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Nayar, S. R. Prabhakaran; Nair, Vipin A.; Radhika, V. N.; Revathy, K.

doi:10.1023/a:1017599621110

Cited by 31 publications

(5 citation statements)

References 16 publications

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“…[40] Several studies note these rotation periods in solar wind data and in A p over many solar cycles [Hauska et al, 1973;Prabhakaran Nayar et al, 2001;Temmer et al, 2007]. In particular, Prabhakaran Nayar et al [2001] looks at variations of solar wind and A p at periodicities of 9 and 27 days and finds that both track the solar cycle; that is the peak power for both occur near solar maximum.…”

Section: Results From Individual Years 321 Year 2002mentioning

confidence: 99%

A multiyear (2002–2006) climatology of O/N₂ in the lower thermosphere from TIMED GUVI and ground‐based photometer observations

et al. 2012

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[1] The Mass Spectrometer and Incoherent Scatter (MSIS) series of models has been a standard for specification and prediction of conditions in the Earth's thermosphere. One aspect of the model that has not been well validated is its predictions of the lower thermospheric compositional response to varying periodic and transient solar and geomagnetic forcings. Here we compare the predictions by the NRLMSIS model over the years 2002 to 2006 for column O/N 2 with GUVI satellite (daytime) observations at a fixed longitude of the Poker Flat Research Range in central Alaska. NRLMSIS predictions are also compared with nightside auroral O/N 2 observations obtained from ground-based photometric measurements from central Alaska. While there is often good agreement between the GUVI and NRLMSIS O/N 2 at high latitudes, there are also times during large geomagnetic storms when there is some disagreement with the largest occurring at midlatitudes. The 9-day periodicity, first described in 2007 and attributed to high-speed solar wind streams, is present in the model at all latitudes but is quite weak in the observations below 55N latitude. Away from high-latitudes, these differences may exist because the NRLMSIS O/N 2 dependence on a p forces nonperiodic contributions contained in the NRLMSIS database to give a periodic response when a p is varied periodically. While the nighttime observations show considerable agreement with NRLMSIS they are much more variable than predicted by the model. This variability suggests that there are significant local effects in the auroral zone that are not captured by the model.

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Section: Results From Individual Years 321 Year 2002mentioning

confidence: 99%

A multiyear (2002–2006) climatology of O/N₂ in the lower thermosphere from TIMED GUVI and ground‐based photometer observations

et al. 2012

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“…Common solar timescales ranging from a decade down to hours have been characterized, and timescales of the order of a Carrington Rotation period (approx. 27 days) and shorter (e.g., 14, 9, and 7 days) have been consistently identified in various heliospheric and geomagnetic data (e.g., Bolzan et al 2005;Fenimore et al 1978;Gonzalez & Gonzalez 1987;Gonzalez et al 1993;Mursula & Zieger 1998;Prabhakaran Nayar et al 2001Svalgaard & Wilcox 1975). Temmer et al (2007) linked the 9 day timescale to coronal hole variability in the declining phase of solar cycle 23 and Neugebauer et al (1997) used wavelet analyses of Ulysses solar wind speed data to investigate polar microstreams occurring on timescales of 16 hours.…”

Section: Introductionmentioning

confidence: 81%

Analysis of High Cadence in Situ Solar Wind Ionic Composition Data Using Wavelet Power Spectra Confidence Levels

Edmondson

Lynch

Lepri

et al. 2013

ApJS

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The variability inherent in solar wind composition has implications for the variability of the physical conditions in its coronal source regions, providing constraints on models of coronal heating and solar wind generation. We present a generalized prescription for constructing a wavelet power significance measure (confidence level) for the purpose of characterizing the effects of missing data in high cadence solar wind ionic composition measurements. We describe the data gaps present in the 12-minute ACE/SWICS observations of O 7+ /O 6+ during 2008. The decomposition of the in-situ observations into a 'good measurement' and a 'no measurement' signal allows us to evaluate the performance of a filler signal, i.e., various prescriptions for filling the data gaps. We construct Monte Carlo simulations of synthetic O 7+ /O 6+ composition data and impose the actual data gaps that exist in the observations in order to investigate two different filler signals: one, a linear interpolation between neighboring good data points, and two, the constant mean value of the measured data. Applied to these synthetic data plus filler signal combinations, we quantify the ability of the power spectra significance level procedure to reproduce the ensemble-averaged time-integrated wavelet power per scale of an ideal case, i.e. the synthetic data without imposed data gaps. Finally, we present the wavelet power spectra for the O 7+ /O 6+ data using the confidence levels derived from both the Mean Value and Linear Interpolation data gap filling signals and discuss the results.

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“…Ephemeral periodicities associated with solar flares (27, 59, 137, and 330 days) and coronal mass ejections (37, 97, 182, and 365 days) have been reported by Polygiannakis et al (2002). Timescales of order the Carrington Rotation, 27 days and its harmonics (e.g., 13.5, 9, and 6.7 days) have been consistently identified from solar wind speed, IMF, and geomagnetic data (e.g., Bolzan et al 2005;Fenimore et al 1978;Gonzalez & Gonzalez 1987;Gonzalez et al 1993;Mursula & Zieger 1998;Prabhakaran Nayar et al 2001Svalgaard & Wilcox 1975). Temmer et al (2007) also linked the 9 day timescale to coronal hole variability in the declining phase of solar cycle 23, by comparing coronal hole areas with daily averages of solar wind parameters, speed, density, temperature, and IMF magnitude.…”

Section: Introductionmentioning

confidence: 92%

COHERENT STRUCTURE IN SOLAR WIND C^{6 +}/C^{4 +}IONIC COMPOSITION DATA DURING THE QUIET-SUN CONDITIONS OF 2008

Edmondson

Lynch

Lepri

et al. 2013

ApJ

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This analysis offers evidence of characteristic scale sizes in solar wind charge state data measured in-situ for thirteen quiet-sun Carrington rotations in 2008.Using a previously established novel methodology, we analyze the wavelet power spectrum of the charge state ratio C 6+ /C 4+ measured in-situ by ACE/SWICS for 2-hour and 12-minute cadence. We construct a statistical significance level in the wavelet power spectrum to quantify the interference effects arising from filling missing data in the time series (Edmondson et al. 2013), allowing extraction of significant power from the measured data to a resolution of 24 mins. We analyze each wavelet power spectra for transient coherency, and global periodicities resulting from the superposition of repeating coherent structures. From the significant wavelet power spectra, we find evidence for a general upper-limit on individual transient coherency of ∼10 days. We find evidence for a set of global periodicities between 4-5 hours and 35-45 days. We find evidence for the distribution of individual transient coherency scales consisting of two distinct populations. Below the ∼2 day time scale the distribution is reasonably approximated by an inverse power law, whereas for scales 2 days, the distribution levels off showing discrete peaks at common coherency scales. In addition, by organizing the transient coherency scale distributions by wind type, we find these larger, common coherency scales are more prevalent and well-defined in coronal hole wind. Finally, we discuss the implications of our results for current theories of solar wind generation and describe future work for determining the relationship between the coherent structures in our ionic composition data and the structure of the coronal magnetic field.

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Cited by 31 publications

References 16 publications

A multiyear (2002–2006) climatology of O/N₂ in the lower thermosphere from TIMED GUVI and ground‐based photometer observations

A multiyear (2002–2006) climatology of O/N₂ in the lower thermosphere from TIMED GUVI and ground‐based photometer observations

Analysis of High Cadence in Situ Solar Wind Ionic Composition Data Using Wavelet Power Spectra Confidence Levels

COHERENT STRUCTURE IN SOLAR WIND C^{6 +}/C^{4 +}IONIC COMPOSITION DATA DURING THE QUIET-SUN CONDITIONS OF 2008

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Untitled

Cited by 31 publications

References 16 publications

A multiyear (2002–2006) climatology of O/N2 in the lower thermosphere from TIMED GUVI and ground‐based photometer observations

A multiyear (2002–2006) climatology of O/N2 in the lower thermosphere from TIMED GUVI and ground‐based photometer observations

Analysis of High Cadence in Situ Solar Wind Ionic Composition Data Using Wavelet Power Spectra Confidence Levels

COHERENT STRUCTURE IN SOLAR WIND C6 +/C4 +IONIC COMPOSITION DATA DURING THE QUIET-SUN CONDITIONS OF 2008

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A multiyear (2002–2006) climatology of O/N₂ in the lower thermosphere from TIMED GUVI and ground‐based photometer observations

A multiyear (2002–2006) climatology of O/N₂ in the lower thermosphere from TIMED GUVI and ground‐based photometer observations

COHERENT STRUCTURE IN SOLAR WIND C^{6 +}/C^{4 +}IONIC COMPOSITION DATA DURING THE QUIET-SUN CONDITIONS OF 2008