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Solar Wind Turbulence Solar Wind Turbulence A Study of Corotating Interaction Regions at AU Jerey A Tessein DepartmentofPhysics University of New Hampshire Durham NH May Abstract The solar wind is a sup ersonic ow of plasma coming out of the Sun and propagating throughout the heliosphere Because of the Suns rotation and the variability in the source of the solar wind fast moving wind can crash into slow wind This results in an interface that can rep eat as the Sun rotates known as a Corotating Interaction Region CIR where the slippage of fast wind past slow wind is a source of turbulence Ihave taken CIR events from the solar minimum years and to analyze their turbulence parameters and compared them to nonCIR ambient turbulence from solar maximum years The CIR turbulence diers from the ambient turbulence b ecause it is eectively a p ointsourceand the hop e is to nd evidence of turbulent energy emanating from the interface This should present some nonhomogeneities not seen by nonCIR turbulence We nd that there are some dierences with the CIR turbulence but for the most part the CIR turbulence has the same results as past turbulence studies This most likely means that the evolution of solar wind turbulence is faster than that of the source Contents Basics of the Solar Wind Prop erties of the Solar Wind Magnetosphere Termination Sho ck History of Solar Wind Measurements Current Missions Solar Cycle Coronal Mass Ejections Origin of the Solar Wind Parker Solutions Three Mathematical Approaches to the Solar Wind Solar Wind Development Bulk Solar Wind at AU Fast And Slow Wind Transients in the Solar Wind Sho cks Corotating Interaction Regions Magnetic Clouds Cosmic Rays Plasma Magnetohydro dynamics Plasma Waves Fluctuations Developmentofturbulence Sp ectral Index Geometry Inertial Range Dissipation Range Helios Observations Dierences Between Fast and SlowWind Smaller Scale Analyses Tessein Hourly Analysis Background DataAnalysis ACE s Merged Data i ACE High Reolution MAG Data Analysis Helios MAG Data Conclusions Corotating Interaction Regions at AU Motivation Data Results Discussion ii Acknowledgements First and foremost I would liketothankmy advisor Dr Charles W Smith without whom none of this would b e p ossible I have come a long way from the rst year physics ma jor I was several years ago Working for Dr Smith has op ened many do ors for me including publications attending meetings and acceptance to graduate scho ol The career path that lays ahead of me has b een made p ossible by his excellentmentoring Iwould like to thank my fellowphysics ma jors who have b een excellent supp ort over the last four years Instead of b eing in constant comp etition with one another my class has b een more like a supp ortivecommunityofwhich b eing a memb er has b een a pleasant exp erience Iwould also like to thank Dr Bernie Vasquez for helping out with some imp ortant things Lastly I need to thank my family and friends They are go o d p eople and have always b een there for me Chapter Basics of the Solar Wind Prop erties of the Solar Wind The solar wind is a sup ersonic gas propagating throughout interplanetary space It is an extension of the solar atmosphere driven by the dierence in gas pressure b etween the Sun and space The vast ma jority of the constituent particles are protons and alpha particles He Helium also has an average abundance of bynumb er In addition isotop es up to Iron have b een observed The solar wind has an average densityofabout cm near Earth Density is dep endent on solar activity and wind sp eed during times of solar activity the density tends to spike Wind sp eed can vary from kms to kms however nominal sp eed during times of reduced solar activity is kms to kms The average temp erature is ab out K although at such an extremelylowdensity there is very little heat capacity Like density the temp erature is related to solar activity Just as with Earth the Sun has a mostly dip olar magnetic eld The pro cess that generates the magnetic eld is called a dynamo It is susp ected that the magnetic eld is generated by rotating charged uid in the interior The solar magnetic eld encompasses the entire solar system and is known as the Interplanetary Magnetic Field hereafter referred to as the IMF The IMF is coupled to the solar wind and is carried out by it Lo cal electromagnetic interactions are governed by the geometry of the IMF Ions gyrate around the eld lines The gyration has a characteristic radius given by mv r jB j Magnetosphere When the solar wind reaches a planet with a magnetic eld like Earth it interacts Earths magnetic eld generates a barrier around the planet known as the magnetosphere On the day side of the magnetosphere and around part of the night side there exists an interface known as the b ow sho ck This is the lo cation where the ram pressure of the solar wind equilibrates with the magnetic pressure of Earths magnetosphere This eect is similar to arockinafastmoving river There is a stationary sho ckwave in the stream that causes the water to slide around the ro ck In the case of the magnetopause the sho ckdoesmove dep ending on the pressure from solar wind for example a solar storm can compress the bow sho ck closer to Earth Likewise during quiet solar wind Earths magnetic eld is Figure Artists rendition of the heliosphere Image courtesy of NASA able to push the b ow sho cksunward As the solar wind is diverted around the side of the magnetosphere it forms a long narrowing b oundary on the night side of Earth called the magnetotail Termination Sho ck The solar wind extends out to approximately AUAU is equivalent to the EarthSun distance where it reaches the termination sho ck This is the p oint where pressure from the solar wind balances with the Lo cal Interstellar Medium LISM When the the solar wind reaches the heliopause it joins with the ow of the LISM The termination sho ck completely surrounds the heliosphere and is approximately bullet shap ed The sho ck has b ecome an ob ject of study in recentyears b ecause we are getting our rst in situ measurements of it from Voyagers and An artists depiction of the entire heliosphere is shown in Figure History of Solar Wind Measurements Studies of solarterrestrial relations have a long history Before the space age there were numerous ways to remotely measure the eects of solar activity on our planet Aurora studies go back thousands of years and chemical analysis of tree rings is also an indicator of the sunsp ot record sunsp ot numb er correlates to solar activity A lack of solar activity from to called the Maunder Minimum has b een linked to unusually cold weather Viking settlements in Greenland correpsond to what is known as the Medievel Warm Perio d immediately preceeding the Maunder Minimum During the Maunder Minimum Vikings abandoned Greenland p ossibly due to climate change In the twentieth century studies of comet tails p ortended the existence of a solar wind Astronomers found that comets contain a second tail that always p oints antisunwardInadditiontoadusty tail a comet has a second tail that contains ions This is known as a plasma tail The observation that the plasma tail always p oints antisunward meant that there must b e a continuous solar wind During the early s most astronomers thought that the solar wind only came in intermittent bubbles It was referred to as solar corpuscular radiation In Eugene Parker predicted the existence of a continuous sup ersonic solar wind This was so on conrmed by in situ measurements from early satellites This forms the basis for our current picture of the solar wind Current Missions The arrival of the space age has greatly increased our knowledge of the solar wind In the s the Helios spacecraft wentwithinAU of the Sun the closest of any spacecraft to date A new mission Solar Prob e is scheduled to get much closer to the Sun around The twoVoyager spacecraft launched in have reached the termination sho ck and are returning the rst in situ measurements of the b oundary regions b etween the Heliosphere and the LISM As of the IBEX mission is mapping the termination sho ckby measuring neutral particles coming in from the LISM Ulysses launched in did several p olar orbits ab out the Sun revealing much ab out prop erties of the highlatitude solar wind The spacecraft that will b e used for this thesis ACE Advanced Comp osition Explorer was launched in and takes plasma measurements at the L p ointbetween the Sun and Earth Solar Cycle ween stages of solar min The Sun go es through eleven year cycles of activity switching b et imum and solar maximum This eect is thought to b e a result of the Suns dierential rotation Because the Sun is not a rigid b o dy its equatorial regions rotate faster than the p olar regions Because low latitudes
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