Trace gas measurements from air samples collected weekly at a globally distributed network of sampling sites revealed sharp increases in the growth rates of CH4 and CO in the tropics and high southern latitudes immediately following the eruption of Mt. Pinatubo on June 15, 1991. The eruption emitted ∼20 Mt SO2 into the lower stratosphere. Calculations made with a radiative transfer model show that UV actinic flux in the wavelength region 290–330 nm was attenuated by ∼12% immediately after the eruption due to direct absorption by SO2, and that it was perturbed for up to 1 year after the eruption due to scattering by sulfate aerosols. We suggest that the decreased UV flux decreased the steady‐state [OH] and led to the observed anomalously large growth rates for CH4 and CO during late‐1991 and early‐1992.

The Second Wind Forecast Improvement Project (WFIP2) is a U.S. Department of Energy (DOE)- and National Oceanic and Atmospheric Administration (NOAA)-funded program, with private-sector and university partners, which aims to improve the accuracy of numerical weather prediction (NWP) model forecasts of wind speed in complex terrain for wind energy applications. A core component of WFIP2 was an 18-month field campaign that took place in the U.S. Pacific Northwest between October 2015 and March 2017. A large suite of instrumentation was deployed in a series of telescoping arrays, ranging from 500 km across to a densely instrumented 2 km × 2 km area similar in size to a high-resolution NWP model grid cell. Observations from these instruments are being used to improve our understanding of the meteorological phenomena that affect wind energy production in complex terrain and to evaluate and improve model physical parameterization schemes. We present several brief case studies using these observations to describe phenomena that are routinely difficult to forecast, including wintertime cold pools, diurnally driven gap flows, and mountain waves/wakes. Observing system and data product improvements developed during WFIP2 are also described.