Long-Term and Short-Term Space Weather Phenomena Observed By VIIRS Day/Night Band

The Day/Night Band (DNB) of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard Suomi-NPP (SNPP), NOAA-20 and NOAA-21 satellites is a major advancement in nighttime light imaging capability. VIIRS DNB detects radiances spanning 7 orders of magnitude in one panchromatic (0.5-0.9 μm) band and provides nighttime imagery of clouds, nocturnal lights, and aurora, with a spatial resolution of ~750 m across the scan. This study demonstrates the unique capabilities of VIIRS DNB in observing space weather phenomena and highlights the ability to monitor the drift of the South Atlantic Anomaly (SAA) and quantifying aurora light emissions during geomagnetic storms. In the study of SAA drift, sporadic bright pixels contaminating the nighttime DNB imagery during orbital passes over the South Atlantic region are attributed to energetic particles which penetrate into the VIIRS instrument. The electric signals induced by the energetic particles originating from the radiation belt on the DNB CCD detector array are registered as incident photons, thus providing a serendipitous monitoring capability. The long-term records of locations and radiance values of the bright pixels over the South Atlantic region in SNPP DNB data since 2012 are compiled for analyzing the spatial distribution and temporal evolution of the SAA. The DNB radiance data are used to obtain the SAA centroids, i.e., the peaks of the energetic particle distribution for each year. The data show the longitudinal drift of SAA to be westward and the rate computed from this analysis is 0.323 deg/yr. This drift rate is higher than those obtained from DMSP (F8 – F18) data for 1988 to 2015, which corresponds to the ascending phase of Solar Cycle 22 to the peak of Cycle 24. In another application of DNB observations of space weather, the spatial distribution and temporal evolution of visible aurora during the two recent severe geomagnetic storms (March and April2023) are analyzed. The radiance data of the night sides in both hemispheres during the two events are used to analyze the spatial structure of aurora for each orbital pass from radiance contours. The evolution of aurora is quantitatively characterized with time series of the poleward and low latitude boundary of aurora, their latitude-range and area, peak radiance and total light emission of the aurora region in the DNB observation. These characteristic parameters are correlated with solar wind variables and the geomagnetic aurora electrojet index. The VIIRS DNB onboard three NOAA satellites will provide unprecedented data of the ascending phase of Solar Cycle 25 for analyzing the aurora, SAA and other space weather phenomena.