Mitchell Kirshner, University of Arizona; Eric C. Pearce, University of Arizona; Harrison Krantz, University of Arizona; Adam Block, University of Arizona
Keywords: Cislunar SSA, Sky Brightness, Photometry, Volcanism
Abstract:
On January 15th 2022, the submarine volcano Hunga Tonga–Hunga Ha?apai erupted and released an ash plume which reached the stratosphere. This is the largest eruption witnessed since the eruption of Mount Pinatubo in the Philippines in 1991, which famously cooled global temperatures due to the injection of volcanic aerosols into the stratosphere. Although much research studies the climatological impacts of large volcanic eruptions in which ash plumes reach the stratosphere, considerably less research exists on the impact of the inclusions of these new aerosols on night sky brightness and the impact to ground based optical telescope performance. Increased sky brightness due to volcanic aerosols can degrade optical capabilities significantly, especially when performing cislunar SSA in moonlight. Furthermore, modeling the impact of fresh volcanic aerosols is problematic, as radiative transfer modeling software such as MODTRAN generalizes volcanic ash and neglects considerations of specific plume properties; the same is true of astronomical models’ considerations of stratospheric volcanic ash.
While the recent Hunga Tonga eruption did not eject nearly as much material into the stratosphere as Mt. Pinatubo, satellites and ground-based instruments recorded an unprecedented amount of data which allows for comprehensive analysis of the eruption’s plume, and by extension it’s impact on ground-based optical SSA. Current optical instrument performance is designed to meet sensitivity requirements of a dark sky with little margin of error, so even small increases to night sky brightness due to aerosols could disrupt SSA coverage, particularly for cislunar space. This work begins with an overview of stratospheric volcanic aerosols and their impact on optical instruments and SSA, followed by a summarization of satellite and ground-based measurements of the Hunga-Tonga eruption specifically pertaining to fresh volcanic aerosol stratospheric injection and diffusion. These measurements include data from the following instruments: NOAA’s GOES-West satellite, NASA’s CALIPSO mission, ESA’s Copernicus Sentinel-5P mission, balloon-borne in-situ measurements made by an international collaboration of researchers, and AERONET which makes use of CIMEL photometers. This data is compared to a literature review of historical published information about the introduction of volcanic ash into the stratosphere by Mount Pinatubo in 1991.
Additionally, this study considers the night sky brightness in Tucson, Arizona using the University of Arizona’s Pomenis Observatory for the nights following the eruption of Hunga-Tonga, providing sufficient time for the plume’s stratospheric aerosols to travel globally. These night sky brightness measurements are compared to theoretical results derived from MODTRAN simulations as well as past results at similar lunar illuminations and photometric conditions to identify potential impacts of Hunga-Tonga’s stratospheric aerosols on cislunar SSA. Relevant values and plots are presented demonstrating this comparison, and differences between night sky brightness measurements are presented. Discussion of results emphasizes the need to consider unpredictable explosive volcanic eruptions in planning national and international cislunar SSA to improve resiliency of cislunar object tracking. Recommendations for the SSA community stemming from this research include advancing plume tracking research to better understand impact on ground-based optical instruments as large stratospheric ash plumes disperse over time and utilizing information of stratospheric plume chemical composition to improve stratospheric radiative transfer models from that data.
Date of Conference: September 27-20, 2022
Track: Atmospherics/Space Weather