramount importance for trough formation through dynamical and chemical processes. We consider the geophysical conditions and the locations where trough formation is most likely both during relatively quiescent geomagnetic periods and during periods when high latitude electric fields are large and varying rapidly with time. We describe the characteristics of the resultant troughs, such as electron and ion temperatures and ionic composition. We propose a new, more rigourous definition for sub-auroral ion drift events (SAIDs) based upon ion motion in the neutral particle rest frame. Sophisticated computer modelling of several situations is provided to support the tenets of the trough formation presented in the paper. Despite the unifying theory of trough formation presented here, several areas for further theoretical, computational and observational study are identified

Seasonal and longitudinal effects on plasmaspheric tube content

A mathematical model of the ionosphere and plasmasphere that includes an eccentric dipole geomagnetic field has been constructed to model, in the first instance, whistler results at L = 2.5. Observations show that there is a pronounced annual variation in plasmaspheric tube content at mid-latitudes and that this effect is modulated by longitude. The model results indicate that the geometry of the magnetic field (in terms of geographic coordinates) is a major factor in determining the magnitude of the annual variation, with neutral air winds and the degree of plasmaspheric refilling also important. A global variation in neutral atomic hydrogen abundance appears to have little influence

Resistance to common bacterial blight in selected accessions of Phaseolus species

Nine P. accessions showed consistent reactions to common bacterial blight (Xanthomonas campestris pv. phaseoli) in 2 field trials and 1 greenhouse test

Analysis of magnetometer data using wavelet transforms

Geomagnetic eld-line resonances may be identi ed via the use of cross-phase analy-sis of data from two closely spaced meridional ground-based magnetometer stations. It has been demonstrated that preprocessing of the data using a wavelet-based lter, chosen with regard to the variance of coe ¯ cients of the wavelet components, can be used to remove both low-frequency trend and large amplitude, localized struc-tures, thus facilitating the selection of the eigenfrequency. We demonstrate that the dependence of the variance of coe ¯ cients on the wavelet level during a geomagnetic storm event is characteristically di¬erent from that obtained from data on a day associated with quiet geomagnetic activity. This suggests that the spectral nature of magnetic disturbances excited in the magnetosphere is dependent upon the level of geomagnetic activity

Annual and semiannual variations in the ionospheric F2-layer: I Modelling

Annual, seasonal and semiannual variations of F2-layer electron density (NmF2) and height (hmF2) have been compared with the coupled thermosphere-ionosphere-plasmasphere computational model (CTIP), for geomagnetically quiet conditions. Compared with results from ionosonde data from midlatitudes, CTIP reproduces quite well many observed features of NmF2, such as the dominant winter maxima at high midlatitudes in longitude sectors near the magnetic poles, the equinox maxima in sectors remote from the magnetic poles and at lower latitudes generally, and the form of the month-to-month variations at latitudes between about 60°N and 50°S. CTIP also reproduces the seasonal behaviour of NmF2 at midnight and the summer-winter changes of hmF2. Some features of the F2-layer, not reproduced by the present version of CTIP, are attributed to processes not included in the modelling. Examples are the increased prevalence of the winter maxima of noon NmF2 at higher solar activity, which may be a consequence of the increase of F2-layer loss rate in summer by vibrationally excited molecular nitrogen, and the semiannual variation in hmF2, which may be due to tidal effects. An unexpected feature of the computed distributions of NmF2 is an east-west hemisphere difference, which seems to be linked to the geomagnetic field configuration. Physical discussion is reserved to the companion paper by Rishbeth et al

Annual and semiannual variations in the ionospheric F2-layer: II. Physical discussion

The companion paper by Zou et al. shows that the annual and semiannual variations in the peak F2-layer electron density (NmF2) at midlatitudes can be reproduced by a coupled thermosphere-ionosphere computational model (CTIP), without recourse to external influences such as the solar wind, or waves and tides originating in the lower atmosphere. The present work discusses the physics in greater detail. It shows that noon NmF2 is closely related to the ambient atomic/molecular concentration ratio, and suggests that the variations of NmF2 with geographic and magnetic longitude are largely due to the geometry of the auroral ovals. It also concludes that electric fields play no important part in the dynamics of the midlatitude thermosphere. Our modelling leads to the following picture of the global three-dimensional thermospheric circulation which, as envisaged by Duncan, is the key to explaining the F2-layer variations. At solstice, the almost continuous solar input at high summer latitudes drives a prevailing summer-to-winter wind, with upwelling at low latitudes and throughout most of the summer hemisphere, and a zone of downwelling in the winter hemisphere, just equatorward of the auroral oval. These motions affect thermospheric composition more than do the alternating day/night (up-and-down) motions at equinox. As a result, the thermosphere as a whole is more molecular at solstice than at equinox. Taken in conjunction with the well-known relation of F2-layer electron density to the atomic/molecular ratio in the neutral air, this explains the F2-layer semiannual effect in NmF2 that prevails at low and middle latitudes. At higher midlatitudes, the seasonal behaviour depends on the geographic latitude of the winter downwelling zone, though the effect of the composition changes is modified by the large solar zenith angle at midwinter. The zenith angle effect is especially important in longitudes far from the magnetic poles. Here, the downwelling occurs at high geographic latitudes, where the zenith angle effect becomes overwhelming and causes a midwinter depression of electron density, despite the enhanced atomic/molecular ratio. This leads to a semiannual variation of NmF2. A different situation exists in winter at longitudes near the magnetic poles, where the downwelling occurs at relatively low geographic latitudes so that solar radiation is strong enough to produce large values of NmF2. This circulation-driven mechanism provides a reasonably complete explanation of the observed pattern of F2 layer annual and semiannual quiet-day variations