Fernando de Pablo

Relationship between Convective Precipitation and Cloud-to-Ground Lightning in the Iberian Peninsula

Abstract The relationship between cloud-to-ground (CG) lightning and convective precipitation over the Iberian Peninsula during the warm season was analyzed. The database covered the period between 1992 and 1994 and the precipitation data from 68 meteorological observatories were used. Temporal and spatial scales of 1 month and 102 km2 were considered. Values of rain yield (defined as the ratio of convective precipitation to CG flash count over a common area) were centered around a mean value of ∼108 kilograms per flash (kg fl−1) but varied as a function of the climate regime, increasing from a mean value of 1.2 × 108 kg fl−1 for the semiarid region of the Iberian Peninsula to a mean value of 2.1 × 108 kg fl−1 for the humid region of the Iberian Peninsula. The correlation coefficients between convective precipitation and the CG flash count also varied with the climate regime. The correlation coefficient was higher for the semiarid zone (0.75) than for the humid one (0.65). These variations are physically ...

Effect of small urban areas in central Spain on the enhancement of cloud-to-ground lightning activity

Abstract Cloud-to-ground (CG) flashes in and around nine small towns of Spain were analysed using data of three years. CG-lightning activity was enhanced within and downwind (east) of most of these urban areas. The increase in lightning was examined in relation to population, urban size, PM10 and SO 2 concentrations. The results show that larger population and higher SO 2 concentration contribute to the increase in the number of CG-flashes. Urban size and PM10 concentration did not seem to be related to the enhancement in CG-lightning activity. In five of the nine towns examined, the enhancement in CG-lightning was most pronounced during 1200–2100 local time.

Cloud‐to‐ground lightning activity in the Iberian Peninsula: 1992–1994

For the first time, the temporal and spatial distribution of cloud-to-ground lightning activity in the Iberian Peninsula are being studied. The database covers the years 1992-1994, and it was recorded over 2.2 x 10 cloud-to-ground lightning flashes. The monthly variation shows a single peak in the warmer months (May to September) with a strong year-to-year variability. The diurnal cycle of lightning activity peaks at 1700 LT with a subsequent slow decrease toward the minimum in the morning hours. The percentage of positive flashes is 8%, although this percentage is higher in the winter than in the summer. The lightning flash polarity is found to be very similar throughout the day. The average multiplicity is found to be 2.0 for the negative flashes and 1. 1 for the positive flashes and is very similar in the winter and summer seasons, while the percentage of single-stroke flashes tends to increase in the winter. The median (mean) intensity is found to be 22.5 kA (32.4 kA) for the negative flashes and 52.3 kA (69.3 kA) for the positive flashes. The excessively high intensity for the positive flashes could be due to the detection system has low efficiency in detectiong weak amplitude flashes. The distribution of amplitudes is very similar in the winter and summer seasons. The decay at large amplitudes is slower for the positive flashes. The median and mean amplitudes are higher in the winter for both polarities. The spatial cloud-to-ground lightning distribution confirms the well-known preference for certain areas in the development of thunderstorms. The average maximum negative, positive, and combined flash densities are 3.1, 0.2, and 3.3 flashes km -2 yr -1 , respectively. The comparison between individual years shows a considerable year-to-year variability. The average percentage of positive flashes ranges from 0% to 41%. The grid block median peak current amplitudes vary from 12.5 to 47.4 kA for the negative flashes and from 17.6 to 107.5 kA for the positive flashes. The results are discussed in the context of other measurements taken at different parts of the world.

Relationship between cloud-to-ground lightning flashes over the Iberian Peninsula and sea surface temperature

The correlation between cloud-to-ground (CG) lightning anomalies over the Iberian peninsula and sea surface temperature (SST) anomalies in its bordering seas has been calculated. The results disclosed a significant link between them. The warmer SSTs in the Atlantic north-west of the Iberian Peninsula and in the Cantabrian Sea are related to increased CG lightning activity over the Iberian Peninsula. The warmer SSTs in the Atlantic south of the Iberian Peninsula are related to increased CG lightning over the northern half of the Iberian Peninsula and to decreased CG lightning over the southern half. The Mediterranean Sea does not show significant links with CG lightning. The way these links work seems to involve changes in the advection of moisture from the Atlantic Ocean and the Cantabrian Sea as well as changes in static instability. It was also observed that there is no significant link between CG lightning anomalies and land surface temperature anomalies over the Iberian Peninsula. Copyright

Analysis of convective precipitation in the western Mediterranean Sea through the use of cloud-to-ground lightning

The monthly convective precipitation (CP) and convective precipitation rate (CPR) over the western Mediterranean Sea are estimated using cloud-to-ground lightning flashes for the June to October period using data of 3 years (1992–1994). Rain yield was computed using the precipitation data from seven observing stations (all equipped with rain gauges) located on the Mediterranean coast of the Iberian Peninsula and in the Balearic Islands. The values obtained were 0.93×108 kg/fl for the negative flashes and 20.63×108 kg/fl for the positive flashes. Convective precipitation over sea was estimated from the rain yield using the cloud-to-ground (CG) lightning activity detected by a lightning detection network. Because no measured data on precipitation over sea are available, the estimated convective precipitation was compared with the monthly diagnostic surface convective precipitation data from the NOAA NCEP/NCAR climate data assimilation system. Analysis of the results revealed that convective precipitation over the western Mediterranean Sea is maximum in the months September and October and near the northeastern coast of the Iberian Peninsula (maximum in the order of 240 mm/month). The convective precipitation rate exhibits less time variability than convective precipitation, although its spatial distribution is similar.

Winter Lightning and North Atlantic Oscillation

Abstract The relationship between the North Atlantic Oscillation (NAO) and total (in cloud and cloud to ground) lightning activity during the wintertime (December to March) is analyzed. Lightning data from the Optical Transient Detector were used and were studied in the North Atlantic and western European area. The southern half of the area analyzed (latitudes lower than ∼50°N) was observed to have an increased (decreased) lightning flash rate associated with negative (positive) NAO index values. The opposite relationship was found when the northern half (latitudes higher than ∼50°N) was considered. In both cases, the effect of the NAO on the lightning activity was stronger over the eastern area analyzed. Low (clearly <1) absolute values of the NAO index seem to be associated with minimum lightning activity.