G band atmospheric radars: New frontiers in cloud physics

Clouds and associated precipitation are the largest source of uncertainty in current weather and future climate simulations. Observations of the microphysical, dynamical and radiative processes that act at cloud scales are needed to improve our understanding of clouds. The rapid expansion of ground-based super-sites and the availability of continuous profiling and scanning multi-frequency radar observations at 35 and 94 GHz have significantly improved our ability to probe the internal structure of clouds in high temporal-spatial resolution, and to retrieve quantitative cloud and precipitation properties. However, there are still gaps in our ability to probe clouds due to large uncertainties in the retrievals. The present work discusses the potential of G band (frequency between 110 and 300 GHz) Doppler radars in combination with lower frequencies to further improve the retrievals of microphysical properties. Our results show that, thanks to a larger dynamic range in dual-wavelength reflectivity, dual-wavelength attenuation and dual-wavelength Doppler velocity (with respect to a Rayleigh reference), the inclusion of frequencies in the G band can significantly improve current profiling capabilities in three key areas: boundary layer clouds, cirrus and mid-level ice clouds, and precipitating snow. © 2014 Author(s)

Assessment of small-scale integrated water vapour variability during HOPE

The spatio-temporal variability of integrated water vapour (IWV) on small scales of less than 10 km and hours is assessed with data from the 2 months of the High Definition Clouds and Precipitation for advancing Climate Prediction (HD(CP)2) Observational Prototype Experiment (HOPE). The statistical intercomparison of the unique set of observations during HOPE (microwave radiometer (MWR), Global Positioning System (GPS), sun photometer, radiosondes, Raman lidar, infrared and near-infrared Moderate Resolution Imaging Spectroradiometer (MODIS) on the satellites Aqua and Terra) measuring close together reveals a good agreement in terms of random differences (standard deviation 1 kgm2) and correlation coefficient (0:98). The exception is MODIS, which appears to suffer from insufficient cloud filtering. For a case study during HOPE featuring a typical boundary layer development, the IWV variability in time and space on scales of less than 10 km and less than 1 h is investigated in detail. For this purpose, the measurements are complemented by simulations with the novel ICOsahedral Nonhydrostatic modelling framework (ICON), which for this study has a horizontal resolution of 156 m. These runs show that differences in space of 3–4 km or time of 10–15 min induce IWV variabilities on the order of 0.4 kgm2. This model finding is confirmed by observed time series from two MWRs approximately 3 km apart with a comparable temporal resolution of a few seconds. Standard deviations of IWV derived from MWR measurements reveal a high variability (> 1 kgm2) even at very short time scales of a few minutes. These cannot be captured by the temporally lower-resolved instruments and by operational numerical weather prediction models such as COSMO-DE (an application of the Consortium for Small-scale Modelling covering Germany) of Deutscher Wetterdienst, which is included in the comparison. However, for time scales larger than 1 h, a sampling resolution of 15 min is sufficient to capture the mean standard deviation of IWV. The present study shows that instrument sampling plays a major role when climatological information, in particular the mean diurnal cycle of IWV, is determined

Use of remote sensing techniques and navigation data for tropospheric channel assessment

The objective of this contribution is the review of remote sensing and navigation data in order to provide an overview on meteorological parameters important for propagation modelling up to W band. Such data are also useful to assess the accuracy of the propagation models and analyse propagation impairment mitigation techniques (PIMTs). The review will focus on water vapour and cloud properties that can be deduced from observation in various parts of the electromagnetic spectrum. Both ground measurements and satellite observations are considered which offer various possibilities to capture the spatial distribution of these parameters. For clouds the importance of microphysical properties, e.g., liquid water path and effective radius, is highlighted as they control the signal transfer. Several example of ongoing satellite missions are given. © 2011 EurAAP

GEPROG - Genetisches Programmieren fuer Modellierung und Regelung dynamischer Systeme Schlussbericht

Available from TIB Hannover: F02B711+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

The added value of large-eddy and storm-resolving models for simulating clouds and precipitation

This study investigates, if atmospheric models with horizontal resolutions of 100 m to 2 km are able to better simulate key features, like clouds and precipitation, of the climate system than currently used models employing much coarser resolution and parameterized convection. Precipitation characteristics are much more realistic in the simulations with explicitly convection, already at kilometer resolutions. Increasing resolution to hectometer scales improves the simulation of precipitation only modestly, but substantially improves the simulation of clouds. The results suggest that new climate models, which explicitly resolve convection and the interaction with its environment, offer exciting opportunities to learn about the climate system