the solar wind is a highly ionized , magnetized plasma which flows at supersonic and superalfvnic speeds away from the sun . in this medium there have been many observations of enhanced magnetic fluctuations at frequencies near the proton cyclotron frequency . there are two hypotheses as to the source of these enhanced fluctuation events [ jian et al . , one school holds that these largeamplitude waves are generated close to the sun and are then transported by the solar wind to observation at planetary distances . the alternative picture is that the expanding solar wind flow leads to nonthermal electron and ion velocity distributions which locally excite shortwavelength instabilities which are observed near their source . this manuscript uses plasma and magnetic field measurements with kinetic linear dispersion theory to demonstrate that several enhanced magnetic fluctuations events observed by the wind spacecraft on 19 march 2005 are unstable to one or more kinetic instabilities , thereby providing evidence that these particular events are locally generated . the hot ( tens of ev ) , tenuous ( few particles per cubic centimeter near 1  au ) character of the solar wind implies that it is a collisionless plasma in which a variety of different kinetic instabilities can arise if appropriate sources of free energy are available . kinetic instabilities are those which are driven by velocityspace anisotropies and which typically have maximum growth rates arising in the short wavelength regime corresponding to wavelengths the order of or shorter than either the thermal ion gyroradius or the ion inertial length [ gary , 1993 ] . if a plasma is in equilibrium , the velocity distributions of the constituent species are maxwellian . all fluctuations in such plasmas either are damped or propagate with no change in amplitude . for frequencies near the proton cyclotron frequency and propagation quasiparallel to b o , the cases of interest here , there are three fundamental normal modes [ gary , 1993 , chapter 6 ] : predominantly electrostatic ion acoustic waves , predominantly electromagnetic alfvncyclotron waves with lefthand circular polarization in the limit of k x b 
 o  =  0 , and predominantly electromagnetic magnetosonic waves with righthand circular polarization at k x b 
 o  =  0 . ion acoustic waves propagate with weak damping only if te  >  >  tp ; as this is not a typical condition in the solar wind , we do not consider such modes further . at very long wavelengths and low frequencies alfvn waves at k x bo  =  0 are nonresonant and essentially undamped . but as the frequencies of such modes approach p , the proton cyclotron frequency , the waves become dispersive ; the resulting alfvncyclotron fluctuations undergo proton cyclotron damping and propagate with real frequencies only at r <  p . longwavelength magnetosonic fluctuations k x bo  =  0 are also nonresonant and very weakly damped , but because of their righthand polarization , they do not suffer proton cyclotron damping and propagate at frequencies through and well above p where they become strongly dispersive whistler modes . although various types of nonthermal ion and electron velocity distributions are observed in the interplanetary medium [ feldman et al . , 1973 ; marsch , 1991 ] , especially in the fast wind , for purposes of instability analysis nonequilibrium distributions are usually characterized as having temperature anisotropies and/or multiple components with relative flow speeds between component pairs . here , 1973 ; leubner and vias , 1986 ; marsch and livi , 1987 ; goldstein et al . , 2000 ; he et al . , 2015 ] and assume that proton velocity distributions can be fit as the sum of two components , a more dense , slower core ( denoted by subscript c ) and a less dense , faster beam ( subscript b ) . we further assume that both proton components , as well as the electrons ( subscript e ) and the alpha particles ( subscript  ) , can each be represented as a bimaxwellian distribution with t    t|| ( where the subscripts represent directions relative to b 
 o ) and relative flow velocities parallel to b 
 o. we denote the relative beam / core flow velocity as v 
 o  =  v 
 ob  v 
 oc where v 
 oj is the average flow velocity of the jth component in the plasma ( center of mass ) frame and the relative alpha / core flow velocity as v 
 oc 
 =  v 
 ov 
 oc . we define the ion ( electron ) inertial length i  =  c/pi ( e  =  c/pe ) where  
 pj is the plasma frequency of the jth species , and the ion ( electron ) thermal gyroradius i  =  vi/i ( e  =  ve/e ) where vj is the thermal speed of the jth species , and j is the cyclotron frequency of the jth species . the jth component parallel plasma beta is defined as ||j  =  8njkbt||j / bo 
 , and the alfvn speed is va  =  bo/(4nemp ) where ne  =  np  +  2n. anisotropies in solar wind ion velocity distributions are a rich source of diverse kinetic plasma instabilities . the enhanced fluctuations that arise from such growing modes scatter the nonthermal species , reducing their anisotropies and driving them toward ( but not completely to ) the maxwellian distributions of thermal equilibrium [ e.g. , gary et al . [ 2009 , 2010 , 2014 ] ( see also s. a. boardsen et al . , mercury surface , space environment , geochemistry , and ranging ( messenger ) survey of in situ lowfrequency wave storms between 0.3 and 0.7  au , submitted to journal of geophysical research , 2015 ) have used highresolution magnetometer observations from the stereo , messenger , and helios spacecraft to study solar wind events of enhanced magnetic field fluctuations with frequencies near p at propagation quasiparallel to the background magnetic field b 
 o. by comparing lefthand versus righthand polarizations in the spacecraft frame , they found that the lefthand waves are generally stronger and appear slightly more often . however , their analyses utilized proton data reduction algorithms which were less general than the beam / core bimaxwellian velocity distributions used in this paper , thereby limiting their ability to compare temperature anisotropy and beam / core distributions as sources of protondriven instabilities . here we follow these earlier papers by identifying events of interest as corresponding to enhanced field fluctuations with frequencies near the proton cyclotron frequency . the new element here is that we correlate these events with particle species observations under the more general and more accurate assumption that the proton distributions can be described as the sum of beam and core components with separate densities , flow speeds , temperatures , and temperature anisotropies . using this model in kinetic linear dispersion theory , we determine which types of iondriven instabilities are the likely sources of these enhanced fluctuation events . [ 2009 , 2010 , 2014 ] , our concerns here are iondriven instabilities which propagate at directions quasiparallel to b 
 o. this condition corresponds to three categories of growing modes : alfvncyclotron instabilities driven by ion component anisotropies such that t / t||  >  1 [ gary et al . , 2001 ] , parallel firehose instabilities driven by ion component anisotropies such that t / t||  <  1 [ hellinger et al . , 2006 ] , and ion / ion magnetosonic instabilities driven by the relative flow speed of two ion components [ goldstein et al . , 2000 ] . under the condition k x b 
 o  =  0 alfvncyclotron waves and instabilities have lefthand circular polarization , whereas the parallel firehose instability , magnetosonic waves , and magnetosonic proton / proton instabilities all have righthand circular polarization in the solar wind frame . if the proton velocity distribution may be approximated as a single bimaxwellian and heavy ions may be ignored , growth rate predictions of kinetic linear theory of electromagnetic instabilities driven by proton temperature anisotropies may be expressed in terms of two parameters , tp / t||p and ||p . figure  7.3 of gary   shows that these two parameters characterize the linear theory thresholds of such instabilities . gary et al .   used hybrid simulations to show that the alfvncyclotron instability threshold condition represents an upper bound for tp / t||p  >  1 , and gary et al .   used the same type of simulations to show that the protonparallel firehose instability threshold constitutes an upper bound for the opposite sense of the proton anisotropy . considering only solar wind conditions in which the proton velocity distribution may be approximated as a single bimaxwellian component , kasper et al . [ 2002 , 2006 ] , hellinger et al . , bale et al . , maruca et al . [ 2011 , 2012 ] , osman et al . , and hellinger and trvnek   used measurements from the wind spacecraft to show that instability thresholds in tp / t||p versus ||p parameter space indeed correspond to observed proton anisotropy bounds . however , thresholds of the proton mirror and the oblique proton firehose instabilities , which have wavevectors at substantially oblique angles relative to b 
 o , provide better constraints to the observations than do the thresholds of the anisotropydriven instabilities with maximum growth at parallel propagation . furthermore , as discussed above , proton velocity distributions in the relatively fast , relatively collisionless solar wind are usually not well represented as a single bimaxwellian , but rather require at the minimum a two component core / beam description . linear dispersion theory analyses have demonstrated that a sufficiently large beam / core relative flow speed ( typically greater than about 1.5  va ) can drive both parallel magnetosonic and oblique alfvn instabilities [ montgomery et al . , 1975 , 1976 ; abrahamshrauner et al . , 1979 ; dum et al . , 1980 ; marsch and livi , 1987 ; daughton and gary , 1998 ; goldstein et al . , 2000 ] . however , kinetic linear theories of proton beam / core instabilities require at least six independent proton parameters , e.g. , the proton core || , the proton core relative density nc / ne , the dimensionless beam / core relative flow speed vo / va , t||b / t||c , and the two proton component temperature anisotropies tc / t||c and tb / t||b , as well as one or more electron parameters [ daughton and gary , 1998 ] and at least four additional parameters characterizing each minor ion species such as the alpha particles . this parametric plethora makes it difficult to present linear theory threshold conditions of beam / core instabilities as twodimensional plots , requiring instead a large number of multidimensional figures to clearly expose the plasma physics of these growing modes . our approach here is to constrain this large parameter space through the use of detailed ion and electron measurements from the plasma instruments on board the wind spacecraft and to calculate dispersion properties of the enhanced fluctuations for specific conditions observed in the solar wind . the first is that undetermined processes in the collisionless solar wind ( e.g. , shocks , diverging flows , and/or largescale compressions ) act locally to push plasma species velocity distributions away from the maxwellian condition . the second is that the resulting nonmaxwellian distributions drive shortwavelength instabilities which generate enhanced field fluctuations which , in turn , act to stabilize the growing modes by reducing the distribution anisotropies . in this scenario the largeamplitude wave events we study should correspond to marginally stable or weakly unstable modes . our conclusion that the plasma observations are indeed subject to modest instability growth the wind spacecraft carries a fast magnetometer [ lepping et al . , 1995 ] , a pair of faraday cup instruments as part of the solar wind experiment ( swe ) [ ogilvie et al . , 1995 ] which measures velocity distributions of protons and alpha particles at a 92  s cadence and an electron electrostatic analyzer [ lin et al . , 1995 ] providing a full 3d electron velocity distribution at a 97  s cadence . after completing a survey of enhanced magnetic fluctuation events in the observed frequency range 0.01  hz  <  f  <  5  hz using 0.092  s magnetic field data , we chose observations of such events in the solar wind on 19 march 2005 to be the subject of a comprehensive study as described below . on this date the wind spacecraft detected a number of events with wave propagation quasiparallel to the background magnetic field . we chose the events on this date because both lefthand and righthand polarized waves in the spacecraft frame are observed within a relatively short time interval , and the individual ion spectra from this period have been examined in detail by the swe coauthors on this manuscript . figure  1 illustrates the dynamic spectrum of the magnetic field data from 19 march 2005 . this analysis utilizes a fast fourier transform based on the means   quadrature spectrum technique , which is explained in jian et al . . as shown in figure  1 , we found seven events of enhanced magnetic fluctuations , with the following common characteristics : ( 1 ) the coherence between the two transverse magnetic field components by and bz is enhanced , ( 2 ) the transverse power is substantially increased over the background power at earlier and later times , ( 3 ) the transverse power is much stronger than the compressional power , ( 4 ) the magnetic field fluctuations are nearly circularly polarized as indicated by the high absolute ellipticity , and ( 5 ) the propagation direction is within 10 of the background magnetic field direction . given these seven candidate events , we performed linear dispersion theory analyses for most of these intervals , using the method described below . the events meeting the criteria in jian et al . are marked in figure  2 , cyan for lefthand polarized in the spacecraft frame and yellow for righthand polarized in the spacecraft frame . the intervals for the seven events indicated in figure  1 are as follows : event # 1 ( 78.380  <  doy  <  78.389 ) , event # 2 ( 78.488  <  doy  <  78.494 ) , event # 3 ( 78.506  <  doy < 78.515 ) , event # 4 ( 78.672  <  doy  <  78.685 ) , event # 5 ( 78.741  <  doy <  78.748 ) , event # 6 ( 78.786  <  doy  <  78.798 ) , and event # 7 ( 78.804  <  doy <  78.811 ) . magnetic field fluctuation measurements from the wind spacecraft on 19 march 2005 . ( a ) coherence between the two transverse components , by and bz ; ( b ) transverse power spectral density ; ( c ) the ellipticity in the spacecraft frame where + 1 corresponds to righthand circular polarization , and 1 corresponds to lefthand circular polarization ; and ( d ) the propagation angle with respect to b 
 o. the yellow lines represent the local proton cyclotron frequency . the white solid and dashed lines labeled fsc+ and fsc represent the dopplershifted proton cyclotron frequency if the wave propagates parallel or antiparallel to the solar wind velocity under the assumption that the phase speed of a wave at the proton cyclotron frequency is v 
 a. the fast fourier transform is performed for every 2560 points with a shift of 320 points and a bandwidth of 29 points . in figures  1b through 1d the color black represents parameter values for which the by and bz coherence is less than 0.5 . magnetic field and plasma measurements from the wind spacecraft as a function of time for 19 march 2005 . ( a ) the magnetic field vector in gse coordinates , where black represents the field magnitude , and red , green and blue represent bx , by , and bz , respectively . for the plasma properties shown in the subsequent five panels proton core parameters are indicated by red dots , proton beam parameters as blue dots , alpha particle parameters as magenta dots , and electron parameters as green dots . here are shown ( b ) the component number densities , ( c ) the average velocities in the x gse direction , ( d ) the average flow speed parallel to b 
 o relative to the core protons and normalized to the alfvn speed , ( e ) the component || , and ( f ) the component t/t|| values . the seven events corresponding to enhanced proton cyclotron fluctuations discussed in the text are shown as vertical bands with cyan corresponding to lefthand polarization and yellow representing righthand polarization as measured in the spacecraft frame . for one 92  s measurement cycle of the ions in each event , the proton core , the proton beam , the electrons , and the alpha particles were each fit to bimaxwellian velocity distributions with relative flow velocities parallel to b 
 o. the proton beam and alpha particle measurements during event # 5 are noisy and poorly defined , so this event is not further considered here . table  1 presents field and plasma parameters from the other six events analyzed in section 3 . due to weak signaltonoise ratios and/or strongly nonmaxwellian distributions , the fitting procedures from events # 2 through # 7 yield relatively large error bars for many of the alpha parameters . the values of the alpha temperature anisotropies are particularly suspect , so that because of these large uncertainties , we have assumed t/t||  =  1 for events # 2 , # 3 , # 4 , # 6 , and # 7 in table  1 and in the linear dispersion theory analyses described in section 3 . field and plasma parameters for six enhanced magnetic fluctuation events observed from wind spacecraft on 19 march 2005a 
  values in parenthesis represent the assumption of isotropic alpha particles because of poor fits to the model of flowing bimaxwellian alpha particle velocity distributions . figure  2 displays the magnetic field vector in geocentric solar equatorial ( gse ) coordinates , the number density , speed in the x direction ( antisunward ) , the dimensionless beam / core and alpha / core relative flow speeds , ||j , and temperature anisotropy of core proton ( in red ) , beam proton ( in blue ) , alpha particles ( in magenta ) , and electrons ( in green ) . for all seven events , bx  >  0 , implying that this component of the magnetic field points sunward . also for all seven events vocx >  0 , vobx  <  0 , and vox  <  0 so that the beam / core relative flow points in the antisunward direction . figure  3 illustrates the magnetic fluctuation power spectra for four of these events as labeled . as is typical for solar wind events , 2014 , figure  7b ] , the energy density of field fluctuations transverse to b 
 o is 1 to 2 orders of magnitude greater than that of the compressional fluctuations parallel / antiparallel to the background magnetic field . polarization analysis shows that the fluctuations of events # 1 , # 6 , and # 7 are predominantly lefthand polarized , whereas event # 4 corresponds primarily to righthand polarization fluctuations as measured in the spacecraft frame . the magnetic fluctuation power spectra during events # 1 , # 4 , # 6 , and # 7 observed from the wind spacecraft on 19 march 2005 . figure  4 shows selected ion measurements from the swe instrument during event # 1 . here bn indicates the angle between the magnetic field vector and the projection axis on which the distribution was measured ( a selection of 5 out of the 40 spin angles that make up the fit ) . the proton beam / core separation is clear here , as is the alpha / core relative flow . ( first column ) the stepwise black lines show the relative flux measurements from the swe instrument as functions of energy / charge for five different values of bn , the angle between b 
 o and the projection axis on which the distribution was measured . the smooth curves display the ion distribution fits for proton core ( red ) , proton beam , ( blue ) , and alpha particle ( violet ) components . ( second column ) the proton and alpha particle velocity distributions in v||v space as represented by the proton core , proton beam , and alpha particle fits . this section describes results from kinetic linear dispersion theory of waves and instabilities in collisionless , homogeneous , magnetized plasmas [ gary , 1993 ] , using parameters as measured from wind during the events of 19 march 2005 . under the assumption that the enhanced fluctuations from each of these events were generated in the local solar wind , we have used magnetic field and plasma measurements as listed in table  1 . inserting these parameters into the kinetic linear dispersion theory for waves and instabilities at k x b 
 o  =  0 , we computed and plotted the dispersion properties , that is , the complex frequency   =  r  +  i as a function of parallel wave number k|| , of the four distinct lowfrequency waves at k x b 
 o  =  0 for each event . all of the linear theory calculations presented here are carried out in the plasma centerofmass frame where bo  >  0 corresponds to the sunward direction . the parameters for event # 1 given in table  1 yield figure  5 which illustrates the dispersion relations ( r and  versus k|| ) for each of the modes which propagate near the proton cyclotron frequency . the two lefthand polarized alfvncyclotron modes are constrained to |r|  <  p with one such mode stable and one unstable . if the proton velocity distribution were to consist of a single bimaxwellian component , the sunward and antisunward alfvncyclotron modes would be unstable with the same growth rates . however , the beam / core character of the observed proton distributions breaks the leftright symmetry of the system for all the events studied here . in this particular case the positive frequency sunward propagating alfvncyclotron mode is stable , whereas the negative frequency antisunward propagating alfvncyclotron mode is moderately unstable ( maximum /p  ~  5    10 ) at k||c/pp  ~  0.60 , where it has a strong proton core cyclotron resonance and is driven by the strong core temperature anisotropy . the two righthand polarized magnetosonic modes , in contrast , extend to frequencies well above p where , in the absence of proton cyclotron resonances , they remain weakly damped and exhibit the beginnings of whistler dispersion . the dispersion properties ( ( a ) real frequencies and ( b ) damping / growth rates as functions of k|| ) of the four lowfrequency electromagnetic normal modes of the plasma computed from the kinetic dispersion equation at k x b 
 o  =  0 for fluctuations in a homogeneous , collisionless plasma . parameters are those as given in table  1 for event # 1 on 19 march 2005 . red and orange represent properties of the righthand circularly polarized magnetosonic modes , whereas black and blue illustrate dispersion of the lefthand circularly polarized alfvncyclotron modes . the parameters for event # 2 yield figure  6 which illustrates the dispersion relations for each of the modes that propagate near the proton cyclotron frequency . the two lefthand polarized alfvncyclotron modes are constrained to |r|  <  p and become strongly damped at k||c/pp  >  0.40 . the righthand polarized magnetosonic modes again extend to higher frequencies with weak damping and whistler dispersion . here the negative frequency magnetosonic branch is moderately unstable ( maximum /p  ~  2    10 ) at k||c/pp  ~  0.80 and r/p  ~  1.0 , with a strong proton beam cyclotron resonance and is driven by the superalfvnic beam / core relative flow ( this growing mode is also known as the proton / proton righthand resonant instability [ gary , 1993 , section 8.2 ] ) . the negative phase speed again indicates that unstable modes here propagate in the antisunward direction . the dispersion properties ( ( a ) real frequencies and ( b ) damping / growth rates as functions of k|| ) of the four low frequency electromagnetic normal modes of the plasma computed from the kinetic dispersion equation at k x b 
 o  =  0 for fluctuations in a homogeneous , collisionless plasma . parameters are those as given in table  1 for event # 2 on 19 march 2005 . red and orange represent properties of the righthand circularly polarized magnetosonic modes , whereas black and blue illustrate dispersion of the lefthand circularly polarized alfvncyclotron modes . the parameters for event # 3 yield r(k|| ) dispersion plots very similar to those for the two preceding events . beam / core and alpha / core relative flow speeds are not large enough to excite the ion / ion magnetosonic instabilities , so that all four modes are stable for this event and we do not illustrate this case . the parameters for event # 4 as given in table  1 yield dispersion plots r(k|| ) with two distinct unstable modes as shown in figure  7 . again the righthand polarized magnetosonic mode is unstable with maximum growth rate /p  ~  7    10 and corresponding wave number k||c/pp  ~  0.35 and frequency r/p  ~  0.33 , whereas the lefthand polarized alfvncyclotron mode is more weakly unstable with maximum growth rate /p  ~  2    10 and corresponding wavenumber k||c/pp  ~  0.24 and frequency r/p  ~  0.12 . it appears that both the beam / core and the alpha / core relative flows contribute to the magnetosonic instability and that the alfvncyclotron instability is driven primarily by the beam temperature anisotropy . the other two modes are stable , being undamped at long wavelengths and becoming strongly damped at sufficiently large wave numbers . the dispersion properties ( ( a ) real frequencies and ( b ) damping / growth rates as functions of k|| ) of the four low frequency electromagnetic normal modes of the plasma computed from the kinetic dispersion equation at k x b 
 o  =  0 for fluctuations in a homogeneous , collisionless plasma . parameters are those as given in table  1 for event # 4 on 19 march 2005 . red and orange represent properties of the righthand circularly polarized magnetosonic modes , whereas black and blue illustrate dispersion of the lefthand circularly polarized alfvncyclotron modes . for the parameters of event # 6 , the righthand polarized magnetosonic mode is again unstable , apparently driven by the beam / core relative flow . dispersion of both r(k|| ) and (k|| ) is similar to previous cases and is not shown here ; the maximum growth rate is very weak with /p  <  1    10 and corresponds to k||c/pp  ~  0.63 and r/p  ~  0.72 . again , the unstable modes propagate in the antisunward direction . finally , for the parameters of event # 7 , both the alfvncyclotron and the magnetosonic modes are unstable . dispersion of both r(k|| ) and (k|| ) is similar to previous cases and is not shown here . the maximum growth rate of the alfvncyclotron instability is weak with /p  ~  1.3    10 and corresponds to k||c/pp  ~  0.40 and r/p  ~  0.20 , and the magnetosonic mode has very weak growth with /p  <  2    10 at k||c/pp  ~  0.25 and r/p  ~  0.23 . we have used wind spacecraft magnetic field and plasma observations in the slow solar wind ( vsw  ~  390  km / s ) on 19 march 2005 to examine the linear dispersion properties for events of enhanced magnetic fluctuations near the proton cyclotron frequency at propagation parallel / antiparallel to the background magnetic field . we analyze the velocity distributions in terms of two proton components , a more dense , cooler core and a more tenuous , warmer beam with a relative beam / core flow parallel to b 
 o , and a very tenuous , flowing alpha particle component . we then solve the kinetic linear dispersion equation at k x bo  =  0 and find for two events the most unstable mode is the lefthand polarized alfvncyclotron instability driven by a proton component temperature anisotropy t/t||  >  1 , and for three events the most unstable mode is the righthand polarized magnetosonic instability driven primarily by ion component relative flows . jian et al .   argued that , for waves propagating parallel to the solar wind flow velocity v 
 sw , the spacecraft frame polarization should be the same as the polarization in the solar wind frame , whereas for waves at propagation antiparallel to v 
 sw , the spacecraft frame polarization should be opposite to the intrinsic polarization . our dispersion analysis predicts that , for all five events with unstable modes , the instabilities propagated parallel to the direction of the proton beam , i.e. , in the antisunward direction . thus , as summarized in table  2 , we get agreement between polarizations inferred from observations and polarizations predicted by linear theory for four out of the five events . the single case of disagreement between observations and theory ( event # 6 ) may be due to the fact that in this case theory predicts very weak growth for the righthand plasma frame instabilities , so that this disagreement is not as robust as the four cases of agreement . polarization table for the six events of 19 march 2005 analyzed herea 
  observed polarizations are as given in figure  2 , inferred polarizations follow from table  a1 assuming antisolar propagation , and theoretical polarizations are obtained from the most unstable modes as predicted by the linear dispersion theory analyses described in section 3 . the observations of enhanced electromagnetic fluctuations near the proton cyclotron frequency in the solar wind have been credited to two distinct sources . the nonlocal hypothesis holds that these waves are generated near the sun and are then transported by the solar wind flow to observation at planetary distances . an alternate scenario is that the expanding solar wind flow leads to nonthermal particle velocity distributions which excite kinetic instabilities throughout the heliosphere so that the enhanced waves are generated locally , near the source of their observation . our work demonstrates a clear correlation between such enhanced fluctuations and proton velocity distributions sufficiently anisotropic to locally drive kinetic instabilities . this work does not disprove the nonlocal hypothesis but does demonstrate that local sources of fluctuations should be taken into account in studies of solar wind turbulence and its evolution with distance from the sun , as suggested by bale et al . . other topics worthy of future study are the sources of the ion anisotropies which drive the kinetic instabilities . what creates the solar wind t/t||  >  1 condition which , in turn , drives the alfvncyclotron instability ? what is the source of the beam / core proton distribution [ see , for example , maneva et al . , these results should not be construed as fully representative of enhanced fluctuation activity near the proton cyclotron frequency in the solar wind . as discussed in jian et al . , such events could also include both intrinsically righthand polarized waves driven by the alpha / proton magnetosonic instability [ gomberoff et al . 2000a , 2000b ; li and habbal , 2000 ; araneda et al . , 2002 ; lu et al . , 2006 ; verscharen et al . , 2013 ; verscharen and chandran , 2013 ] , and the intrinsically lefthand polarized waves driven by the t/t||  >  1 anisotropy on heavy ion velocity distributions . understanding which events correspond to which free energies and to which normal modes will require substantial additional studies of proton cyclotron events under a wide variety of solar wind conditions including fast as well as slow wind , both high and low proton  , and a broad range of beam / core relative flow speeds . however , we believe that the present work clearly demonstrates that the sometimesinvoked assumption that all such events are due to the alfvncyclotron instability is invalid .
abstractintervals of enhanced magnetic fluctuations have been frequently observed in the solar wind . 
 but it remains an open question as to whether these waves are generated at the sun and then transported outward by the solar wind or generated locally in the interplanetary medium . 
 magnetic field and plasma measurements from the wind spacecraft under slow solar wind conditions on 19 march 2005 demonstrate seven events of enhanced magnetic fluctuations at spacecraftframe frequencies somewhat above the proton cyclotron frequency and propagation approximately parallel or antiparallel to the background magnetic field b 
 o. the proton velocity distributions during these events are characterized by two components : a more dense , slower core and a less dense , faster beam . observed plasma parameters are used in a kinetic linear dispersion equation analysis for electromagnetic fluctuations at k x b 
 o  =  0 ; for two events the most unstable mode is the alfvncyclotron instability driven by a proton component temperature anisotropy t/t||  >  1 ( where the subscripts denote directions relative to b 
 o ) , and for three events the most unstable mode is the righthand polarized magnetosonic instability driven primarily by ion component relative flows . 
 thus , both types of ion anisotropies and both types of instabilities are likely to be local sources of these enhanced fluctuation events in the solar wind .