Air Pollution Remote Sensing and the Subsequent Interactions with Ecology on Regional Scales

The increasing trend in drought events under the background of global warming makes it more important to understand the drought effect on vegetation photosynthesis. While diverse global gross primary production (GPP) datasets were adopted to investigate the drought impact on photosynthesis, few studies focused on the discrepancies of drought response among different GPP datasets, especially for the cumulative drought impact. Therefore, a total of twenty-six global GPP datasets based on process, machine learning (ML), and light-use efficiency (LUE) model schemes were obtained to appraise the cumulative impact of drought stress on photosynthesis from 2001 to 2010. Moreover, a relatively reliable global pattern of drought’s cumulative effect on vegetation photosynthesis was acquired from these global GPP products through probability analysis. The results illustrated that the cumulative impact of drought existed in 52.11% of vegetation cover land with the cumulative time scales dominantly at a short term (1–4 months, 31.81%). Obvious heterogeneity of the drought cumulative effect in space and different vegetation functional types was observed, as the reliability of the drought effect decreased with latitude decreasing and a higher sensitivity to drought in herbaceous vegetation than woody plants. Our findings highlighted the importance of ways in characterizing moisture conditions across vegetation types among various GPP models and the necessity of GPP dataset selection in investigating drought effect on photosynthesis.

On November 29, 2019, an aircraft observation during the period of cloud-seeding was carried out for a mixed-phase cloud over Xingtai, Hebei Province, China. This study investigates the response of mixed-phase cloud microphysical properties to cloud-seeding near cloud top. Before cloud seeding, the cloud droplet concentration from fast cloud droplet probe (N_C__FCDP) presented a multi-peak vertical distribution structure, with a maximum concentration of 192 cm⁻³ at a height of 3,322 m; the maximum concentration of ice crystals from cloud imaging probe (N_C__CIP) was 10 L⁻¹, which appeared at 4,500 m in the upper part of cloud; and the peak value of liquid water content (LWC) in the cloud also appeared at 4,500 m, with a value of 0.15 g/m³. The coexistence of supercooled liquid water and ice crystals implies that they are particularly suitable for cloud seeding at the height of 4,550 m. About 7–8 min later after cloud seeding at this height, the average N_C__FCDP decreased from 160.3 to 129 cm⁻³, and the average N_C__CIP increased from 7.1 to 10 L⁻¹. Moreover, after cloud seeding, high N_C__CIP as well as larger and more ice crystals appeared almost in the same areas within the cloud, and LWC presented an obvious decreasing trend. In contrast, the concentration of small cloud droplets and LWC decreased obviously after seeding. The findings suggest that the cloud microphysical properties showed obvious responses to the artificial introduction of silver iodide, which is important for human weather modification.