A linear auroral current-voltage relation in fluid theory

Progress in our understanding of auroral currents and auroral electron acceleration has for decades been hampered by an apparent incompatibility between kinetic and fluid models of the physics involved. A well established kinetic model predicts that steady upward field-aligned currents should be linearly related to the potential drop along the field line, but collisionless fluid models that reproduce this linear current-voltage relation have not been found. Using temperatures calculated from the kinetic model in the presence of an upward auroral current, we construct here approximants for the parallel and perpendicular temperatures. Although our model is rather simplified, we find that the fluid equations predict a realistic large-scale parallel electric field and a linear current-voltage relation when these approximants are employed as nonlocal equations of state. This suggests that the concepts we introduce can be applied to the development of accurate equations of state for fluid simulations of auroral flux tubes.<br><br><b>Key words.</b> Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions) – Space plasma physics (kinetic and MHD theory

Generation mechanism for VLF chorus emissions observed at a low-latitude ground station

A detailed spectral analysis of VLF chorus emissions observed at the low-latitude ground station Gulmarg (geomag. lat., 24° 26' N, geomag. long., 147° 9' E, <i>L</i>=1.28) during the strong magnetic activity on 7-8 March 1986 have been carried out, which shows that each chorus element originates from the upper edge of the underlying hiss band. To explain various temporal and spectral features of these emissions, a possible generation mechanism has been presented based on the backward wave oscillator regime of the magnetospheric cyclotron maser. On the basis of this model, we have computed various chorus parameters as well as some magnetospheric parameters affecting the generation process. A comparison of the observed chorus characteristics with the proposed generation mechanism shows a good agreement

Fästingrelaterad problematik och prevention i stadslandskapets rekreationsmiljöer

En ökande och mer krävande medelklass i urbana miljöer kommer att innebära utmaningar för framtiden. Jag har noterat att urbana människor ofta ägnar sig åt utomhusaktiviteter, såsom löpning, skogspromenader, skidåkning och i vissa fall utövas mer specifika intressen som studier av växter, insekter eller fåglar. Problemet med de vidsträckta stadsmiljöerna är att de inte naturligt erbjuder sådana möjligheter. Därför planeras att i stadsmiljöer spara restområden, restaurera eller i vissa fall skapa helt nya biotoper och naturlika miljöer. En fråga som är viktig att ställa är om det är komplikationsfritt att lämna, återskapa eller rent av nyskapa skogs-, ängs- och våtmarksmiljöer i urbana områden. Tillsammans med pågående och framtida förändringar i klimatet kan dessa områden bli problemområden för olika sjukdomar som orsakas av exempelvis mygg och fästingburna smittämnen. Min utgångspunkt har varit att studera förekomst av fästingburna infektioner vid Isbladskärret, en populär skogs-, ängs- och våtmarksmiljö i Stockholm, och om enkla åtgärder kan minska smittrisken. I arbetets första del har jag studerat och beskriver fästingens ekologi för att sedan använda kunskapen i gestaltnings- och skötselförslaget för Isbladskärret. I arbetet undersöks även om fästingburna sjukdomar som Borrelia, TBE och Rickettsia helvetica förekommer i etablerade skogs-, ängs- och våtmarksmiljöer i urbana områden och i sådant fall i vilken utsträckning. Därför utfördes en insamling av fästingar vid Isbladskärret som beskrivs i del två. Fästingarna analyserades för olika smittämnen vid Zoonosis Science Center i Uppsala. Flera av fästingarna var smittade av Borrelia men varken TBE eller Rickettsia helvetica kunde hittas i de insamlade fästingarna. I del två har jag även undersökt i vilken utsträckning människor är medvetna och agerar utifrån eventuella hälsorisker kopplade till fästingar. Sammantaget gav mina litteraturstudier och de fynd av Borrelia som gjordes i fästingarna en bas för och fingervisning om hur de preventiva åtgärderna bör utföras. Slutligen undersöktes i den tredje och sista delen (med bakgrund från litteraturstudien och studien vid Isbladskärret) vilka möjligheter det via gestaltning och skötsel av skogs-, ängs- och våtmarksmiljöer i urbana områden finns att minska risken att människor drabbas av fästingburna sjukdomar. Baserat på detta har jag arbetat fram tre olika förslag på gestaltning och skötsel av området vid Isbladskärret som kan kategoriseras som små, medelstora och slutligen radikala åtgärder. Min förhoppning är att det här arbetet skall vara en viktig länk i kunskapskedjan kring hur olika åtgärder kan minimera risken för att utsättas för smittor vid besök i natur- och naturlika miljöer i urbana områden. Dessutom är det en strävan efter att skapa ett viktigt argument i diskursen om och i vilken omfattning vi som landskapsarkitekter måste lära oss att tänka preventivt. Inte bara när det gäller exempelvis fallolyckor men även kring så abstrakta ting som infektionssjukdomar.A growing and more demanding middle class in urban areas will pose challenges for the future. I have noted that urban people often are engaged in outdoor activities, such as running, forest walks, skiing and in some cases more specific interests such as studies of plants, insects or birds. The problem with the vast urban environments is that they do not naturally provide the study of plants, insects or birds. Therefore it is often planned to save, restore or in some cases create new habitats and nature like environments in urban areas. An important question when doing this is if there are complications when recreating or creating new forest, meadow and wetland habitats in urban areas. Together with ongoing and future changes in the climate, these areas can become problem areas for various diseases caused by, for example, mosquito and tick-borne pathogens. My starting point was to study the prevalence of tick-borne infections around Isbladskärret, a popular forest, meadow and wetland environment in Stockholm, and if simple measures can reduce infection risks. In the first part of the work I have studied and described the tick’s ecology in order to use the knowledge for the design- and management proposal at Isbladskärret. In this paper I have also examined if tick-borne diseases such as Lyme disease, TBE, and Rickettsia helvetica are prevalent in established forest, meadow and wetland habitats in urban areas, and if so to what extent. To answer this I collected ticks around Isbladskärret, which is described in part two. The ticks were analyzed for different pathogens in a laboratory located at Zoonosis Science Center in Uppsala. Several of the ticks were infected with Borrelia but neither TBE nor Rickettsia helvetica were found in the collected ticks. In part two, I have also examined people’s awareness and how they behave when they visit nature and natural environments. Overall, the literature study and the field study gave a direction about how preventive measures that would be advocated. In the third and final part I investigated (with the background of the literature study and the study at Isbladskärret) what opportunities, through design and management of forest, meadow and wetland habitats in urban areas, there are to reduce the exposure risk for people visiting the areas. Based on this I have worked out three different design- and management proposals for the area. These proposals can be categorized as the minimum, the middle way and finally the radical measures. I wish that this work will be an important link in the chain of knowledge about how various measures can minimize the risk of being exposed to infections while visiting nature and natural environments in urban areas. Moreover, this paper is an effort to create an important argument in the discourse about if and to what extent we as landscape architects need to think preventively. Not only in terms of for example fall accidents, but also on such abstract things as infectious diseases

Electrostatic potentials in the downward auroral current region

[1] Assuming a fixed ion density, adiabatic electron motion, and quasi-neutrality, we use the stationary Vlasov equation to derive the self-consistent potential in an auroral flux tube that carries downward current. Our model predicts downward electric fields $5 mV/m at an altitude near 2000 km, and around 4000 km the potential reaches$2.5 kV. A weak upward electric field at high altitudes reduces the potential, and the potential difference between the ionosphere and magnetosphere is much smaller. Citation: Vedin, J., and K

Människor och mönster

Mönster i markbeläggning är en av många faktorer som påverkar människors upplevelse av den omkringliggande miljön, och vi som landskapsarkitekter har ett stort ansvar i skapandet av dessa miljöer. Det vore rimligt om vår kunskap motsvarade vår inblandning i detta skapande, vilket vi inte tycker att det gör idag. Uppsatsen är främst baserad på litteraturstudier, intervjuer och en enkätundersökning. Dess huvudsakliga del berör människors psykologiska- och fysiologiska uppfattning av mönster i markbeläggning men uppsatsen behandlar även geometriska mönster och markbeläggningens utveckling över tid i Sverige, samt matematikens betydelse för arkitekturen. Det finns inte mycket forskning om hur människor upplever mönster i markbeläggning, men faktum är att mönster påverkar oss från dagen då vi föds. Mönster kan få oss att känna lugn och tillit eller otrygghet och stress. Att gestalta väl med mönster är en balansgång mellan överstimulans och monotoni. Några påstår till och med att en väl genomtänkt miljö, inklusive dess markbeläggning, kan minska vandalism och drogbehov samt bidra till ett socialt och välfungerande samhälle. En av de sista och viktigaste delarna i uppsatsen består av en sammanställning av en enkätundersökning i vilken fotografier av olika markbeläggningar presenterades tillsammans med frågor om hur dessa upplevs. Resultatet av undersökningen ger ett smakprov på hur en mer omfattande studie av liknande slag skulle kunna öka våra kunskaper kring människors upplevelse av mönster i markbeläggning och är således en viktig del av uppsatsen. Vi konstaterar att olika sorters markbeläggningar påverkar människors upplevelse på olika sätt. Uppsatsen är ett försök till att uppmuntra en debatt om hur landskapsarkitekter kan designa väl, på ett professionellt sätt, och med vetenskapliga belägg vid gestaltning med mönster i markbeläggning. Ämnet är aktuellt och borde belysas ytterligare såväl inom vår yrkeskår som inom andra.Patterns of paving stones are one of many factors that affect people’s experience of the surrounding environment. As landscape architects we have a great responsibility in designing/creating these surroundings and it would seem reasonable that our knowledge should reflect our involvement in this process, which we do not think it does today. This thesis is mainly based on literature studies, interviews and a questionnaire. Its main focus regards people’s psychological and physiological experience of patterns of paving stones. The thesis also touches on how geometrical and paving stone patterns have developed over time, and what this mathematically means to architecture. There is not a lot of research about patterns of paving stones related to people’s experiences, but the fact is, humans are affected by patterns from the day they were born. Patterns can make us feel calm and safe, or insecure and stressed. To design well with patterns is a fine balance between over stimulation and monotony. Some claim that a consciously designed environment, including its patterns of paving stones, can decrease vandalism and drug use, and contribute to a social and well functioning society. One of the last, and most important parts of the thesis contains a summary of a questionnaire where a variety of people answered questions about how they, whilst provided photos of patterns of paving stones, experienced them. The result is an important indicator of how more extensive studies could enrich our knowledge of people’s experience of patterns of paving stones, and is due to the lack of this information today, a significant part of this thesis. In this thesis we conclude that different types of paving stones affect people´s experiences in different ways. The thesis is an attempt to encourage a debate on how landscape architects can use patterns to design well, in a professional way and with scientific reasoning. The subject is relevant and deserves attention in our profession as well as in others

Enhancement of electric and magnetic wave fields at density gradients

We use Freja satellite data to investigate irregular small-scale density variations. The observations are made in the auroral region at about 1000-1700 km. The density variations are a few percent, and the structures are found to be spatial down to a scale length of a few ion gyroradii. Irregular density variations are often found in an environment of whistler mode/lower hybrid waves and we show that at the density gradients both the electric and magnetic wave fields are enhanced

Cascade and Damping of Alfv\'{e}n-Cyclotron Fluctuations: Application to Solar Wind Turbulence Spectrum

With the diffusion approximation, we study the cascade and damping of Alfv\'{e}n-cyclotron fluctuations in solar plasmas numerically. Motivated by wave-wave couplings and nonlinear effects, we test several forms of the diffusion tensor. For a general locally anisotropic and inhomogeneous diffusion tensor in the wave vector space, the turbulence spectrum in the inertial range can be fitted with power-laws with the power-law index varying with the wave propagation direction. For several locally isotropic but inhomogeneous diffusion coefficients, the steady-state turbulence spectra are nearly isotropic in the absence of damping and can be fitted by a single power-law function. However, the energy flux is strongly polarized due to the inhomogeneity that leads to an anisotropic cascade. Including the anisotropic thermal damping, the turbulence spectrum cuts off at the wave numbers, where the damping rates become comparable to the cascade rates. The combined anisotropic effects of cascade and damping make this cutoff wave number dependent on the wave propagation direction, and the propagation direction integrated turbulence spectrum resembles a broken power-law, which cuts off at the maximum of the cutoff wave numbers or the $^4$He cyclotron frequency. Taking into account the Doppler effects, the model can naturally reproduce the broken power-law wave spectra observed in the solar wind and predicts that a higher break frequency is aways accompanied with a greater spectral index change that may be caused by the increase of the Alfv\'{e}n Mach number, the reciprocal of the plasma beta, and/or the angle between the solar wind velocity and the mean magnetic field. These predictions can be tested by future observations

Modulation of NTC frequencies by Pc5 ULF pulsations : experimental test of the generation mechanism and magnetoseismology of the emitting surface

Nonthermal continuum (NTC) radiation is believed to be emitted by the conversion of an electrostatic wave into an electromagnetic one, which takes place at the Earth's magnetic equator. It is generally accepted that the frequency of the electrostatic wave at the source meets a local characteristic frequency placed in between two multiples of the electron cyclotron frequency, fce, which results in emission of a narrow band frequency element. In an event on 14 August 2003, we compare oscillations of the central frequency of distinct NTC frequency elements observed from Cluster orbiting near perigee, with simultaneous Pc5 Ultra Low Frequency (ULF) pulsations in the magnetic field observed from the same platform. The latter magnetic perturbations are interpreted as magnetohydrodynamic poloidal waves, where fundamental and second harmonic modes coexist. The NTC oscillation and the fundamental wave have similar periods, but are phase shifted by a quarter of period. From the correlation between both signals, and the proximity of the NTC source (localized via triangulation) with Cluster, we infer that the poloidal perturbations are spatially uniform between the source and the satellites. From the phase shift between signals, we conclude that the electrostatic wave which converts into NTC is mainly governed by the plasma density, affected by movements of the magnetic field lines. Furthermore, we demonstrate that the observations can be used to perform a magnetoseismology of the emitting surface. The results show a steepening of the plasmapause density profile near the satellites, which can be responsible for the generation of NTC emission

Trapping and acceleration of upflowing ionospheric electrons in the magnetosphere by electrostatic electron cyclotron harmonic (ECH) waves

During geomagnetically active conditions upflowing field-aligned electrons which form part of the Birkland current system have been observed at energies of up to 100 eV. If the first adiabatic invariant is conserved these electrons would reach the conjugate ionosphere without trapping in the magnetosphere. Here we show, by using quasi-linear diffusion theory, that electrostatic electron cyclotron harmonic (ECH) waves can diffuse these low energy electrons in pitch angle via Doppler shifted cyclotronresonance and trap them in the magnetosphere. We show that energy diffusion is comparable to pitch angle diffusion up to energies of a few keV. We suggest that ECH waves trap ionospheric electrons in the magnetosphere and accelerate them to produce butterfly pitch-angle distributions at energies of up to a few keV. We suggest that ECH waves play a role in magnetosphere-ionosphere coupling and help provide the source electron population for the radiation belts