# First Observations of Cirrus Clouds Using the UZ Mie Lidar over uMhalthuze City, South Africa
## 1 Introduction  
Cirrus clouds are upper troposphere and lower stratosphere atmospheric clouds that have attracted much attention over the years due to their impact on the earth's radiation budget and thus climate [1, 2]. The microphysical and optical properties of cirrus clouds are known to cause a warming effect in the tropics and a cooling effect at mid-latitudes [2, 3]. Furthermore, cirrus clouds can be the platform for the genesis of heterogeneous reactions that influence the ozone budget in the lower stratosphere. In general, clouds in the atmosphere are composed of hydrometeors that differ in phase, size, and shape. Hydrometeors in the atmosphere are mainly water droplets, ice crystals, raindrops, graupel, hail, and snowflakes [4]. Depending on the vertical temperature profile, the different hydrometeors can be present in all clouds in a more or less distinct number concentration. Clouds cover more than two-thirds of the earth's surface and play a dominant role in the energy and water cycle of our planet [5, 6]. The net cloud radiative effect on the climate system depends on the amount, height, and optical depth of clouds. Low-level clouds tend to be relatively thick optically and are typically composed of spherical water droplets, and their overall impact is to cool the planet. On the other hand, high-level clouds are optically thin and are composed mostly of ice crystals, with a wide variety of shapes and sizes, and their overall impact is to warm the planet. Clouds are also an essential variable in the climate system because they are directly associated with precipitation through microphysical processes and with aerosol loading through the aerosol aqueous-phase chemistry and wet removal process [4]. Physically, cloud-radiation interactions depend largely on the cloud's macrophysical (e.g., cloud fraction, liquid and ice water path) and microphysical (e.g., cloud droplet number, size, and ice particle habit) properties. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) has been in orbit since 2006 and has been used to study the local and global spatialdistributions and heights of clouds. One of the advantages of CALIPSO is its capability to detect thin cirrus clouds. The high-quality vertical backscattering coefficients and depolarization ratio measurements are used to derive the vertical structure and properties of thin clouds [7]. Because of the sensitivity to very thin cirrus clouds, i.e., subvisible cirrus clouds with an optical depth of about 0.01, CALIPSO can provide information on multiple cloud layers. Furthermore, the light detection and ranging (lidar) instrument has also proven to be amongst the most effective instruments in studying and improving our understanding of cirrus clouds. One of the most important parameters is the lidar ratio (LR), i.e., extinction to backscattering ratio. LR depends on several characteristics of the particles, including their shape, size distribution, and refractive index [8]. Therefore, LR can provide indications about the ice-crystal characteristics [9]. Therefore, this makes lidars vital in studying cirrus clouds. Several authors [10,11] have used lidars to study cirrus clouds. More recently, the University of Zululand (UZ) (28.85\({}^{\circ}\) S, 31.84\({}^{\circ}\) E) installed and commissioned a Mie lidar system that is operated to measure clouds and aerosols. In contrast to other continents, the UZ lidar is one of the only two lidars that are available in Africa and, at present, is the only one operational. UZ is situated in the Empangeni/Richards Bay (uMhlathuze City), a city that is highly industrialized [12]. This study area is also situated at the center of the sugarcane fields of KwaZulu Natal Province of South Africa. The sugarcane fields are owned by both large commercial companies and partly owned by local communities. The area is also dominated by sugar mills.