DOI: 10.5281/zenodo.17539352
title: PSP Ion-scale Circularly Polarized Wave Repository

description: The repository documents the ion-scale circularly polarized waves observed by the Parker Solar Probe (PSP) at perihelia during its prime science phase, i.e.,  the first 24 encounters. Ion-scale waves are identified by using PSP/FIELDS MAG L2 magnetic field RTN time series as described in Niranjana et al. 2023 and 2024 (NKM23, 24). The magnetic field time series of all encounters is split into continuous 15-minute intervals and the following routine is applied on each interval:  (a) the reaction-wheel noise is identified and removed (Appendix B.1 of NKM23), (b) the time series is downsampled to a frequency at which magnetic energy spectra hits the MAG noise floor, (c) the spectrum of circular polarization of magnetic field fluctuations in the spacecraft frame is evaluated as a function of frequency and time using Mortlet wavelet transforms (Appendix B.3. of NKM23), and (d) a time smoothening routine is applied on the polarization spectra to distinguish the region in frequency-time space with persistent high values of circular polarization corresponding to ion-scale waves. Using the ion-scale wave frequency-time region of all intervals, the times and frequencies at which left-handed (LH) and right-handed (RH) waves occur are identified. 

The repository contains two types of files: (a) E[n]_wave_presence_ind.h5, (b) E[n]_distinct_waves_noise_accounted.h5 or E[n]_distinct_waves.h5. Here n is the encounter number. The files are in HDF5 format and can be read in Python using the pandas module. Pandas can be imported into a Python script, and an HDF5 file can be read by 

import pandas as pd
pd.read_hdf('filename.h5')

The E[n]_wave_presence_ind.h5 files document the presence and absence of ion-scale waves as a function of time for the nth encounter. The time bin widths of these files vary between the set of time increments, [1/8, 1/4, 1/2, 1] New York seconds (NYs), where 1NYs = 0.8738 s. The files have the following columns as a function of time: 'LH', 'RH', 'cadence', as well as 'epoch'. The value of the 'LH'/'RH' column is: 0 if no LH/RH ion-scale wave is identified in that time bin; 1 if an LH/RH ion-scale wave is identified in at least one frequency bin at that time bin. The 'cadence' column is the bin width of the time bins.

The E[n]_distinct_waves_noise_accounted.h5 or E[n]_distinct_waves.h5 files document the frequency bands at which LH and RH waves are observed for continuous 5-minute intervals of the nth encounter. The files have the following columns: 'int', 'sub_int', 'LH', 'RH', 'start time', and 'end time'. The 'LH' and 'RH' columns further have two sub-columns, 'lower freq' and 'upper freq'. The 'int' column is the index of the larger 15-minute interval. The 'sub_int' column is the index of the three 5-minute sub-intervals within a 15-minute interval. The 'lower freq' and 'upper freq' sub-columns of the 'LH' column are the lower and upper frequencies, respectively, of the frequency bands at which LH waves are observed within each 5-minute sub-interval. Similarly 'RH' column documents the frequency bands at which RH waves are observed within each 5-minute sub-interval. The 'start time' and the 'end time' are the start and end times of each 5-minute sub-interval. The 'lower freq' and 'upper freq' are Nans if no ion-scale waves are observed in that sub-interval. Note that a single broadband LH/RH ion-scale wave can be identified here as multiple LH/RH ion-scale waves with narrow frequency bands when waves are of lower amplitude compared to turbulent fluctuations. Moreover, the reaction-wheel noise removal routine can identify narrow frequency noise bands within an ion-scale wave frequency band, leading to its erroneous identification as multiple narrow-band waves. We have tried to correct for such erroneous identification due to the application of the noise-removal routine for Encounter 3 onwards, with filenames E[n]_distinct_waves_noise_accounted.h5. In Encounters 1 and 2, with filenames E[n]_distinct_waves.h5,  the reaction wheel noise frequency band usually does not overlap with the ion-scale wave frequency band, and hence no correction has been applied for these encounters. If the reader is interested in studying the possible multiple simultaneous waves with a better time resolution, they are advised to evaluate the spectrum of the spacecraft frame circular polarization of magnetic field fluctuations for the time interval of interest without applying the noise removal routine used here.