Special issue  

The "HD(CP)² Observational Prototype Experiment" (HOPE) has been designed to provide a unique view into clouds and their radiative aspects by combining state-of-the-art remote-sensing instrumentation. Such dense observations on process scale are necessary to capture the sub-grid variability of today's numerical weather prediction model and to assess microphysical properties that are subject to parameterizations even at high-resolution simulations. Specifically, HOPE observations will be used for a critical model evaluation HD(CP)² that will be run at 100m resolution over central Europe. The main goals of HOPE are to provide a most complete set of calibrated products of atmospheric parameters and to identify processes relevant for the formation of clouds and precipitation.

In order to achieve the dense instrumental coverage, the agricultural area around the atmospheric observatory JOYCE (Jülich Observatory for Cloud Evolution) in western Germany was chosen and complemented with two additional supersites and networks from April to May 2013. Three supersites formed a triangle with about 4km side length. The deployed instruments include Doppler lidars, Raman lidars (aerosol & cloud particles, water vapor, temperature), water vapor DIAL, ceilometers, microwave radiometers, cloud Doppler radars, sun photometers, different types of meteorological towers (up to 120m), a network pyranometer, sky imagers, as well as precipitation radar partly with polarization capabilities. This set of instruments forms the densest setup of remote-sensing and surface flux instruments to date.

Together with in total radiosonde launches (every 3h during intensive observation periods), the instruments captured the mean and turbulent thermodynamic state of the atmosphere and the vertically resolved and to some extent the 3-D resolved distribution of aerosol, cloud and precipitation particles as a function of time over a horizontal domain of 10 by 7km². Horizontal fields of standard meteorological parameter and surface fluxes of latent and sensible heat as well as solar and thermal radiation fluxes have been obtained. For the first time to our knowledge, a combination of scanning water vapor, temperature and Doppler lidar as well as coordinated scans with microwave radiometer and cloud radar were performed. Categories of meteorological events were identified, and data examples of these categories will be presented and discussed. It is demonstrated how the combination of active and passive, optical and microwave ground-based remote sensing yields also via desired redundancy a consistent picture of the atmospheric state and that through temporal changes of atmospheric and surface flux properties insights on lower atmospheric processes are revealed. The contributing manuscripts will briefly describe the set of instruments and the corresponding retrieved physical parameter with their spatial and temporal resolution followed by a synopsis of the meteorological conditions during the campaign. On the basis of characteristic intensive observation periods, case studies for clear skies, convective clouds, and precipitation will be presented and discussed. In a follow-up campaign in September 2013 in Melpitz, Germany, additional aerosol and cloud microphysics measurements on-board a helicopter-based platform were performed and will be reported as well.