http://www.staff.science.uu.nl/~delde102/Thunderst.Predictors.pdf

Thunderstorm predictors and their forecast skill for the Netherlands

Daily precipitation patterns over Switzerland are investigated by rotated and unrotated principal component analysis for the periods 1901–1990 (with 113 continuously operating rain-gauge sites) and 1961–1990 (with 304 sites). Empirical orthogonal functions are utilized to homogenize the precipitation series and to optimally transform the 113 series of the long-term record into a few variables. Several statistically significant linear trends are detected. This includes, in particular, a wintertime increase in precipitation by up to 30 per cent per 100 years in the western and northern parts of Switzerland. This trend is statistically significant at the 90 per cent level. In most parts of southeastern Switzerland, winter precipitation increased as well but by a smaller rate and at a slightly lower statistical significance level. For the period 1961–1990, precipitation amounts increased in most subregions and all seasons with the exception of summer.



A statistical model is formulated in order to isolate the contributions to the observed precipitation trends that are related to changes in either the frequency or the precipitation activity of Alpine weather classes. It is demonstrated that the observed precipitation trends cannot be interpreted based upon changing frequencies of weather classes (the observed changes would in fact lead to drier wintertime conditions), but are rather dominated by the tendency of most rain-producing weather types to produce more rain. Some physical mechanisms that could account for this unexpected result are also discussed. © 1997 by the Royal Meteorological Society.



Int. J. Climatol., 17: 1333–1356 (1997)



(No. of Figs: 9. No. of Tables: 5. No. of References: 69)

A principal component and long‐term trend analysis of daily precipitation in Switzerland

First airborne NOx (NO+NO2) measurements in anvils of active thunderstorms in Europe were performed in summer 1996 over southern Germany and Switzerland (47°-49°N). This field experiment LINOX (lightning-produced NOx) was designed to study the production of NOx by lightning discharges and the transport in convective storms. With the research aircraft Falcon of the Deutsches Zentrum fur Luft- und Raumfahrt, about 20 anvil penetrations were performed including measurements of NO, NO2, CO2, O3, and meteorological parameters. In thunderstorm anvils, mean NOx mixing ratios between 0.8 and 2.2 ppbv were measured with peak values reaching up to 4 ppbv. A considerable part of these enhancements could be attributed to the transport of polluted air from the planetary boundary layer (PBL) using CO2 as tracer for PBL air. NOx produced by lightning can be obtained by subtracting the fraction of NOx transported from the PBL from total NOx measured in the anvil. The NOx/CO2 correlation in larger cumulus clouds without lightning was used as reference for the transport of PBL air in the anvils. In smaller LINOX thunderstorms the contribution from lightning, respectively, PBL transport to anvil NOx, was about equal. However, in medium and large LINOX thunderstorms the contribution from lightning dominated (60–75%). For these kind of thunderstorms it was estimated that ∼1.0±0.5 ppbv NOx resulted from lightning production. The observations were used to quantify the NOx production per thunderstorm and to give a rough estimate of the annual production of NOx. For the global lightning nitrogen budget the uncertainties were considerable (0.3–22 Tg(N) yr−1). The mean value for the global NOx production rate by lightning in the upper troposphere was estimated to 4 Tg(N) yr−1.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JD02353

Transport and production of NO X in electrified thunderstorms: Survey of previous studies and new observations at midlatitudes

. The preconvective environment on days with ordinary, widespread, and severe thunderstorms in Southwest Germany was investigated. Various thermodynamic and kinetic parameters calculated from radiosoundings at 12:00 UTC were verified against subsequent thunderstorm observations derived from SYNOP station data, radar data, and damage reports of a building insurance company. The skill of the convective parameters and indices to predict thunderstorms was evaluated by means of probability distribution functions, probabilities of thunderstorms according to an index threshold, and skill scores like the Heidke Skill Score (HSS) that are based on categorical verification. For the ordinary decision as to whether a thunderstorm day was expected or not, the best results were obtained with the original Lifted Index (80% prediction probability for LI≤−1.73; HSS=0.57 for LI≤1.76), the Showalter Index, and the modified K-Index. Considering days with isolated compared to widespread thunderstorms, the best performance is reached by the Deep Convective Index. For days with severe thunderstorms that caused damage due to hail, local storms or floods, the best prediction skill is found again for the Lifted Index and the Deep Convective Index, but also for the Potential Instability Index, the Delta-θe Index, and a version of the CAPE, where the lifting profile is determined by averaging over the lowest 100 hPa.

/pdf/the-skill-of-convective-parameters-and-indices-to-predict-s2z2p9da72.pdf

The skill of convective parameters and indices to predict isolated and severe thunderstorms

In the context of climate change, it is of particular interest whether extreme events connected to severe thunderstorms have been increasing in number or intensity over the past few decades. Due to their small horizontal extent, such events are not entirely and uniquely captured by current observation systems. To obtain comprehensive information about the convective activity in the state of Baden-Wurttemberg (southwest Germany), we analysed different datasets for the period 1974–2003. They comprise thunderstorm days detected at synoptic stations, hail damage data from a building insurance company, large-scale circulation and weather patterns, and convective indices derived from radiosonde observations at 12:00 UTC.

While the annual number of thunderstorm days remained almost unchanged in the mean, hail damage and hail days significantly increased in the last three decades. Both damage and additional radar data indicate that the majority of hail days can be attributed to three specific circulation patterns. Two of the three patterns associated with the preferable occurrence of hail show a significant increase.

Most of the commonly used convective indices that depend upon surface temperature and moisture reveal a positive trend regarding both the annual extreme values and the number of days above/below specific thresholds. A relationship was established between the indices and the annual number of hail damage days, yielding correlation coefficients between 0.65 and 0.80. In contrast to this, indices derived from temperature and moisture at higher levels exhibit either a negative or no significant trend. It is shown that the trend directions of the indices may be attributed to differential temperature and moisture stratification in the various atmospheric layers. The significant positive trends of both surface temperature and water vapour can be concisely expressed by an increase in wet-bulb potential temperature. This indicates the presence of warmer parcels throughout the whole troposphere during convection. Copyright © 2009 Royal Meteorological Society

/pdf/recent-trends-of-thunderstorm-and-hailstorm-frequency-and-1qed4l37ih.pdf

Recent trends of thunderstorm and hailstorm frequency and their relation to atmospheric characteristics in southwest Germany

The preconvective environment on thunderstorm days in Switzerland north of the Alps has been investigated during a 5-yr period (1985–89). Thermodynamic and kinematic parameters calculated from the radiosounding in Payerne (started at 0000 and 1200 UTC) were used to characterize the initiation of convection. The best parameters were evaluated by using three methods: 1) skill scores, 2) probability distributions, and 3) mean temperature soundings and hodographs. For the decision whether a thunderstorm day was expected or not, the best results were obtained at 0000 UTC with the original Showalter index and at 1200 UTC with the SWEAT index. In addition, to decide whether an isolated or widespread thunderstorm day was expected, the most successful parameter was the modified CAPECCL. Furthermore, the best thermodynamic and kinematic parameters were combined to create new thunderstorm indices, similar to the calculations of the SWEAT index in the United States. The new thunderstorm indices especially de...

H. Huntrieser

Papers

Comparison of Traditional and Newly Developed Thunderstorm Indices for Switzerland

A New Thunderstorm Index for Switzerland