In this project warm extreme temperature events in the Arctic region during the spring months March, April and May were identified and analysed. In the analysis daily average NCEP reanalysis data from NOAA/OAR/ESRL PSL format was used. The extreme events were retrieved as the highest positive temperature anomalies from the climatological mean, and the synoptic scale plots for the 50 most extreme events were created to identify what patterns caused the extreme warming over the Polar region. By contouring the areas of statistical significance, the regions with a reoccuring pattern were identified. The results conclude that cyclonic activity over the high Arctic extending down over Greenland and northern Canada combined with anomalously high geopotential height over the north Pacific ocean, over the Arctic, and towards Siberia cause the high temperatures over the pole. A weaker Polar Vortex causes perturbations in the jet stream, ridges in these Rossby waves can act as a pathway for warm and moist air from the oceanic regions which has a warming effect in the Arctic. Further analysis can be done to investigate what teleconnections these spring-time extreme events have on a global scale. / Under detta projekt har extremt varma temperaturevent i Arktisområdet under vårmånaderna Mars, April och Maj identifierats samt analyserats, genom att använda daglig medelvärdes NCEP reanalys data från NOAA/OAR/ESRL PSL i NetCDF format. De extrema händelserna identifierades genom att ta de största positiva temperaturavvikelserna från ett klimatologiskt medelvärde, storskaliga avvikelseplottar skapades för de 50 mest extrema händelserna för att kunna identifiera meteorologiska mönster som ovanligt varma Arktisdagar. De områden med mest återkommande mönsterna var statistiskt signifikanta  och markerades med svarta konturer. Resultaten visar att lågtrycksaktivitet i Arktis som sträcker sig ner över Grönland samt norra Kanada kombinerat med höga geopotentialhöjdavvikelser över Stilla havet och Sibirien som sträcker sig upp mot Nordpolen orsakar ovanligt höga temperaturer i Arktis. En svag polarvirvel orsakar störningar i jetströmmen, dessa ryggar i jetströmmen kan transportera varm fuktig luft från haven mot polen vilket kan ha en värmande effekt. Vidare forskning kan utföras för att identifiera de exakta kopplingarna och konsekvenserna som dessa varma extrema Arktishändelser har globalt.

Jetströmmar betyder mycket för meteorologer och fungerar som ett hjälpmedel för prognostisering av lågtryck. Kvadrantmodellen för jetströmsstråk beskriver hur det kan bildas lågtryck och konvergens vid marknivå på olika sidor om jetströmmen. Jetströmmar är också av betydelse för flygtrafiken, eftersom man kan spara tid och bränsle genom att flyga in i – eller genom att inte flyga in i – en jetström. Det är känt att jetströmmar ibland kan ge upphov till klarluftsturbulens (CAT), och studier har visat att turbulensen ofta är associerade med stabilt stratifierade zoner i närheten av jetströmmen. Denna studie börjar med en teoridel där jetströmmars uppkomst och kvadrantmodellen redogörs. Teoridelen fortsätter med en kort beskrivning av hur jetströmmar påverkar flygtrafiken och vad det finns för system som varnar för farliga fenomen som är kopplade till jetströmmarna. Det tas även upp att flygturbulensen som upplevs av flygplan inte nödvändigtvis orsakas av termisk eller mekanisk turbulens, utan även kan orsakas av stående vågor. I arbetets senare del görs en fallstudie på två jetströmmar som gav upphov till kraftig flygturbulens under januari månad 2011. Från sonderingsdata beräknades Scorer-parametern och Richardsons tal för att se om dessa värden kunde relateras till flygturbulensen. Resultatet visade att Richardsons tal aldrig föll under 0.25 och antyder därför att det inte fanns någon fullt utvecklad turbulens. Vågor i luften kan därför vara en förklaring till flygturbulensen. Resultatet visade också att Scorer-parametern antog lokala minima och hade tydligare relation till flygturbulensen än Richardsons tal vad gäller flygturbulensens position i höjdled. / Jet streams are useful as a tool for meteorologist to make forecasts of low pressure areas. The four quadrant model describing jet streaks reveals how lows and convergence could form over ground levels on different sides of a jet streak. Jet streams are also of great importance for the aviation industry, as one could save time and fuel by flying into – or by not flying into – a jet stream. It is known that the jet streams sometimes can induce Clear Air Turbulence (CAT), and studies have shown that the turbulence is often associated with stable stratified layers in the vicinity of the jet stream. This study starts with a theory section describing the cause of jet streams and the four quadrant model. The theory section continues with a description of why jet streams could be a hazard for airplanes, and also a description of existing reporting and warning systems that are used to prevent pilots from flying into dangerous phenomena. In this section, it is also emphasized that in-flight turbulence not necessarily is a result of thermal or mechanical turbulence, but could also be induced by standing waves in the atmosphere. The latter part of this report is a case study of two jet streaks that was the cause of severe in-flight turbulence in January 2011. The Scorer parameter and the Richardson number were computed using data from atmospheric soundings. The results show that the Richardson number never fell below 0.25, suggesting that there were no fully-developed turbulence. Waves in the air could therefore be an alternative explanation to the reported in-flight turbulence. The results also show that the Scorer parameter had local minima on the levels where the in-flight turbulence occurred. In contrast to this, the Richardson number had no apparent relation to the position of the reported turbulence.

Dynamic Systems Theory (DST) and spectral analysis are employed to study the tropospheric jet stream and the stratospheric polar vortex. The objective is to investigate the relationship between Rossby wave activity and inverse persistence and dimensionality of geopotential height at 250 hPa and 10 hPa, as these two dynamical indicators are expected to show a characteristic behavior of Rossby wave harmonics. The results show that persistent states exhibit suppressed Rossby wave activity for eastward-propagating Rossby waves, whereas it is increased for the westward counterpart. Positive anomalies of spectral power at positive phase speeds are present for less persistent states. Events with low dimensionality relate to the suppression of most Rossby waves, while an increase in spectral power is present during high dimensional states. The results were more pronounced in the stratosphere compared to the troposphere with different spatial patterns of geopotential height anomalies due to additional factors influencing the location of Rossby waves. Furthermore, Sudden Stratospheric Warmings (SSWs) are connected to a decrease in persistence up to 2 weeks prior, followed by a significant increase in persistence and dimensionality, and reduced integrated spectral power. Strong Polar Vortex events (SPVs) exhibit the opposite behavior with an increase in persistence before and a decrease in persistence and dimensionality, and higher ISP afterward. Additionally, SSWs (SPVs) exhibit a suppression (enhancement) of Rossby wave activity in the stratosphere and to a lesser extent in the troposphere for eastwards traveling waves.