Long-term (1999-2019) variability of stratospheric aerosol over Mauna Loa, Hawaii, as seen by two co-located lidars and satellite measurements

As part of the Network for the Detection of Atmospheric Composition Change (NDACC), ground-based measurementsobtained from the JPL stratospheric ozone lidar and the NOAA stratospheric aerosol lidar at Mauna Loa, Hawaii over thepast two decades were used to investigate the impact of volcanic eruptions and pyro-cumulonimbus smoke plumes on thestratospheric aerosol load above Hawaii since 1999. Measurements at 355 nm and 532 nm conducted by these two lidarsrevealed Ångström exponents between -1.6 and -0.6 for background and smoke plumes, respectively. Measurements of theNabro plume by the JPL lidar in 2011/2012 showed a lidar ratio of (64.0+-12.7) sr at 355nm around the center of the plume.The new GloSSAC, CALIOP Level 3 and SAGE III-ISS stratospheric aerosol datasets were compared to the ground-basedlidar datasets. The intercomparison revealed a generally good agreement, with vertical profiles of extinction coefficient within 50% between 17 km and 23 km above sea level (ASL), and within 25% above 23 km ASL. The stratospheric aerosol depthderived from all these datasets shows good agreement, with the largest discrepancy (20%) being observed between the newCALIOP Level 3 and the other datasets. All datasets consistently reveal a relatively quiescent period between 1999 and 2005,followed by an active period of multiple eruptions (e.g., Nabro) until early 2012. Another quiescent period, with slightly higheraerosol background, lasted until mid-2017, when a combination of extensive wildfires and multiple volcanic eruptions caused a significant increase in stratospheric aerosol loading. This loading maximized at the very end of the time period considered(fall 2019) as a result of the Raikoke eruption, the plume of which ascended to 26 km altitude in less than three months.