J. Handwerker

Cell tracking with TRACE3D—a new algorithm

Abstract An automated algorithm called TRACE3D is presented which identifies convective cells and tracks them in time and space by exclusively using radar reflectivity data as input. Identification of cells is performed by assembling contiguous regions that excel certain reflectivity thresholds. Tracking is done in that the position of a cell in a new radar image is predicted by an extrapolation procedure based on its former position; special care is taken in case of possible splitting and merging events. In comparing the results of the tracking algorithm with those from four test persons, TRACE3D shows a promising performance, and hence, it seems possible to apply this algorithm as a nowcasting tool.

KITcube - a mobile observation platform for convection studies deployed during HyMeX

With the increase of spatial resolution of weather forecast models to order O(1 km), the need for adequate observations for model validation becomes evident. Therefore, we designed and constructed the ‘‘KITcube’’, a mobile observation platform for convection studies of processes on the meso-c scale. The KITcube consists of in-situ and remote sensing systems which allow measuring the energy balance components of the Earth’s surface at different sites; the mean atmospheric conditions by radiosondes, GPS station, and a microwave radiometer; the turbulent characteristics by a sodar and wind lidars; and cloud and precipitation properties by use of a cloud radar, a micro rain radar, disdrometers, rain gauges, and an X-band rain radar. The KITcube was deployed fully for the first time on the French island of Corsica during the HyMeX (Hydrological cycle in the Mediterranean eXperiment) field campaign in 2012. In this article, the components of KITcube and its implementation on the island are described. Moreover, results from one of the HyMeX intensive observation periods are presented to show the capabilities of KITcube.

Observations of Kinematics and Thermodynamic Structure Surrounding a Convective Storm Cluster over a Low Mountain Range

Abstract Measurements of a convective storm cluster in the northern Black Forest in southwest Germany have revealed the development of a warm and dry downdraft under its anvil cloud that had an inhibiting effect on the subsequent development of convection. These measurements were made on 12 July 2006 as part of the field campaign Prediction, Identification and Tracking of Convective Cells (PRINCE) during which a number of new measurement strategies were deployed. These included the collocation of a rotational Raman lidar and a Doppler lidar on the summit of the highest mountain in the region (1164 m MSL) as well as the deployment of teams carrying radiosondes to be released in the vicinity of convective storms. In addition, an aircraft equipped with sensors for meteorological variables and dropsondes was in operation and determined that the downdraft air was approximately 1.5 K warmer, 4 g kg−1 drier, and therefore 3 g m−3 less dense than the air at the same altitude in the storm’s surroundings. The Raman...

Dry and moist convection in the boundary layer over the Black Forest - a combined analysis of in situ and remote sensing data

During the COPS experiment performed in south-western Germany and eastern France in 2007, several insitu and remote sensing systems were operated at Hornisgrinde - the highest summit of the northern Black Forest mountains. For this case study, data from a surface flux station, radiosondes, cloud camera, cloud radar, wind lidar, water vapour differential absorption lidar, and microwave profiler were used to investigate turbulence characteristics in cloud-free and cloud-topped convective boundary layers (CBLs). Short time intervals were analysed, during which dry and moist convective cells occurred, in order to obtain insight of the processes that determine the turbulent characteristic in the CBL. The frequently-used aerosol concentration was used to calculate the CBL height, zi. It was found that active CBL clouds penetrated deeper into the free troposphere than dry convective cells. In the cloud-free CBL the normalised variance of the vertical velocity, rw 2 , decreased to zero approximately at zi, while rw 2 was nearly constant between 0.5 and 1 z/zi in the cloud-topped CBL. The higher normalised rw 2 values in the cloud layer could be attributed to the additional elevated heat source due to condensation. In the cloud-free CBL the latent heat flux showed a strong decrease between 0.7 and 1.1 z/zi, i.e., it considerably moistened the upper part of the CBL and entrainment zone. In the cloud-topped CBL the latent heat flux decreased significantly above the CBL top only and became zero at about 1.4 z/zi. CBL height calculations, which took measures of the turbulence into account, resulted in normalised rw 2 and E profiles, which became zero at the CBL top and appeared more appropriate for CBL height scaling over complex terrain. The case studies demonstrated that only the combined use of different monitoring systems allowed for the recording of the entire structure of the convective cells and that synergetic measurements in cloud-topped CBLs were indispensable to capture the latters’ turbulent characteristics. Also, significant differences between turbulent characteristics in cloud-free and cloud-topped CBLs became evident.

Optimal Determination of Parameters for Gamma-Type Drop Size Distributions Based on Moments

AbstractMeasured raindrop size distributions are often approximated by analytical functions. The parameters determining such functions are usually derived from measured data. This procedure can suffer from various uncertainties. The most important of which are (i) the limited detection range of measuring devices such as, for example, disdrometers, and (ii) poor statistics resulting from the rare appearance of relatively large drops.One way to derive the parameters is the moments method that has a degree of freedom in the choice of the moments. The aim of this study is to find an optimal choice of moments. To this end, numerical experiments are performed by calculating random samples from drop populations with gamma-shaped size distributions. These samples are evaluated as they were recorded by an ideal disdrometer whose single limitation is the cutoff with respect to very small and very large raindrops. From that data the parameters mentioned above are determined by the moments method. The truncation of t...

A Synergy Approach to Estimate Properties of Raindrop Size Distributions Using a Doppler Lidar and Cloud Radar

Abstract Remote sensing systems like radars and lidars are frequently used in atmospheric measurement campaigns. Because of their different wavelengths, they operate in different scattering regimes. Combined use may result in new measurement options. Here, an approach to estimate raindrop size distribution using vertical velocities measured by a lidar–radar combination is introduced and tested using a 2-μm Doppler lidar and a 35.5-GHz cloud radar. The lidar spectra are evaluated to deduce air motion from the aerosol peak and the fall velocity of the raindrops from the rain peak. The latter is weighted by the area (D2) of the scatters. The fall velocity derived from radar measurements is weighted by D6 (Rayleigh approximation). Assuming a size-dependent fall velocity and an analytical description of the drop size distribution, its parameters are calculated from these data. Comparison of the raindrop size distribution from the lidar–radar combination with in situ measurements on the ground yields satisfying...