Compensation between resolved wave driving and parameterized orographic gravity wave driving of the Brewer–Dobson circulation and its response to climate change

Following recent findings, the interaction between resolved (Rossby) wave drag and parameterized orographic gravity wave drag (OGWD) is investigated, in terms of their driving of the Brewer–Dobson circulation (BDC), in a comprehensive climate model. To this end, the parameter that effectively determines the strength of OGWD in present-day and doubled CO2 simulations is varied. The authors focus on the Northern Hemisphere during winter when the largest response of the BDC to climate change is predicted to occur. It is found that increases in OGWD are to a remarkable degree compensated by a reduction in midlatitude resolved wave drag, thereby reducing the impact of changes in OGWD on the BDC. This compensation is also found for the response to climate change: changes in the OGWD contribution to the BDC response to climate change are compensated by opposite changes in the resolved wave drag contribution to the BDC response to climate change, thereby reducing the impact of changes in OGWD on the BDC response to climate change. By contrast, compensation does not occur at northern high latitudes, where resolved wave driving and the associated downwelling increase with increasing OGWD, both for the present-day climate and the response to climate change. These findings raise confidence in the credibility of climate model projections of the strengthened BDC.

Thermospheric Control of the Auroral Source of O+Ions for the Magnetosphere

Linear theory, model ion-density profiles and MSIS neutral thermospheric predictions are used to investigate the stability of the auroral, topside ionosphere to oxygen cyclotron waves: variations of the critical height, above which the plasma is unstable, with field-aligned current, thermal ion density and exospheric temperature are considered. In addition, probabilities are assessed that interactions with neutral atomic gases prevent O+ ions from escaping into the magnetosphere after they have been transversely accelerated by these waves. The two studies are combined to give a rough estimate of the total O+ escape flux as a function of the field-aligned current density for an assumed rise in the perpendicular ion temperature. Charge exchange with neutral oxygen, not hydrogen, is shown to be the principle limitation to the escape of O+ ions, which occurs when the waves are driven unstable down to low altitudes. It is found that the largest observed field-aligned current densities can heat a maximum of about 5×1014 O+ ions m−2 to a threshold above which they are subsequently able to escape into the magnetosphere in the following 500s. Averaged over this period, this would constitute a flux of 1012 m−2 s−1 and in steady-state the peak outflow would then be limited to about 1013 m−2 s−1 by frictional drag on thermal O+ at lower altitudes. Maximum escape is at low plasma density unless the O+ scale height is very large. The outflow decreases with decreasing field-aligned current density and, to a lesser extent, with increasing exospheric temperature. Upward flowing ion events are evaluated as a source of O+ ions for the magnetosphere and as an explanation of the observed solar cycle variation of ring current O+ abundance.

Field-aligned plasma flow in the quiet, mid-latitude ionosphere deduced from topside soundings

A method for quantifying diffusive flows of O+ ions in the topside ionosphere from satellite soundings is described. A departure from diffusive equilibrium alters the shape of the plasma scale-height profile near the F2-peak where ion-neutral frictional drag is large. The effect enables the evaluation of , the field-aligned flux of O+ ions relative to the neutral oxygen atom gas, using MSIS model values for the neutral thermospheric densities and temperature. Upward flow values are accurate to within about 10%, the largest sources of error being the MSIS prediction for the concentration of oxygen atoms and the plasma temperature gradient deduced from the sounding. Downward flux values are only determined to within 20%. From 60,000 topside soundings, taken at the minimum and rising phase of the solar cycle, a total of 1098 mean scale-height profiles are identified for which no storm sudden commencement had occurred in the previous 12 days and for which Kp was less than 2o, each mean profile being an average of about six soundings. A statistical study ofdeduced from these profiles shows the diurnal cycle of O+ flow in the quiet, topside ionosphere at mid-latitudes and its seasonal variations. The differences betweenand ion flux observations from incoherent scatter radars are considered using the meridional thermospheric winds predicted by a global, three-dimensional model. The mean interhemispheric flow from summer to winter is compared with predictions by a numerical model of the protonospheric coupling of conjugate ionospheres for up to 6 days following a geomagnetic storm. The observed mean (of order 3 × 1016 ions day−1 along a flux tube of area 1 m2 at 1000 km) is larger than predicted for day 6 and the suggested explanation is a decrease in upward flows from the winter, daytime ionosphere between the sixth and twelfth days.

Departures from diffusive equilibrium in the topside F-layer from satellite soundings

A method for the detection of O+ ion fluxes from topside soundings is described. The shape of the plasma scale-height profile is altered by such flows only at heights near the F2-peak, where ion-neutral drag is large. Model profiles are used to relate changes in scale height to the ratio (φ/φL) where φ is the field-aligned O+ flux (relative to the neutral air) and φL is the limiting value set by frictional drag. Values of (φ/φL) can then be determined to within a few per cent from experimental soundings, using the plasma temperature and its gradient (as deduced from the observed profile) and the MSIS model neutral temperature. It was found that 3700 topside profiles show departures from diffusive equilibrium, out of 10,000 used to obtain the global morphology of (φ/φL) near the sunspot minimum. Results reveal dynamic ion-flow effects such as the transequatorial breeze and the effects of the polar wind and protonospheric replenishment light-ion flows can be inferred.

Validation of a priori CME arrival predictions made using real-time heliospheric imager observations

Between December 2010 and March 2013, volunteers for the Solar Stormwatch (SSW) Citizen Science project have identified and analyzed coronal mass ejections (CMEs) in the near real-time Solar Terrestrial Relations Observatory Heliospheric Imager observations, in order to make “Fearless Forecasts” of CME arrival times and speeds at Earth. Of the 60 predictions of Earth-directed CMEs, 20 resulted in an identifiable Interplanetary CME (ICME) at Earth within 1.5–6 days, with an average error in predicted transit time of 22 h, and average transit time of 82.3 h. The average error in predicting arrival speed is 151 km s−1, with an average arrival speed of 425km s−1. In the same time period, there were 44 CMEs for which there are no corresponding SSW predictions, and there were 600 days on which there was neither a CME predicted nor observed. A number of metrics show that the SSW predictions do have useful forecast skill; however, there is still much room for improvement. We investigate potential improvements by using SSW inputs in three models of ICME propagation: two of constant acceleration and one of aerodynamic drag. We find that taking account of interplanetary acceleration can improve the average errors of transit time to 19 h and arrival speed to 77 km s−1.

Improving a global model from the boundary layer: total turbulent energy and the neutral limit Prandtl number

Model intercomparisons have identified important deficits in the representation of the stable boundary layer by turbulence parametrizations used in current weather and climate models. However, detrimental impacts of more realistic schemes on the large-scale flow have hindered progress in this area. Here we implement a total turbulent energy scheme into the climate model ECHAM6. The total turbulent energy scheme considers the effects of Earth’s rotation and static stability on the turbulence length scale. In contrast to the previously used turbulence scheme, the TTE scheme also implicitly represents entrainment flux in a dry convective boundary layer. Reducing the previously exaggerated surface drag in stable boundary layers indeed causes an increase in southern hemispheric zonal winds and large-scale pressure gradients beyond observed values. These biases can be largely removed by increasing the parametrized orographic drag. Reducing the neutral limit turbulent Prandtl number warms and moistens low-latitude boundary layers and acts to reduce longstanding radiation biases in the stratocumulus regions, the Southern Ocean and the equatorial cold tongue that are common to many climate models.

Revisiting the ‘Venturi effect’ in passage ventilation between two non-parallel buildings

A recent study conducted by Blocken et al. (Numerical study on the existence of the Venturi effect in passages between perpendicular buildings. Journal of Engineering Mechanics, 2008,134: 1021-1028) challenged the popular view of the existence of the ‘Venturi effect’ in building passages as the wind is exposed to an open boundary. The present research extends the work of Blocken et al. (2008a) into a more general setup with the building orientation varying from 0° to 180° using CFD simulations. Our results reveal that the passage flow is mainly determined by the combination of corner streams. It is also shown that converging passages have a higher wind-blocking effect compared to diverging passages, explained by a lower wind speed and higher drag coefficient. Fluxes on the top plane of the passage volume reverse from outflow to inflow in the cases of α=135°, 150° and 165°. A simple mathematical expression to explain the relationship between the flux ratio and the geometric parameters has been developed to aid wind design in an urban neighborhood. In addition, a converging passage with α=15° is recommended for urban wind design in cold and temperate climates since the passage flow changes smoothly and a relatively lower wind speed is expected compared with that where there are no buildings. While for the high-density urban area in (sub)tropical climates such as Hong Kong where there is a desire for more wind, a diverging passage with α=150° is a better choice to promote ventilation at the pedestrian level.

Sensitivity and variability redux in hot-Jupiter flow simulations

We revisit the issue of sensitivity to initial flow and intrinsic variability in hot-Jupiter atmospheric flow simulations, originally investigated by Cho et al. (2008) and Thrastarson & Cho (2010). The flow in the lower region (~1 to 20 MPa) `dragged' to immobility and uniform temperature on a very short timescale, as in Liu & Showman (2013), leads to effectively a complete cessation of variability as well as sensitivity in three-dimensional (3D) simulations with traditional primitive equations. Such momentum (Rayleigh) and thermal (Newtonian) drags are, however, ad hoc for 3D giant planet simulations. For 3D hot-Jupiter simulations, which typically already employ strong Newtonian drag in the upper region, sensitivity is not quenched if only the Newtonian drag is applied in the lower region, without the strong Rayleigh drag: in general, both sensitivity and variability persist if the two drags are not applied concurrently in the lower region. However, even when the drags are applied concurrently, vertically-propagating planetary waves give rise to significant variability in the ~0.05 to 0.5 MPa region, if the vertical resolution of the lower region is increased (e.g. here with 1000 layers for the entire domain). New observations on the effects of the physical setup and model convergence in ‘deep’ atmosphere simulations are also presented.

The impact of variable sea ice roughness on changes in Arctic Ocean surface stress: a model study

The Arctic sea ice cover is thinning and retreating, causing changes in surface roughness that in turn modify the momentum flux from the atmosphere through the ice into the ocean. New model simulations comprising variable sea ice drag coefficients for both the air and water interface demonstrate that the heterogeneity in sea ice surface roughness significantly impacts the spatial distribution and trends of ocean surface stress during the last decades. Simulations with constant sea ice drag coefficients as used in most climate models show an increase in annual mean ocean surface stress (0.003 N/m2 per decade, 4.6%) due to the reduction of ice thickness leading to a weakening of the ice and accelerated ice drift. In contrast, with variable drag coefficients our simulations show annual mean ocean surface stress is declining at a rate of -0.002 N/m2 per decade (3.1%) over the period 1980-2013 because of a significant reduction in surface roughness associated with an increasingly thinner and younger sea ice cover. The effectiveness of sea ice in transferring momentum does not only depend on its resistive strength against the wind forcing but is also set by its top and bottom surface roughness varying with ice types and ice conditions. This reveals the need to account for sea ice surface roughness variations in climate simulations in order to correctly represent the implications of sea ice loss under global warming.

Processes controlling surface, bottom and lateral melt of Arctic sea ice in a state of the art sea ice model

We present a modelling study of processes controlling the summer melt of the Arctic sea ice cover. We perform a sensitivity study and focus our interest on the thermodynamics at the ice–atmosphere and ice–ocean interfaces. We use the Los Alamos community sea ice model CICE, and additionally implement and test three new parametrization schemes: (i) a prognostic mixed layer; (ii) a three equation boundary condition for the salt and heat flux at the ice–ocean interface; and (iii) a new lateral melt parametrization. Recent additions to the CICE model are also tested, including explicit melt ponds, a form drag parametrization and a halodynamic brine drainage scheme. The various sea ice parametrizations tested in this sensitivity study introduce a wide spread in the simulated sea ice characteristics. For each simulation, the total melt is decomposed into its surface, bottom and lateral melt components to assess the processes driving melt and how this varies regionally and temporally. Because this study quantifies the relative importance of several processes in driving the summer melt of sea ice, this work can serve as a guide for future research priorities.

SIMULATIONS OF WINDS OF WEAK-LINED T TAURI STARS: THE MAGNETIC FIELD GEOMETRY AND THE INFLUENCE OF THE WIND ON GIANT PLANET MIGRATION

By means of numerical simulations, we investigate magnetized stellar winds of pre-main-sequence stars. In particular, we analyze under which circumstances these stars will present elongated magnetic features (e.g., helmet streamers, slingshot prominences, etc). We focus on weak-lined T Tauri stars, as the presence of the tenuous accretion disk is not expected to have strong influence on the structure of the stellar wind. We show that the plasma-beta parameter (the ratio of thermal to magnetic energy densities) is a decisive factor in defining the magnetic configuration of the stellar wind. Using initial parameters within the observed range for these stars, we show that the coronal magnetic field configuration can vary between a dipole-like configuration and a configuration with strong collimated polar lines and closed streamers at the equator (multicomponent configuration for the magnetic field). We show that elongated magnetic features will only be present if the plasma-beta parameter at the coronal base is beta(0) << 1. Using our self-consistent three-dimensional magnetohydrodynamics model, we estimate for these stellar winds the timescale of planet migration due to drag forces exerted by the stellar wind on a hot-Jupiter. In contrast to the findings of Lovelace et al., who estimated such timescales using the Weber and Davis model, our model suggests that the stellar wind of these multicomponent coronae are not expected to have significant influence on hot-Jupiters migration. Further simulations are necessary to investigate this result under more intense surface magnetic field strengths (similar to 2-3 kG) and higher coronal base densities, as well as in a tilted stellar magnetosphere.

Molecular Ordering in Layer-by-Layer Polyelectrolyte Films Studied by Sum-Frequency Vibrational Spectroscopy: The Effects of Drying Procedures

Sum-Frequency Vibrational Spectroscopy (SFVS) has been used to investigate the effect of nitrogen-flow drying on the molecular ordering of Layer-by-Layer (LbL) films of poly(allylamine hydrochloride) (PAH) alternated with poly(styrene sulfonate) (PSS). We find that films dried by spontaneous water evaporation are more ordered and homogeneous than films dried by nitrogen flow. The latter are quite inhomogeneous and may have regions with highly disordered polymer conformation. We propose that drying by spontaneous water evaporation reduces the effect of drag by the drying front, while during nitrogen-flow drying the fast evaporation of water ""freezes"" the disordered conformation of adsorbed polyelectrolyte molecules. These findings are important for many applications of LbL films, since device performance usually depends on film morphology and its molecular structure.

Systemförvaltning hos Banverket – design av gemensam process för ändringshantering

Vår uppdragsgivare för detta arbete var IT-avdelningen på Banverkets huvudkontor. Deras upp-drag till oss var att kartlägga nuläget i ändringshanteringen i systemförvaltningen. Utifrån den kartläggningen skulle vi även utveckla en gemensam process med tillhörande processbeskrivning för ändringshanteringen. Ändringshantering är alla de aktiviteter som uppstår från det att ett förändringsbehov inkommer till dess att förändringen är införd. Banverket har under 2003 arbetat fram en metodik för systemförvaltning, som fortfarande är under utveckling. Metodikens stöd för det operativa arbetet, i synnerhet ändringshanteringen, är inte tillräcklig. Förvaltningsledare har hittills skapat sina egna processer kring hur ändringshan-teringen ska gå till och de finns inte dokumenterade, utan existerar som enskild kunskap. Detta leder till att systemförvaltningen blir personbunden och konsekvensen blir bland annat att det är resurskrävande att byta ut personen i förvaltningen samt att det tar längre tid vid överlämning av förvaltningen till ny person. Vi genomförde semistrukturerade intervjuer med nio systemförvaltare och förvaltningsledare för att kunna beskriva deras arbetssätt i nuläget. Till hjälp i beskrivningen av arbetssättet använde vi handlingsgrafer enligt metoden FA/SIM. Med handlingsgraferna kunde vi jämföra de olika arbetssätten. Vid jämförelsen kunde vi se att det fanns ett antal handlingar som är återkommande i de flesta nulägesbeskrivningarna. Vi analyserade dessa handlingar med hjälp av affärsaktsteorin för att få svar på om ändringshanteringen är affärstydlig. Vi kunde se att förvaltningsledarna saknar ett bra stöd för vilken information som bör komma in med varje förändringsbehov. Detta leder till att förvaltningsledaren känner en osäkerhet i om den prioriterat rätt och kan leda till att han/hon hamnar i ett underläge i en eventuell förhandling med leverantören. I acceptanstestningen märkte vi att den inte utförs på ett strukturerat sätt samt att det finns en tendens till att förvaltningsledaren i vissa fall förlitar sig på den testning leverantören utför. Den ändringshanteringsprocess vi utvecklat är en grund till ett gemensamt arbetssätt, men en viss fördjupning av detaljnivån i processen måste ske mot varje förvaltningsobjekt. Vi menar att för att säkerställa att rätt och jämförbar information om de olika förändringsbehoven kommer in behöver förvaltningsledaren arbeta fram någon form av frågemall. Genom att genomföra en nyt-tovärdering enligt PENG-modellen tror vi att förvaltningsledaren hittar de frågor som han/hon behöver ha svar på i prioriteringsfasen och som bör ingå i frågemallen. Acceptanstestningen bör ske på ett strukturerat sätt och vi föreslår att förvaltningsledaren arbetar fram ett testprotokoll för sitt förvaltningsobjekt samt identifierar några för verksamheten kritiska funktionaliteter som också bör ingå i testprotokollet.

Modell för att utvärdera spänningar vid reducervalsning

Ovako Steel AB i Hofors tillverkar varmvalsade rör. Ett av de sista stegen i tillverkningsprocessen är en konventionell valsning i ett antal valspar kallad reducervalsning. De valsade rören uppvisar ibland en ojämn väggtjocklek längs rörlängden på grund av att det uppstår drag- och tryckspänningar i rören mellan valsparen. Syftet med examensarbetet är att öka kunskapen om dessa spänningars inverkan på det färdiga röret samt ge förslag på hur processen kan förbättras. I examensarbetet har undersökts vilka parametrar som påverkar spänningarna i valsningsprocessen. Detta har utförts genom att skapa en teoretisk modell för valsning utan drag- och tryckspänningar som sedan jämförs med uppmätta data från sju provade rör med olika mått och materialtyper. Försök har även utförts genom att variera valsmotorernas hastigheter för att inducera drag- och tryckspänningar i rören. Resultatet visar att spänningarna påverkas av rörens reduktion, valsarnas hastighetsökning, materialtyp och antal valsar i valsserien. Valsarnas styrning medför att spänningsfri valsning endast kan erhållas genom att förändra rörets reduktion i valsarna. Resultaten visar även att valsarnas motorhastighet kan användas för att motverka de spänningar som uppstår under valsningsprocessen.

Genusperspektiv i historieläromedel - finns det? : En jämförande analys av fem läroböcker i historia för gymnasiet utgivna under åren 1995-2004

Syftet med denna uppsats har varit att studera om det finns något genusperspektiv i valda nedslag i gymnasieläroböcker i ämnet historia. De teoretiska utgångspunkterna och definitionerna har hämtats i Micael Nilssons rapport Historia ur ett genusperspektiv – En granskning av genusaspekterna i ämnet historia vid Linköpings universitet. Materialet har kategoriserats i tre olika perspektiv; kvinnohi-storiskt perspektiv, jämställdhetsperspektiv och genusperspektiv. Litteraturen har därefter place-rats i den så kallade genustrappan som i Nilsson version består av fem olika steg; genusmedveten, jämställdhetsmedveten, könsmedveten, könsomedveten eller könsmakts-förstärkande. Det un-dersökta materialet har bestått av fem läroböcker som behandlar A-kursen i historia. Läroböcker-na är utgivna på fem olika förlag, ingen av dem har en ensam författare och tre av böckerna har en kvinnlig medförfattare. Undersökningen är baserad på både den kvalitativa och den kvantitati-va metoden. Den kvantitativa delen av undersökning har gått ut på att räkna antal kvinnonamn i böckernas register och antal illustrationer som innehåller kvinnor. I den kvalitativa delen av un-dersökningen har material om kvinnor samt kvinnors situation i kapitlen om antikens Grekland, nordisk medeltid och industrialismen analyserats. Undersökningen visar att läroböckerna repre-senterar en historieskrivning som i stora drag lämnar kvinnorna utanför. Ingen av böckerna når upp till kategorien genusmedveten, de två böcker som placerar sig högst når kategorien jäm-ställdhetsmedveten. Resultatet visar att läroböckerna inte lever upp till styrdokumentens krav på en jämställd undervisning.