Mixing layer height (MLH) is a crucial parameter for air quality modelling that is still not routinely measured. Common methods for MLH determination use atmospheric profiles recorded by radiosonde but they suffer from course temporal resolution since balloon launching is only twice a day. Recently cheap ceilometers are gaining popularity in the retrieval of MLH diurnal evolution based on aerosol profiles. This study presents a comparison of a proprietary (Jenoptik) and a free available (STRAT) algorithms to retrieve MLH diurnal cycle. The comparison is accomplished in summer season over urban area and radiosonde data is used to estimate MLHs according to parcel, lapse rate, and Richardson methods (the last algorithm is used as a reference in the study) in addition. It was found that STRAT and Jenoptik give lower MLH than radiosonde with an underestimation of about 150m and 650m respectively. Additionally, STRAT showed reasonable performance in tracking of MLH diurnal evolution. Daily MLH maximum of about 2000m was found in the late afternoon (18-19 LT). In contrast, Jenoptik algorithm showed more weaknesses, mainly attributed to its real-time operation and independent processing of a single profile. At night and during morning transition period, both lidar-based methods showed difficulties as MLH was often in the ceilometer’s incomplete overlapping zone so residual or advected aerosol layers aloft were misleadingly reported as mixing layer (ML).

Warm cloud-precipitation plays a vital role in the hydrological cycle, weather, and climate. Comprehensive observation and study of warm cloud-precipitation can advance our understanding of the internal physical processes and provide valuable information for developing the numerical models. This paper mainly focused on a study of characteristics of warm cloud-precipitation in South China during the pre-flood season using datasets observed from a Ka-band cloud radar, laser ceilometer and disdrometer. Eighteen kinds of quantities from these three instruments were used to precisely elucidate the distribution, diurnal variation, vertical structure, and physical property of warm cloud-precipitation. The results showed that the occurrence of aloft cloud-precipitation decreased with the increase of height, and most of the hydrometeors were distributed below 2 km. During the observation period, the ground rainfall mainly came from light precipitation; however, short-time and sharp showers contributed to the majority of rain amounts. Most of the cloud layers were single-layer, with base heights below 2.2 km, thickness thinner than 2.1 km, and top heights within 0.6-4.2 km. Warm cloud-precipitation owned certain diurnal variations, with a rising trend of cloud base heights in the afternoon and midnight. During 0230-1100, 1200-1800, and 2100-2300, the convections were relatively active with higher cloud tops, thicker cloud thickness, and higher rainfall occurrences. Separation and statistical results of cloud and precipitation indicated that they owned different vertical structures and physical properties, exhibiting different value ranges and changes of radar reflectivity, vertical air motion, particle size, number concentration, liquid water, and rain rate at different height levels. The particle size distributions of cloud and precipitation both were exponential. Radar-derived raindrop size distribution was very coherent with the ground measurement when the reflectivity of precipitation was within 10-20 dBZ. However, for other reflectivity regimes, instrument sensitivity, sampling height, attenuation, and non-precipitating weak targets can affect the comparison.

The planetary boundary layer height (PBLH) is one of the key factors in influencing the dispersion of the air pollutants in the troposphere and hence the air pollutant concentration on ground level. For this reason, accurate air pollutant concentration depends on the performance of PBLH prediction. Recently, ceilometer, a lidar instrument to measure cloud base height, has been used by atmospheric scientists and air pollution control authorities to determine the mixing level height (MLH) in improving forecasting and understanding the evolution of aerosol layers above ground at a site. In this study, ceilometer data at an urban (Lidcombe) and a rural (Merriwa) location in the New South Wales, Australia was used to validate the PBLH prediction from two air quality models (CCAM-CTM and WRF-CMAQ) as well as to understand the aerosol transport from sources to receptor point at Merriwa for the three case studies where high PM10 concentration was detected in each of the three days. The results show that the PBLH prediction by the two air quality models corresponds reasonably well with observed ceilometer data and the cause and source of high PM10 concentration at Merriwa can be found by using ceilometer MLH data to corroborate with back trajectory analysis of transport of aerosols to the receptor point at Merriwa. Of the three case studies, one had aerosol source from north and north west of Merriwa in remote NSW where windblown dust is the main source, and the other two had sources from south and south east of Merriwa where anthropogenic sources dominate,