# MODIS Cloud Detection Evaluation Using CALIOP over Polluted Eastern China
## 3 Results and Discussion
### The Contributions of Different Cloud Phases to Discrepancies between MODIS and CALIOP  
The variation of the proportion of different cloud phases with SZA showed that the proportion of water cloud increased with an increase in SZA within 20-60\({}^{\circ}\) and decreased slightly at SZA \(>\) 60\({}^{\circ}\), while the proportion of ice cloud decreased with an increase in SZA and that of undetermined-phase cloud increased with an increase in SZA (Figure 6a). The consistency between MODIS and CALIOP was the largest for ice cloud, followed by undetermined-phase cloud, and the consistency was the smallest for water cloud (Figure 6b-d), with the average consistent percentages of 85%, 67%, and 41% over all SZA for ice, undetermined-phase, and water clouds, respectively. Over the three surfaces, the proportion of consistency between MODIS and CALIOP was high at SZA \(<\) 35\({}^{\circ}\). The consistent percentage increased a little bit within 35-60\({}^{\circ}\) SZA over dark and water surfaces. At higher SZA (\(>\)60\({}^{\circ}\)), the consistent percentage decreased to lower than that at SZA \(<\) 35\({}^{\circ}\) over the three surfaces.  
MODIS and CALIOP observed consistent ice cloud over the three surfaces for different SZA. The consistent percentage of ice cloud observed by MODIS and CALIOP was almost larger than 75%, and the percentage observed by MODIS alone was less than 3%, except at high SZA (\(>\)64\({}^{\circ}\)) for dark and water surfaces. The consistent percentage of undetermined-phase cloud observed by MODIS and CALIOP was almost larger than 60% and the percentage observed by MODIS alone was less than 7% at low SZA (\(<\)58\({}^{\circ}\), 54\({}^{\circ}\), and 60\({}^{\circ}\) over dark, bright, and water surfaces, respectively). MODIS and CALIOP observed relatively weak consistent water cloud. The consistent proportion of water cloud observed by MODIS and CALIOP was within the range of 40% to 64%, 30% to 58%, and 37% to 67% at low SZA  
Figure 6: **(a)** The proportion of MODIS cloud phases (water cloud, ice cloud, and undetermined-phase cloud); **(b–d)** The proportion of water, ice, and undetermined-phase clouds over dark, bright, and water surfaces, respectively. Solid lines show the consistent proportion observed by both MODIS and CALIOP, and dashed lines show the non-consistent proportion observed by MODIS alone.  
over dark, bright, and water surfaces, respectively. The percentage of water cloud observed by MODIS alone exceeded the consistent percentage at SZA \(>\) 58\({}^{\circ}\), 38\({}^{\circ}\), and 62\({}^{\circ}\) over dark, bright, and water surfaces, respectively. The percentage of water cloud observed by MODIS alone increased to amounts as high as 73%, 83%, and 98% at high SZA, while the consistent proportion could be as low as 13%, 2%, and 0% over dark, bright, and water surfaces, respectively. This increase in MODIS detection of water clouds at high SZA is consistent with our earlier analysis where MODIS detects more low-level clouds than CALIOP in general (Figure 2a), and this bias is greatest at highest SZA (Figure 3).