Daytime Cirrus Cloud Radiative Forcing from MPLNET Lidar Measurements during 2010 and 2011 at Singapore Observational Site

We estimate daytime cirrus cloud radiative forcing (CRF) from ground-based lidar observations at Singapore in 2010 and 2011. Estimates are derived both over land and water to simulate conditions over the broader Maritime Continent archipelago of Southeast Asia. The relative daytime TOA CRF is estimated at about 2.858 - 3.370 W/m2 in 2010 (both 20/30 sr, respectively) and 3.078 - 3.329 W/m2 in 2011, and over ocean between -0.094 - 0.541 W/m2 in 2010 and -0.598 - 0.433 W/m2 in 2011. After normalizing these estimates for an approximately 80% local satellite-estimated cirrus cloud occurrence rate, they reduce in absolute terms to 2.198 - 2.592 W/m2 in 2010 and 2.368 - 2.561 W/m2 in 2011 over land, and -0.072 - 0.416 W/m2 in 2010 and - 0.460 - 0.333 W/m2 in 2011 over ocean. These annual estimates are mostly consistent despite a tendency toward lower relative cloud top heights in 2011. These estimates strength the open hypothesis of a meridional hemispheric gradient in cirrus cloud daytime TOA CRF globally, varying from positive near the equator to presumably negative approaching the non-ice covered poles. They help expand upon the paradigm, however, conceptualizing differences zonally between over-land and overwater forcing that differs significantly. More of the global oceans are likely subject to negative daytime TOA CRF than previously implied.