Radar observations of auroral zone flows during a multiple-onset substorm

We present an analysis of ground magnetic field, ionospheric flow, geosynchronous particle, and interplanetary data during a multiple-onset substorm on 12 April 1988. Our principal results concern the modulations of the ionospheric flow which occur during the impulsive electrojet activations associated with each onset. During the first hour of the disturbance these take place every \sim12.5 min and involve the formation of a new intense westward current filament in the premidnight sector, just poleward of the preexisting extended current system driven by the large-scale flow. These filaments are \sim1 h MLT wide (\sim600 km), and initially expand poleward to a width of \sim300 km before contracting equatorward and coalescing with the preexisting current, generally leaving the latter enhanced in magnitude and/or expanded in latitude. Within the impulsive electrojets the flow is found to be suppressed to values 50–100 m s⁻¹ or less during the first few minutes, before surging equatorward at 0.5-1.0 km s⁻¹ during the phase of rapid coalescence. The implication is that the precipitation-induced Hall conductivity within the impulsive electrojet initially rises to exceed \sim100 mho, before decaying over a few minutes. This value compares with Hall conductivities of \sim20 mho in the quasi-steady current regions, and a few mho or less in the regions poleward of the electrojets and in the preonset ionosphere. Preliminary evidence has also been found that the flow surges propagate from midnight to the morning sector where they are associated with arrested equatorward motion or poleward contractions of the current system. These observations are discussed in terms of present theoretical paradigms of the global behaviour of fields and flows which occur during substorms.     

Petrology of the Hopen mangerite-charnockite intrusion, Lofoten, north Norway

The Hopen massif, intrusive age 1900 m.y., exposed area 15 km², in the Lofoten-Vesterålen granulite facies province has the mineral assemblages: (1) mesoperthite+plagioclase (An_7–20)+quartz+clinopyroxene (Di_20–25)+orthopyroxene En_15–25+opaques±minor amphibole±minor biotite; (2) mesoperthite+plagioclase (An <2)+quartz+clinopyroxene (Di <10)+olivine Fe lt;5)+opaques. By using mineral and whole rock analyses, the crystallization conditions were estimated to be 1000°C, 12 kb load pressure and an oxygen fugacity approximately corresponding to the WM buffer. Rocks with the assemblage of type (2) contain secondary orthoferrosilite (Fe_0.90–0.95Mn_0.04–0.07Mg_0.01Ca_0.01)₂Si₂O₆, generated by reactions involving fayalite, magnetite and quartz at 800°C, 10kb load pressure and at oxygen fugacities approaching QFM buffer conditions. Subsequent to a crustal thickening, the mangeritic rocks in Lofoten-Vesterålen were emplaced in a tensional environment comparable with modern continental rifts. A ‘gabbro pillow’ magma chamber at the crustal base is proposed as parental magma for the mangeritic rocks, of which the Hopen massif represents a late differentiation.     

Tropical cyclones in enhanced resolution CMIP5 experiments

This study investigates the possible effects of global warming on tropical cyclone (TC) activity. The study is conducted using the coupled ocean–atmosphere global climate model EC-Earth configured at a relatively high resolution (T159 with 62 vertical levels), which is integrated following the CMIP5 protocol. By considering the late twentieth century (1979–2009) in the historical simulation and the twenty-first century end (2070–2100) in the RCP4.5 and RCP8.5 scenarios, significant future annual mean frequency decreases are found globally and in both hemispheres, accompanied by significant mean lifetime decreases and significant intensity increases, the latter being found through several different measures (but with caveats). In addition, the relatively novel aspect of simulating TCs of the past (1900–1930) is studied to further assess the robustness of the climate change results. These results suggest that TCs in the early twentieth century were more frequent in the southern hemisphere and dissipated more energy in the southern hemisphere and the South Indian Ocean. Although some model biases are present and the coarse model resolution prevents intense TCs in being simulated, reasonable TC simulation skill for other metrics (e.g., TC genesis, frequency of occurrence) is found when validated against present day observations. Thus the model displays an acceptable ability to connect TC climatology with the larger scale circulation.     

A multipoint study of a substorm occurring on 7 December, 1992, and its theoretical implications

On 7 December 1992, a moderate substorm was observed by a variety of satellites and ground-based instruments. Ionospheric flows were monitored near dusk by the Goose Bay HF radar and near midnight by the EISCAT radar. The observed flows are compared here with magnetometer observations by the IMAGE array in Scandinavia and the two Greenland chains, the auroral distribution observed by Freja and the substorm cycle observations by the SABRE radar, the SAMNET magnetometer array and LANL geosynchronous satellites. Data from Galileo Earth-encounter II are used to estimate the IMF B_z component. The data presented show that the substorm onset electrojet at midnight was confined to closed field lines equatorward of the pre-existing convection reversal boundaries observed in the dusk and midnight regions. No evidence of substantial closure of open flux was detected following this substorm onset. Indeed the convection reversal boundary on the duskside continued to expand equatorward after onset due to the continued presence of strong southward IMF, such that growth and expansion phase features were simultaneously present. Clear indications of closure of open flux were not observed until a subsequent substorm intensification 25 min after the initial onset. After this time, the substorm auroral bulge in the nightside hours propagated well poleward of the pre-existing convection reversal boundary, and strong flow perturbations were observed by the Goose Bay radar, indicative of flows driven by reconnection in the tail.     

High voltage transmission lines and their effect on reindeer: a research programme in progress

We review literature on high voltage transmission lines and their effect on wild reindeer ( Rangifer tarandus ) migration patterns and area use. We conclude that reliable knowledge is lacking on the effects of transmission lines on reindeer ecology. This condition relates to the lack of long-term monitoring of reindeer migration patterns in relation to existing lines. It is also related to the fact that nothing is known about hearing in reindeer (or any other deer species in Norway) in relation to transmission line noise, which is considered an obstacle for migrating reindeer.
We then outline a research programme that includes a laboratory study to determine the audiogram in reindeer and two field studies to examine the proximate effects of transmission lines - independently as well as combined with ambient environmental variables - on reindeer behaviour. The audiogram in two yearling male reindeer has been determined; this part of the study will be completed this year with the determination of a corresponding audiogram in two female yearlings. The behaviour study of domestic reindeer under high voltage transmission lines was completed in September 1999. The behaviour study of wild reindeer in the area crossed by a 420 kV power line will continue this year and its completion is anticipated in 2001.     

Barents-Kara sea ice and European winters in EC-Earth

Climate Dynamics - The potential link between decreasing Barents-Kara sea ice and cold winters in Europe is investigated using the enhanced resolution (horizontal atmospheric resolution of $$\sim...     

Comment on “Trends and low frequency variability of extra-tropical cyclone activity in the ensemble of twentieth century reanalysis” by Xiaolan L. Wang,Y. Feng,G. P. Compo,V. R. Swail,F. W. Zwiers,R. J. Allan,and P. D. Sardeshmukh,Climate Dynamics, 2012

The main subject of this article is to comment on the issue of storminess trends derived from the twentieth century reanalysis (20CR) and from observations in the North Atlantic region written about in Wang et al. (Clim Dyn 40(11–12):2775–2800, 2012). The statement that the 20CR estimates would be consistent with storminess derived from pressure-based proxies does not hold for the time prior to 1950.     

EISCAT observations of unusual flows in the morning sector associated with weak substorm activity

A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at \sim0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (\sim0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is “pinched off”, and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked “viscous-like” momentum transfer across the magnetopause.