# First Observations of Cirrus Clouds Using the UZ Mie Lidar over uMhalthuze City, South Africa
## 4 Results and Discussion
This cirrus cloud is classified as a dense cirrus cloud with COD values ranging from 1.48 to 1.70 (see Figure 4b). Unlike the cirrus cloud observed on 10 April 2019, the trend of the COD was observed to be upwards, with minimum values of approximately 1.48 at the beginning of the time series and maximum values of approximately 1.70 towards the end of the time series. The extinction coefficient vertical profile of the enhancement of the extinction coefficient at the height between 1 and 2 km and between 9.5 and 12 km due to the presence of aerosols and cirrus clouds, respectively (see Figure 4c,d). Figure 3: Height-time of total backscatter coefficients (**a**,**b**), extinction coefficient vs. altitude (**c**) and time evolution of cloud optical depth (COD) (**d**) for 10 April 2019. The capabilities of the CALIPSO to measure clouds with an unprecedented vertical and horizontal resolution, especially high cloud, is an advantage for the characterization of cirrus clouds and the validation of ground-based lidar systems. The validation of the ground-based lidar largely depends on the availability of a CALIPSO closest overpass to the station of interest and also the days of the operation of the lidar. In this study, the closet CALIPSO overpass was only available on 11 April 2019. Figure 5a shows the total attenuated backscatter data at 532 nm for a section of CALIPSO's orbit on 11 April 2019. The CALIPSO cloud classification, as well as the vertical profile of the extinction coefficient as the satellite passes the closest to the UZ lidar locations, are shown in Figures 5b and 5c, respectively. The cloud type that is represented by a white color is a cirrus cloud. The orbit tract of CALIPSO is shown in Figure 5d. It is evident in Figure 5a that there is an enhancement of the total attenuated backscatter (<0.003 km\({}^{-1}\)sr\({}^{-1}\)) at the height region between 9 and 13 km. This strong peak was classified as a cirrus cloud (see Figure 5b). During this time, the CALIPSO satellite also reported a significant enhancement of the extinction coefficient vertical profile, which is directly associated with a cirrus cloud (see Figure 5c). This independent observation by the CALIPSO satellite agrees with the observation presented in Figure 4. The CALIPSO satellite observations also reported an ice and water content of about 0.009 gm\({}^{3}\) at around 10 km height. The cirrus cloud events observed on both 10 and 11 April 2019 are very interesting because their COD is well above 1.0, thus indicating that the study area was dominated by dense cirrus clouds during this period. The optical depth of clouds is a crucial parameter concerning the radiation and scattering process of the cloud, and dense cirrus clouds events are less dominant in the atmosphere (e.g., [PERSON] et al. [2]). The variation of COD mainly depends on the thickness of the cloud [10] and density N of particles, and the mean particle size. In their study of cirrus clouds at two locations in the mid-latitudes of the southern (SH) and northern hemisphere (NH), [PERSON] and [PERSON] [26] reported a frequent detection of haze layers of cirrus cloud in the NH and highly depolarizing cirrus cloud only in the SH. The average thickness of \(\sim\)1.5 km of a cirrus cloud detected over a study area is within the range of what was reported by other authors such as [PERSON] and [PERSON] [10]. Figure 4: Height-time of total backscatter coefficients (**a**), time evolution of cloud optical depth (COD) (**b**), and extinction coefficient vs. altitude (**c**,**d**) for 11 April 2019.