Long-term trends in daytime cirrus cloud radiative effects: analyzing twenty years of Micropulse Lidar Network measurements at Greenbelt, Maryland in eastern North America

Abstract. This study analyzes a 20-year dataset (2003–2022) to understand long-term trends in radiative effects and optical properties of cirrus clouds. The research was conducted at NASA's Goddard Space Flight Center in Greenbelt, Maryland, USA, the primary location of the Micropulse Lidar Network (MPLNET) project. Analysis of net cloud radiative effects (CREs) at both the top-of-the-atmosphere (TOA) and surface (SFC) reveals decreases in radiative flux by −0.019 and −0.037 W m−2 yr−1 and −0.031 and −0.068 W m−2 yr−1, respectively, based on constrained solutions for lidar-derived 523/527/532 nm extinction coefficient (m−1) solved for lidar ratios bounded by 20 and 30 sr. Currently, key cloud properties such as boundary temperature and altitude, as well as integrated optical depth, remained stable with only minor seasonal changes. This study also uncovers a persistent decline in surface albedo, with a derived trend of −0.00036 yr−1. We further find that the interrelationship between CRE and surface albedo variation intensifies notably during winter months. This leads to speculation that a decrease in the number of days of snow and ice is the main driver of the decrease in surface albedo. The observed trends show a complex relationship between albedo, radiative flux, and climate, highlighting the need for continued monitoring due to their significant impact on future climate and weather patterns. We further quantify trend uncertainty with block-bootstrapped 95 % confidence intervals and evaluate sensitivity to solar zenith angle (SZA), finding that TOA trend magnitudes are partially explained by increasing SZA while surface trends remain robust.