Code and Data for Article: FHD: An Extended Disturbance Storm-Time Index Based on Fitted Functions of Horizontal Geomagnetic Field Variation

Code Availability The complete computational framework and visualization tools used in this study are provided as supplementary materials: 1. figures_code.zip Content: Visualization and plotting scripts Description: Contains all Python scripts and functions used to generate the figures presented in this manuscript. The code includes data visualization routines, statistical analysis plots, and publication-quality figure generation scripts. Usage: Extract the archive and run the plotting scripts with the corresponding data files to reproduce all figures in the study. 2. dataDL&process.zip Content: Data download and processing pipeline Description: Contains the complete data acquisition and processing system for calculating the FHD index. This includes SuperMAG API interface modules, data quality control functions, Fourier series fitting algorithms, and the complete computational pipeline from raw geomagnetic station data to final FHD index values. Components: Data download scripts for SuperMAG geomagnetic station data Data processing and quality control modules Dst calculation and correction functions Fourier series fitting and parameter calculation Usage: Extract the archive and follow the provided README instructions to download, process, and calculate FHD indices from SuperMAG data. Both code packages are designed to ensure full reproducibility of the research results and can be used independently or in combination with the provided FHD index dataset. Data Description FHD Index Dataset Structure The FHD (Fourier Harmonic Disturbance) index dataset is organized by year and month, with each folder following the naming convention FHD-YYYYMM (e.g., FHD-200812 for December 2008). File Contents and Descriptions 1. df_results_mlat50.csv Content: FHD_global index values for the corresponding month Description: This file contains the global FHD index calculated using the Fourier series fitting method. The index represents the symmetric disturbance in the horizontal component of the Earth's magnetic field, derived from low-latitude geomagnetic stations (magnetic latitude ≤ 50°). The data provides minute-by-minute resolution of geomagnetic activity. Format: CSV file with columns: DATE: Timestamp in YYYY-MM-DD HH:MM:SS format FHD_global: Global FHD index values in nT (nanotesla) 2. mat_fit_paras_mlat50.csv Content: Fourier series fitting parameters Description: This file contains the Fourier series fitting parameters that can be used to reconstruct all FHD_mlt index family members. These parameters enable the generation of magnetic local time (MLT) dependent FHD indices, providing a complete characterization of the geomagnetic disturbance pattern as a function of local time. Format: CSV file with columns: DATE: Timestamp in YYYY-MM-DD HH:MM:SS format Parameter_columns: Various Fourier series coefficients and fitting parameters for each time point 3. over_fit_list - 2.csv Content: Over-fitted station information Description: This file contains information about stations that exhibited over-fitting characteristics during the Fourier series analysis. These stations were identified through quality control procedures and may have been excluded from the final FHD index calculation to ensure data reliability. Format: CSV file containing station codes and over-fitting criteria 4. station_avaliable_df_v2.csv Content: Final station information used in index calculation Description: This file contains comprehensive information about all stations that were ultimately included in the FHD index calculation. It includes station metadata such as geographic coordinates, geomagnetic coordinates, data quality metrics, and availability flags. Format: CSV file with columns: Station codes as index glon, glat: Geographic longitude and latitude mlon, mlat: Geomagnetic longitude and latitude NaNprop: Proportion of missing data Additional quality control parameters Data Coverage The dataset spans from December 2008 to April 2024, providing continuous coverage of geomagnetic activity over approximately 15.5 years. Each monthly folder contains the complete set of files necessary for both the global FHD index and the reconstruction of MLT-dependent index variations. Quality Control The dataset incorporates multiple levels of quality control: Station selection based on magnetic latitude criteria (≤ 50°) Data completeness verification Over-fitting detection and station removal Fourier series fitting quality assessment This comprehensive dataset enables researchers to analyze both global geomagnetic activity patterns and their local time dependencies, providing valuable insights into space weather phenomena and their temporal characteristics.