XXVIII OSTIV Congress

June 8 - 15, 2006

Eskilstuna, Sweden

Papers presented within the Meteorology Session

E. Hindman, S. Saleeby, O. Liechti, W. Cotton A system for planning soaring flights in northeastern Colorado USA
O. Liechti Verification of thermal forecasts with glider flight data
B. Olofsson Automatic Thermal Forecasts from the Swedish HIRLAM Model
B. Sigrist Use of topographic radar scans to identify thermal hotspots in Alpine areas
C. Lindemann Convergences Mammatus


Abstracts of the papers presented within the Meteorology Session

E. Hindman, S. Saleeby, O. Liechti, W. Cotton: A system for planning soaring flights in northeastern Colorado USA
Currently, USA glider pilots do not have an on-line, interactive system to plan flights like their European counterparts. In Europe, a glider pilot interacts with an atmospheric numerical model to determine the most feasible flight for a given day: essentially the pilot "flies" through the predicted weather to plan a flight. This interaction is accomplished through the TopTask algorithm nested in the on-line pilot briefing system called pc_met of the German Weather Service. As a first step in the USA, the Regional Atmospheric Modeling System (RAMS) at the Colorado State University has been coupled to the A & K TopTask Competition (TTC) algorithm. The coupling was accomplished following the Olofsson and Olsson lift-rate procedures. The RAMS-TTC system was tested using 35 Colorado Soaring Association On-line Contest flights. The flights occurred over 15 days in 2004 and 2005 from Owl Canyon Gliderport (OCGP), Wellington CO. On average, the RAMS-TTC system predicted a potential flight distance of 747 km while the actual flight distance was 289 km. The average predicted task speed was 119 kph while the average actual speed was 104 kph. The average thermal top was predicted to be 4600 m MSL while average achieved top was 4400 m MSL. These results demonstrate the significant soaring conditions in northeast Colorado. Closer predicted and actual task speeds are expected from the RAMS-TTC system using results from a competition, as has been shown for Viking Glide 2005 by Liechti using the TTC system in pc_met. Two competitions are planned for OCGP, one in April 2006 and the other in May 2006. RAMS-TTC results from these competitions will be presented at the Congress.

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O. Liechti: Verification of thermal forecasts with glider flight data
Post-processing of numerical weather prediction with a regional convection model provides the meteorological information that is crucial to soaring pilots: wind, lift rates, and climb altitude. Regional forecasts are presented by showing the potential flight distance for a standard class glider on a geographical map ? a very intuitive form for pilots. Based on the regionalized forecasts specific glider flight tasks can be planned and optimized by applying a software tool named TopTask. The tool allows to specify the best glide ratio and the corresponding glide speed of the glider to be used - be it a paraglider or an open class sailplane. This flight planning technique for gliding has been available for national and international gliding championships such as Swiss Glide 2004 and Viking Glide 2005. Task speeds obtained from to TopTask were compared to scored speeds for these competitions. Recorded flights were simulated with TopTask in order to compare the forecasted cloud base altitude to the flight altitude and the task speeds of the flights to the forecasts. Finally, flight plans based on different meteorological models like LME-TOPTHERM and HIRLAM were compared to the scored speeds. Results will be presented at the Congress. With the help of TopTask recorded flights can be used to tune the forecasting procedures for convective lift rates and for the depth of the convective boundary layer. Operational numerical thermal forecasts have reached a quality that is useful for soaring practice. Self-briefing systems make these forecasts available and provide the possibility of meteorological flight planning to the gliding community.

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B. Olofsson: Automatic Thermal Forecasts from the Swedish HIRLAM Model
Thermal forecasts for glider pilots are produced automatically from the operational NWP model in Sweden. Some extra algorithms are used in the post-processing to calculate the thermal height and mean rate of climb from the forecast vertical profile in every gridpoint.

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B. Sigrist: Use of topographic radar scans to identify thermal hotspots in Alpine areas
Thermals are part of the atmospheric energy flow caused by solar irradiation. The question behind this project, called TherMap, has been whether variations of the solar irradiance, caused by the local topography, could be a valid predictor of thermals. Using digital elevation data the local irradiance was therefore computed for each mesh, date and time, and the results displayed on maps, leading to first plausible results for the morning hours of mountain areas. In a second step these models were refined to consider the thermal inertia of the soil and the air, the different vegetation factors, as well as the reflection of snow surfaces. For Alpine areas the resulting maps turned out to show a high level of coincidence with superimposed flighttracks. For topologically less differentiated regions, like the Jura, the results were mixed. No conclusive results could be obtained for topologically still smoother landscapes, where other factors are likely to be predominant.
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C. Lindemann: Convergences Mammatus
Cloudstreets have been observed by satellite quite often. Radiosoundings are evaluated for wind and temperature profiles for these occasions. A first conclusion is that cloud streets must form at a curved profile of Kuettners theory, but can form with increasing wind velocity with hight also. Secondly convergence lines over the central mountains of Spain are detected, which sometimes can extend into the plain. Another interesting phenomena "mammatus clouds" were observed and touched during a gliding flight over the Andes.

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