![]() ![]() Pattern Classification for northwest airflowsĪ northwest airflow brings unstable and cool or even cold air from higher latitudes over the relative warm North Sea to the Netherlands. However some events seemed to be independent of this typical North Sea process. Significant cold-season convection was often triggered over the North Sea, combining cells to form larger cells over land. Most of the cases with winds more southwesterly than 250 degrees had thunderstorms with warm-season characteristics. ![]() 26% occurred with a wind from the SW quadrant, mainly between 250-270 degrees. 68% of the lightning encounters occurred with a 700hPa flow out of the NW (270 through 360 degrees) quadrant. About 44% of the cases contained tops of convective clouds at only 15,000 ft or less. The convective areas showed little change in intensity and coverage, with only 5% of the cases showing an overall decreasing trend and 25% of the cases showing an increasing trend. In some cases we were able to relate a single recorded lightning strike with the reported aircraft lightning incident. It was observed that lightning strikes invariably were recorded from cells with a minimum intensity of 31dBZ (in a range to over 47 dBZ) on the KNMI-radar. However, the soundings in nearly every case where EL and LCL criteria were met, showed a range of temperatures in the clouds between –100C and –200C where ice and supercooled liquid water droplets can co-exist, stimulating the separation of electrical charges during the convective process. ![]() In all cases, the temperatures observed at the Lifting Condensation Level (LCL) were above the –100C threshold criteria required for cloud-to-ground strike, but Equilibrium Level (EL) temperatures were generally not cold enough (below -200C) to reach the criteria of the Storm Prediction Center (SPC) of the US National Weather Service (NWS) for the prediction of cloud-to-ground lightning3). If only data is considered for wich radar echoes were observed, threshold values for potential convective activity were reached for all stability indices in over 80% of the cases. With the help of the radar data several cloud and precipitation characteristics that are used in aviation were derived and from the SAFIR/FLITS Lightning data the frequency of strikes and correlation with detected precipitation echoes were derived.Īs in the Fahey study (2), a strong correlation between stability indices from the nearest sounding observation and the KLM lightning encounters was noted. From the De Bilt soundings several instability indices were derived, as well as the 700hPa (Flight Level 100) wind direction and speed and temperature. In this highlight a summary of this lightning study for Amsterdam Airport is presented first, followed by an introduction of the so called awareness report for Aircraft Induced Lightning (AIL), a new tool to make users aware of the occurrence of this specific weather situation in the Amsterdam Flight Information Region (FIR), and some conclusions.įor the study we used archived radiosonde data (twice a day, station De Bilt), METAR data (Schiphol Airport), radar and lightning data (from the KNMI SAFIR/FLITS network) and 62 KLM Pilot Reports. For a better understanding an additional study was performed, based on the NWA study2) in the cold season (October 2003 - April 2007). KLM-studies (1998–2006) on lightning encounters in the Dutch Airspace show that 84% of all encounters occur in winter at low altitudes around 3000ft and only 16% in summer. KNMI has observed that lightning originating from 10.000 to 15.000 ft cloud-tops (3-5km) is not uncommon and aviation meteorologists have speculated that the aircraft in the vicinity frequently trigger the lightning strikes. Compared to other commercial airports like Frankfurt (5 days), Brussels and Hamburg (8), Rotterdam (9) and Paris (4) this is remarkably high. Located at about 12 km to the east of the North Sea, the climatology of Schiphol shows 13 days with thunderstorms in the cold season. Next, an examination was done of the weather conditions surrounding KLM aircraft during lightning encounters around Amsterdam Airport Schiphol for the ‘cold-season’ months. One result was the discovery that 40% of all lightning encounters with NWA aircraft occurred during the months of October through April, which is not the period of the most frequent thunderstorm activity during the ‘warm season’. The focus of the study was to look at cold season aircraft lightning encounters in relation to the characteristics of the surrounding atmosphere. At Northwest Airlines (NWA) a study (2) was done in 2006 with historic data from NWA aircraft lightning encounters from 1997 through early 2006. In this hightlight a study (1) on lightning encounters around Amsterdam Airport is summarized. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |