A turbulence-driven model for heating and acceleration of the fast wind in coronal holes

A model is presented for generation of fast solar wind in coronal holes, relying on heating that is dominated by turbulent dissipation of MHD fluctuations transported upwards in the solar atmosphere. Scale-separated transport equations include large-scale fields, transverse Alfvenic fluctuations, and a small compressive dissipation due to parallel shears near the transition region. The model accounts for proton temperature, density, wind speed, and fluctuation amplitude as observed in remote sensing and in situ satellite data.Comment: accepted for publication in ApJ

Building a professional global disaster response team at an academic health-care institution: the professionalisation of humanitarian health-care workers

AbstractBackgroundThe numbers of individuals affected by disasters and conflict are on the rise, similarly are the numbers of clinicans who seek to help. Although health-care workers want to provide immediate clinical care—as in field hospitals—disaster response requires a comprehensive set of knowledge, skills, and behaviour not taught in medical and nursing schools. With competency-based training and a vetted and credentialed workforce, academic medical institutions have the opportunity to augment emergency response for humanitiarian aid organisations. We aim to describe the minimum standards for building a professional disaster response team within an academic medical institution.MethodsThrough literature review and key informant interviews, we built a database to describe emergency response experience in 21 countries within 25 national and international aid organisations, governments, and academic universities. We created a checklist and applied this to responses for sudden onset and chronic crises. Key variables included deployment parameters, credentialing procedures, competency or skillset requirements, predeployment and postdeployment preparation, and types of organisational support.FindingsWe found large variation between organisations for emergency response, including the credentialling process, definition of competency or skillsets, implementation of deployment, and the extent of organisational support. From this analysis, we created a set of minimum standards for deployment, including physical and mental fitness, previous professional experience, team-based response, appropriate flexible skillset, approval or vetting by direct supervisors, initial or duration of availability, cultural or language competency, self reliance in austere conditions, communication skills, briefing and debriefing participation, and support from organisation.InterpretationMinimum standards and guidelines for institutions deploying health-care workers to disasters is a key step in professionalisation.FundingNone

Empirical Constraints on Proton and Electron Heating in the Fast Solar Wind

We analyze measured proton and electron temperatures in the high-speed solar wind in order to calculate the separate rates of heat deposition for protons and electrons. When comparing with other regions of the heliosphere, the fast solar wind has the lowest density and the least frequent Coulomb collisions. This makes the fast wind an optimal testing ground for studies of collisionless kinetic processes associated with the dissipation of plasma turbulence. Data from the Helios and Ulysses plasma instruments were collected to determine mean radial trends in the temperatures and the electron heat conduction flux between 0.29 and 5.4 AU. The derived heating rates apply specifically for these mean plasma properties and not for the full range of measured values around the mean. We found that the protons receive about 60% of the total plasma heating in the inner heliosphere, and that this fraction increases to approximately 80% by the orbit of Jupiter. A major factor affecting the uncertainty in this fraction is the uncertainty in the measured radial gradient of the electron heat conduction flux. The empirically derived partitioning of heat between protons and electrons is in rough agreement with theoretical predictions from a model of linear Vlasov wave damping. For a modeled power spectrum consisting only of Alfvenic fluctuations, the best agreement was found for a distribution of wavenumber vectors that evolves toward isotropy as distance increases.Comment: 11 pages (emulateapj style), 5 figures, ApJ, in pres

Improved Constraints on the Preferential Heating and Acceleration of Oxygen Ions in the Extended Solar Corona

We present a detailed analysis of oxygen ion velocity distributions in the extended solar corona, based on observations made with the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO spacecraft. Polar coronal holes at solar minimum are known to exhibit broad line widths and unusual intensity ratios of the O VI 1032, 1037 emission line doublet. The traditional interpretation of these features has been that oxygen ions have a strong temperature anisotropy, with the temperature perpendicular to the magnetic field being much larger than the temperature parallel to the field. However, recent work by Raouafi and Solanki suggested that it may be possible to model the observations using an isotropic velocity distribution. In this paper we analyze an expanded data set to show that the original interpretation of an anisotropic distribution is the only one that is fully consistent with the observations. It is necessary to search the full range of ion plasma parameters to determine the values with the highest probability of agreement with the UVCS data. The derived ion outflow speeds and perpendicular kinetic temperatures are consistent with earlier results, and there continues to be strong evidence for preferential ion heating and acceleration with respect to hydrogen. At heliocentric heights above 2.1 solar radii, every UVCS data point is more consistent with an anisotropic distribution than with an isotropic distribution. At heights above 3 solar radii, the exact probability of isotropy depends on the electron density chosen to simulate the line-of-sight distribution of O VI emissivity. (abridged abstract)Comment: 19 pages (emulateapj style), 13 figures, ApJ, in press (v. 679; May 20, 2008