Spatial-scale dependence of aerosol indirect effects over land in eastern China: a comparative analysis

Abstract. Regulatory effects of liquid water path (LWP) on cloud droplet effective radius (CER) and the interaction between aerosol optical depth (AOD) and cloud properties were systematically investigated. MODIS and CALIOP observed aerosols and clouds over eastern China in two periods: 2008–2014 (period 1) and 2015–2022 (period 2). The results show two distinct regimes of the variation of CER with LWP: a rapid growth regime (LWP < 55/50 g/m²) and a decreasing regime (LWP = 55–135/50–100 g/m²) (thresholds vary by period). The sensitivity of CER to AOD (SCER) shows a negative correlation, and the SCER in the LWP regime 2 shows larger than that in LWP regime 1. Here, the spatial scale is described by buffer size and study area. Overall, |SCER| decreases with increasing spatial scale. The optimal buffer sizes show notable variations in the range from 6°×6° to 10°×10°: increasing as study areas increase in period 2, but decreasing in period 1 for LWP regime 2. Compared with period 1, |SCER| in period 2 exhibits significantly decreases, reflecting the weaker of aerosol-cloud interactions for declining aerosol concentrations. Additionally, the sensitivity of Nd (cloud droplet number concentration) to AOD (SNd) shows a positive correlation, with SNd decreases as spatial scale increases. The optimal buffer sizes show larger in the 8°×8° and 10°×10° regions than that in the 4°×4° and 6°×6° areas. This study reveals the scale-dependence of aerosol-cloud interactions.