During Biogenic Aerosols—Effects on Clouds and Climate (BAECC), the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Program deployed the Second ARM Mobile Facility (AMF2) to Hyytiälä, Finland, for an 8-month intensive measurement campaign from February to September 2014. The primary research goal is to understand the role of biogenic aerosols in cloud formation. Hyytiälä is host to the Station for Measuring Ecosystem–Atmosphere Relations II (SMEAR II), one of the world’s most comprehensive surface in situ observation sites in a boreal forest environment. The station has been measuring atmospheric aerosols, biogenic emissions, and an extensive suite of parameters relevant to atmosphere–biosphere interactions continuously since 1996. Combining vertical profiles from AMF2 with surface-based in situ SMEAR II observations allows the processes at the surface to be directly related to processes occurring throughout the entire tropospheric column. Together with the inclusion of extensive surface precipitation measurements and intensive observation periods involving aircraft flights and novel radiosonde launches, the complementary observations provide a unique opportunity for investigating aerosol–cloud interactions and cloud-to-precipitation processes in a boreal environment. The BAECC dataset provides opportunities for evaluating and improving models of aerosol sources and transport, cloud microphysical processes, and boundary layer structures. In addition, numerical models are being used to bridge the gap between surface-based and tropospheric observations.

Boreal forest acts as a carbon sink and contributes to the formation of secondary organic aerosols via emission of aerosol precursor compounds. However, these influences on the climate system are poorly quantified. Here we show direct observational evidence that aerosol emissions from the boreal forest biosphere influence warm cloud microphysics and cloud-aerosol interactions in a scale-dependent and highly dynamic manner. Analyses of in-situ and ground-based remote sensing observations from the SMEAR II station in Finland, conducted over eight months in 2014, reveal significant increases in aerosol load over the forest one to three days after aerosol-poor marine air enters the forest environment.We find that these changes are consistent with secondary organic aerosol formation and, together with water vapor emissions from evapotranspiration, are associated with changes in the radiative properties of warm, low-level clouds. The feedbacks between boreal forest emissions and aerosol-cloud interactions and the highly dynamic nature of these Petäjä et al. (2021) Influence of biogenic emissions from boreal forests on aerosol-cloud-interactions, Nature Geosci. (accepted)

This paper illustrates a key lesson related to most uses of long‐range climate forecast information, namely that effective weather‐related decision‐making requires understanding and integration of weather information with other, often complex factors. Northern Illinois University's heating plant manager and staff meteorologist, along with a group of meteorology students, worked together to assess different types of available information that could be used in an autumn natural gas purchasing decision. Weather information assessed included the impact of ENSO events on winters in northern Illinois and the Climate Prediction Center's (CPC) long‐range climate outlooks. Non‐weather factors, such as the cost and available supplies of natural gas prior to the heating season, contribute to the complexity of the natural gas purchase decision. A decision tree was developed and it incorporated three parts: (a) natural gas supply levels, (b) the CPC long‐lead climate outlooks for the region, and (c) an ENSO model developed for DeKalb. The results were used to decide in autumn whether to lock in a price or ride the market each winter. The decision tree was tested for the period 1995–99, and returned a cost‐effective decision in three of the four winters. Copyright © 2000 Royal Meteorological Society

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Abstract. The Peak Design Ltd hyperspectral radiometer (HSR1) was tested at the Atmospheric Radiation Measurement User Facility (ARM) Southern Great Plains (SGP) site in Lamont, Oklahoma for two months from May to July 2022. The HSR1 is a prototype instrument that measures total and diffuse spectral irradiance from 360 to 1100 nm with a spectral resolution of 3 nm. The HSR1 spectral irradiance measurements are compared to nearby collocated spectral radiometers including two multifilter rotating shadowband radiometers (MFRSR) and a shortwave array spectroradiometer—hemispheric (SASHe). The total spectral irradiances at 500 nm for the HSR1 compared to the MFRSRs have a mean (relative) difference of 0.01 W m-2 nm-1 (1–2 %). The HSR1 mean diffuse spectral irradiance at 500 nm is smaller than the MFRSRs by 0.03–0.04 (10 %) W m-2 nm-1. The HSR1 clear-sky aerosol optical depth (AOD) is also retrieved by considering Langley regressions and compared to collocated instruments such as the Cimel sunphotometer (CSPHOT), MFRSRs, and SASHe. The mean HSR1 spectral AOD at 500 nm is larger than the CSPHOT by 0.010 (8 %) and larger than the MFRSRs by 0.007–0.017 (6–18 %). In general, good agreement between the HSR1 and other instruments is found in terms of the spectral total irradiance, diffuse irradiance, and AODs at 500 nm. The HSR1 quantities are also compared at other wavelengths to the collocated instruments, where similar agreement is found for the spectral irradiances, although relatively larger disagreement is found at higher wavelengths, especially for spectral AODs.