Diurnal variation of heavy rainfall over the Beijing-Tianjin-Hebei region: Role of aerosol cloud ...

[Diurnal variation of heavy rainfall over the Beijing-Tianjin-Hebei region: Role of

aerosol cloud effect and its sensitivity to moisture](https://www.atmos-chem-phys-discuss.net/acp-2018-1072/)

我们最近的研究发现，在2002-2012年期间，京津冀地区暴雨的在清洁和污染环境之间呈现出不同的特征。我们将卫星云产品与气象和气溶胶数据结合起来，进一步检查气溶胶对云的影响，重点关注其对湿度的敏感性。在气溶胶浓度较高的时候，较早的起始时间，较早的高峰时段和较长的强降雨持续时间的特征通常伴随着云量的增加，云顶高度的增加/减少，液/冰有效半径的增加/减少。然而在较低和较高湿度下，气溶胶对云顶和液滴有效半径效应是不同的。与黑碳加热对流层低层并可能产生强降雨发生较早的辐射效应不同，气溶胶云效应提高了降水效率并提高了降雨峰值，这可能归因于云滴数和云水的增加，当背景水分供应充足时会增强碰撞 - 聚结和加速降雨形成。该推测需要进一步的数值实验来验证。

DATA

To study diurnal variation of rainfall, the gauge-based hourly precipitation datasets were used, which were obtained from the National Meteorological Information Center (NMIC) of the China Meteorological Administration (CMA) (Yu et al., 2007) at 2420 stations in China from 1951 to 2012.

** MACC-II (Monitoring Atmospheric Composition and Climate Interim Implementation) reanalysis product provided by ECMWF (the European Centre for Medium-Range Weather Forecasts), which assimilates total AOD retrieved by MODIS to correct for model departures from observed aerosols (Benedetti et al., 2009),provided the two-dimensional AOD and three-dimensional aerosol mass concentration datasets for different kinds of aerosols (BC, sulfate, organic matter, mineral dust and sea salt). MACC-II reanalysis products are observationally-based within a model framework, which can offer a more complete temporal and spatial coverage than observation and overcome the shortcoming of simulation that fail in simulating the complexity of real aerosol distributions. The horizontal resolution of MACC-II is 1°×1° and the vertical resolution is 60 levels. MACC-II data covers the period of 2003 to 2012, of which the time interval is six-hour**

Daily cloud variables, including cloud fraction (CF), cloud top pressure (CTP), cloud optical thickness (COT, liquid and ice), cloud water path (CWP, liquid and ice) and cloud effective radius (CER, liquid and ice), were obtained from MODIS Collection 6 L3 cloud product onboard the Terra satellite. The MODIS cloud product combines infrared emission and solar reflectance techniques to determine both physical and radiative cloud properties (Platnick et al., 2017). The validation of cloud top properties in this product has been conducted through comparisons with CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) data and other lidar estimates using aircraft observations, and the validation and quality control of cloud optical products is performed primarily using in situ measurements obtained during field campaigns as well as the MODIS Airborne Simulator (MAS) instrument (https://modis-atmos.gsfc.nasa.gov/products/cloud). Likewise, the quality assurance of marginal or higher confidence was used in this study

The three-dimensional cloud variables, such as CF, cloud liquid water and cloud ice water, were obtained from MERRA2 (the second Modern-Era Retrospective analysis for Research and Applications) reanalysis datasets. MERRA2 reanalysis data is undertaken by NASA for the satellite era using GEOS-5 (version 5 of the Goddard Earth Observing System Data Assimilation System), which is the first long-term global reanalysis to assimilate space-based observations of aerosols and represent their interactions with other physical processes in the climate system. The horizontal resolution is 0.624°x0.5° and the vertical resolution is 42 levels with three-hour intervals (Rienecker et al., 2008). Since the clouds associated with heavy rainfall in the BTH region during the early summer contain warm clouds, cold clouds and mixed-phase clouds (e.g. Guo et al., 2015), we purposely selected the clouds with its top pressure above 600 hPa because the 0℃ isotherm of BTH region is nearly located at this height.

PDF of (a) starting time (units: LST), (b) peak time (units: LST), (c) duration (units: hours) and (d) intensity (units: 0.1mm/hour) of heavy rainfall on selected clean (blue lines: AOD<0.98) and polluted (red lines: AOD>2.00) days, respectively, during early summers from 2002 to 2012.

Diurnal variation of cloud liquid water (units: mg/kg) respectively for (a) clean days, (b) polluted days and (c) difference (polluted minus clean), and cloud ice water (units: mg/kg) respectively for (d) clean days, (e) polluted days and (f) difference (polluted minus clean). Differences have passed 95% significant test.

The changes of CF (units: %), COT (liquid and ice, units: none), CWP (liquid and ice, units: g/m2 580 ) and CTP (units: hPa) along with the variation of the 850 hPa RH on selected clean (blue lines: AOD<0.98) and polluted (red lines: AOD>2.00) heavy rainfall days during 11 summers (2002-2012). The blue and red straight lines show the linear regressions. The trends have all passed the significant test of 95%.

A schematic diagram for aerosols impact on the diurnal variation of heavy rainfall over Beijing-Tianjin-Hebei region.