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 pioneering study elucidates the long-term trends and intricate variability of the radiative impacts and optical characteristics of cirrus clouds over two decades, from 2003 to 2022 at the NASA GSFC in Greenbelt, Maryland, USA, headquarters of the Micropulse Lidar Network (MPLNET) project. Over twenty years, analysis of the net cloud radiative effects (CREs) at both the top-of-the-atmosphere (TOA) and surface (SFC) reveals decreases in radiative flux by -0.0017 and -0.0035 W m^-2 yr^-1 and -0.0027 and -0.048 W m^-2 yr^-1, respectively (based on the constrained solutions for lidar-derived 523/527/532 nm extinction coefficient (m^-1) solved for lidar ratios bounded by both 20 and 30 sr). Concurrently, pivotal attributes such as cloud boundary temperature and altitude and integrated optical depth exhibit noteworthy stability, punctuated only by minor seasonal shifts. 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 decline in radiative flux at both the TOA and SFC can be perceived as a positive feedback loop that leads to increased atmospheric warming. The unveiled trends underscore the intricate synergy between albedo, radiative flux, and climate dynamics, pressing the need for vigilant monitoring of these shifts, given their profound implications for future climatic and circulatory phenomena.