ALBERT

Beschreibung: Results of field experiments and numerical simulations on the creation of artificial updrafts and clouds under UAEREP project APP-REP-2017-02120 are discussed. Tested method incorporated a vertically directed jet produced by aircraft turbojet engine and abundantly saturated with different types of hygroscopic aerosol for enhancing its buoyancy through water vapor condensation. 19 full-scale real atmosphere experiments were carried out in the UAE and following physical effects were obtained: 13 cases — formation of small translucent aerosol-droplet clouds in a cloudless sky; 3 cases — compaction and further formation of the enlightenment zone in clouds into which a jet saturated with hygroscopic aerosols was injected; 3 cases —radar echo spot appearance on the downwind side 10-20 min after the start of experiment; 2 cases — cyclonic swirling and convergence of small natural clouds (Cu Hum) in the direction of the jet; 1 case - scattering of a cumulus cloud passed over the jet. In at least 2 cases there was a short-term (about 30 seconds) falling of raindrops on the site by the end of the experiments. Formation of a precipitable Cb cloud was never noted. Therefore, the impacts were lower than expected. Under the conditions of low air humidity, typical for the UAE, and the slowness of the condensation process on the used hygroscopic aerosol, the replenishment of the jet energy by the heat of condensation is too small to support the jet buoyancy, and the power of the used jet engine is insufficient.

Beschreibung: With the projected expansion of arid/semi-arid regions in a warming world, precipitation enhancement activities such as cloud seeding will become increasingly popular and relied upon. Due to the inherent costs, a successful planning is crucial, which involves accurate model predictions. In this talk, the usefulness of the Weather Research and Forecasting (WRF) model forecasts for guidance into seeding operations in the United Arab Emirates, where seeding activities have been conducted for more than two decades, is assessed. The WRF predictions are compared with ground-based, satellite-derived and radar reflectivity data, and in-situ observations onboard the airplanes used to perform the seeding operations. WRF is found to have higher skill in simulating the observed cloud top pressure/temperature than the cloud fraction, with the model vertical velocity predictions also more skillful than those of the radar reflectivity. A stronger Arabian Heat Low in the model leads to drier conditions which, together with a surface cold bias, limits the spatial extent and vertical depth of the simulated convective clouds. Development of convective rolls in the boundary layer is reported in both observations and simulations and their interaction with cold pools from convective clouds promote the development of secondary convection. When considering the two factors needed for a successful seeding operation, the presence of an updraft and clouds, the model-predicted seeding regions largely match the areas where precipitation was observed. As the proposed WRF set up can be used operationally, the model forecasts will bring added value to the seeding activities in the country.