A. C. A. P. van Lammeren

Cloud effective particle size and water content profile retrievals using combined lidar and radar observations: 1. Theory and examples

In this paper, a novel lidar/radar method for simultaneously determining cloud particle effective size profiles (for water and ice clouds) and the lidar attenuation profile is described. Simulations and application to real data show that this procedure can be quite robust even in cases where significant lidar attenuation is present. In addition, the concept of a suitable lidar/radar effective particle size is introduced, and the determination of water contents for both water and ice clouds using this effective size together with the radar reflectivity profile is discussed. This paper concludes by presenting examples of effective size profiles and water content profiles inferred from measurements made during the Dutch Clouds and Radiation (CLARA) campaign. In a companion paper, it is demonstrated that the results of the inversion procedure compare favorably with infrared radiometer measurements as well as with in-situ measurement results.

Cloud remote sensing by combining synergetic sensor information

Abstract The accurate determination of the cloud liquid water (LWC) profile from one single remote sensing instrument is not possible. We present a technique, which allows the merging of measurements from different instruments. Additionally, the method can take into account climatological (virtual) information of cloud microphysics. The method is applied to measurements from a cloud radar and a 2-channel passive microwave radiometer. With the EU-project CLIWA-NET, which aims at the determination of highly accurate fields of the liquid water path (LWP) from a combination of ground-based stations and satellite measurements, more detailed input will be available for our method. Example measurements from a Pre-CLIWA-NET campaign are presented to demonstrate the potential of the upcoming CLIWA-NET campaigns, which will lead to long-term statistics of the LWC profile.

Combined lidar and radar cloud particle effective size retrievals made during CLARA

Abstract In principle, combined lidar and radar cloud soundings are capable of providing detailed height resolved information of the effective sizes of cloud particles. However, one of the obstacles to successfully using lidar and radar measurements to this end is the fact that it is difficult to account for the effects of attenuation, particularly with respect to the lidar signal. In this paper, a novel method for simultaneously determining cloud particle effective size profiles together with the lidar attenuation profile is presented. Simulations and the application to real data shows that this procedure appears to be quite robust even in cases where significant lidar attenuation is present.

Radar and lidar observations of the melting process in the bright band

The melting layer of precipitation is known for its high radar reflectivity, and is thus called the bright band. New and unexplained are lidar measurements of the melting layer. This optical instrument receives fewer reflections from the melting layer than from either the ice precipitation above or the rain below. To this phenomenon has been coined the name dark band by Sassen and Chen who published the first clear measurement of this phenomenon. In this article measurements are analysed using lidar together with radar to gain more insight into this dark band. The difference in lidar backscatter between melting layer and its environs is defined as its depth and can amount up to 20 dB compared to the rain (water dark band) and up to 30 dB compared to the ice above (ice dark band). The radar bright band is usually explained by an increase of the radio refractive index of the melting particle at the top of the melting layer and a decrease of particle size and number density (both due to collapse of the melting particle) at the bottom of the melting layer. Aggregation (in the top) and breakup (bottom) work together to increase the particle size in the middle of the melting layer. This enhances the radar reflectivity of the melting layer. There is still a debate on when this is significant. Explanations for the dark band that are discussed are: crystal imperfections, enhanced backscatter of raindrops for vertically pointing lidar, particle aggregation and breakup, collapse of the particle, and enhanced vertical backscatter of the ice precipitation.

Assessment report on NRP subtheme “Atmospheric processes & UV-B radiation”

Abstract The atmosphere is a very complex, open, dynamic and multi-causal relation system in which non-linear processes and feedback mechanisms play an important role. Research within this subtheme in NRP-1 focused on uncertainties in our understanding of three issues i.o. o − the role of clouds and aerosols on the radiation budget − the role of atmospheric ozone in global change and the effect of atmospheric change on UV-B climatology − trophospheric budgets of non CO2 greenhouse gases These issues are being dealt with in 12 projects. On average good progress has been made in many of the projects and through there are some weaknesses, the overall quality of science and technological developments is good and in some cases even excellent in comparison to international standards. Links with international programmes such as IGBP, CEC, EUREKA/EUROTRAC are well established.

Clouds-Radiation-Hydrologic interactions in a limited-area model

Abstract In this project work has been directed towards the improvement of the knowledge on clouds and the way they influence our climate. The activities include measurement of cloud properties on a regional scale (120×120 km 2 ), analysis of global satellite datasets and the development of a model environment to enhance the regional data analysis and the improvement of parametrization of clouds and radiation.