A Re-Evaluation of the Swiss Hail Suppression Experiment Using Permutation Techniques Shows Enhancement of Hail Energies When Seeding

Grossversuch IV is a large and well documented experiment on hail suppression by silver iodide seeding. The original 1986 evaluation remained vague, although indicating a tendency to increase hail when seeding. The strategy to deal with distributions of hail energy far from normal was not optimal. The present re-evaluation sticks to the question asked and avoids both misleading transformations and unsatisfactory meteorological predictors. The raw data show an increase by about a factor of 3 for the hail energy when seeding. This is the opposite of what seeding is supposed to do. The probability to obtain such a result by chance is below 1%, calculated by permutation and bootstrap techniques applied on the raw data. Confidence intervals were approximated by bootstrapping as well as by a new method called “correlation imposed permutation” (CIP).

A Re-Evaluation of the Swiss Hail Suppression Experiment using Permutation Techniques shows Enhancement of Hail Energies when Seeding

Grossversuch IV is a large and well documented experiment on hail suppression by silver iodide seeding. The original 1986 evaluation remained vague, although indicating a tendency to increase hail when seeding. The strategy to deal with distributions of hail energy far from normal was not optimal. The present re-evaluation sticks to the question asked and avoids both misleading transformations and unsatisfactory meteorological predictors. The raw data show an increase by about a factor of 3 for the hail energy when seeding. This is the opposite of what seeding is supposed to do. The probability to obtain such a result by chance is below 1%, calculated by permutation and bootstrap techniques applied on the raw data. Confidence intervals were approximated by bootstrapping as well as by a new method called "correlation imposed permutation" (CIP).

GNSS storm nowcasting demonstrator for Bulgaria

<p>GNSS is an established atmospheric monitoring technique delivering water vapour data in near-real time with latency 90 minutes for operational Numerical Weather Prediction in Europe within the EGVAP service. However, nowadays with advancement of GNSS processing the quality of real-time GNSS tropospheric products is well comparable to near-real time solution and in addition they can be provided in a temporal resolution of 5 minutes and low latency, suitable for severe weather nowcasting. The aim of the project is to exploit the added value of GNSS tropospheric product for nowcasting of convective storm by building demonstrators in support of public weather and hail suppression services in Bulgaria. In Bulgaria  thunderstorms and hail events are  occur between May and September with a peak in July. The convective Storm Demonstrator (Storm Demo) is based on GNSS tropospheric products and Instability Indices to derive site specific threshold values integrated and updated in real-time on a publicly accessible geoportal. The demonstrator targets development of service centered at GNSS products for two regions with hail suppression operations namely Northwestern and Central Bulgaria.<span>  </span>As a part of the Storm Demo real-time PPP processing will be conducted with G-Nut software for the first time in Southeast Europe for the hail suppression season May-September 2021. Evaluation of the real-time products will be performed using reprocessed GNSS tropospheric products.<span>  </span>The added value of the high temporal resolution of the GNSS tropospheric products will be investigated for selected storm cases.<span>  </span>This service will be unique in Europe and will serve as a prototype for real-time provision of GNSS products for storm nowcasting.<span> </span></p>

Environmental effects of silver iodide emitted by hail suppression systems in Aragón (Spain)

<p>Weather modification by means of cloud seeding techniques is widely implemented across the world. In areas where hail suppression systems are installed, silver iodide (AgI) particles are used.</p><p>Silver particles fall back to the surface thank to atmospheric deposition. In this research we follow a holistic approach to analyse silver accumulation in water, soils and sediments of Aragón (North-East Spain), where AgI emissions have been released for the last fifty years. We have also assessed silver bioaccumulation in plants and biota, and we have tested its effects in plant growth.</p><p>Our results show that silver concentrations in water and soils of areas covered by hail suppression networks are higher than in further areas, although concentrations are below legal thresholds. We have also observed that silver seems to be absorbed by plants and biota, which would act as a silver outflow and it may help to remove silver from the ecosystems.</p><p><strong>Acknowledgements</strong></p><p>This work was funded by Spanish State Research Agency and FEDER Funds via AgroSOS project (PID2019-108057RB-I00) and DONAIRE project (CGL2015-68993-R), and thanks to a pre-doctoral grant awarded by the Government of Aragon to J. M. Orellana-Macías (BOA 20/ 07/2017).</p>