ALBERT

Description: For decades, whistlers observed on the ground at mid and high latitudes have been used for diagnostics of Earth's plasmasphere. Whistlers have also been observed at low latitudes however, the propagation characteristics of low latitude whistlers are poorly understood thus they have not been used effectively as a diagnostic for the low latitude ionosphere. One key limitation with past studies has been lack of knowledge of the whistler source lightning location. Here we present the first cases of low latitude ground whistlers most likely linked with their causative lightning discharges in the conjugate zone. The Global Lightning Dataset 360 (GLD360) detected lightning discharges were found to be located close to the conjugate location of the recording stations, providing direct evidence of inter-hemispheric propagation at the low latitudes. A total of 864 whistlers were observed at Allahabad, India (Geomag. lat. 16.05°N; Geomag. long. 155.34°E; L = 1.08) during the night of 26 January 2011. Using GLD360 network data, we show the occurrence of thunderstorm activity between 200 and 450 km from the conjugate point of Allahabad. We also report the distribution of peak currents of whistler-producing lightning, which demonstrate a cutoff at 30 kA.

Description: Due to its low topographic relief, unique hydrology, and the large interannual variability of precipitation, Florida is especially vulnerable to climate change. In this paper, we investigate a comprehensive collection of climate metrics to study historical trends in both averages and extremes of precipitation and temperature in the state. The data investigated consists of long-term records (1892–2008) of precipitation and raw (unadjusted) temperature at 32 stations distributed throughout the state. To evaluate trends in climate metrics, we use Zhang et al .’s iterative pre-whitening method, which aims to separate positive autocorrelation from trend present in time series. Results show a general decrease in wet season precipitation, most evident for the month of May and possibly tied to a delayed onset of the wet season. In contrast, there seems to be an increase in the number of wet days during the dry season, especially during NDJ. We found that the number of dog days (above 26.7 °C) during the year and during the wet season has increased at many locations. For the post-1950 period, a widespread decrease in the daily temperature range (DTR) is observed mainly due to increased daily minimum temperature (Tmin). Although we did not attempt to formally attribute these trends to natural versus anthropogenic causes, we find that the urban heat island effect is at least partially responsible for the increase in Tmin and its corresponding decrease in DTR at urbanized stations compared to nearby rural stations. In the future, a formal trend attribution study should be conducted for the region. Copyright © 2011 John Wiley & Sons, Ltd.

Description: We have examined trends in temperature and precipitation parameters for the Arabian Peninsula (AP) during the last 2 to 3 decades. The data set has been carefully quality controlled and checked for homogeneity. Although of low density (21 stations) and relatively short time period, a clear picture of climate change in the region has emerged. The general pattern of the AP mean annual temperature trend is one of warming, with 14 of 21 stations show statistically significant warming at 0.05 level and most at 0.001 level and only one (Seeb) showing statistically significant cooling. The highest statistically significant mean annual warming trends are found in Oman (Sur = 1.03°C decade−1) and Emirates (Dubai = 0.81°C decade−1). The season of maximum warming in mean temperature is March to April. The highest monthly mean temperature trend in the AP occurs in Sur in May (1.47°C decade−1). There is a broad statistically significant increase in mean annual maximum temperature in AP in 12 out of 21 stations, with the highest trends in central and eastern/southeastern AP. Only SW AP and the Gulf of Oman do not show warming. The highest monthly maximum temperature trend in the AP occurs in Bahrain in March (2.27°C decade−1). The second highest significant warming trends are reported in Doha in February (1.54°C decade−1). For minimum temperature, 16 out of 21 stations show statistically significant warming trends, with the highest annual trends observed in the Emirates (Dubai = 1.24°C decade−1), northwest Oman (Sohar = 1.17°C decade−1) and Qatar (Doha = 1.13°C decade−1). The highest monthly minimum temperature warming rate occurred in October. Both Dubai and Kuwait reported the highest significant rate of 2.00°C decade−1. The general mean annual diurnal temperature range trend is negative in the AP, with six out of 21 stations show statistically significant negative trends while three stations show statistically significant positive trends. Trends in mean annual precipitation are significant at only two stations which show a decrease in precipitation.

Description: Structural analysis of the southern Tunisian Atlas was carried out using field observation, seismic interpretation, and cross section balancing. It shows a mix of thick-skinned and thin-skinned tectonics with lateral variations in regional structural geometry and amounts of shortening controlled by NW-SE oblique ramps and tear faults. It confirms the role of the Late Triassic–Early Jurassic rifting inheritance in the structuring of the active foreland fold and thrust belt of the southern Tunisian Atlas, in particular in the development of NW-SE oblique structures such as the Gafsa fault. The Late Triassic–Early Jurassic structural pattern is characterized by a family of first-order NW-SE trending normal faults dipping to the east and by second-order E-W trending normal faults limiting a complex system of grabens and horsts. These faults have been inverted during two contractional tectonic events. The first event occurred between the middle Turonian and the late Maastrichtian and can be correlated with the onset of the convergence between Africa and Eurasia. The second event corresponding to the principal shortening tectonic event in the southern Atlas started in the Serravalian-Tortonian and is still active. During the Neogene, the southern Atlas foreland fold and thrust belt propagated on the evaporitic décollement level infilling the Late Triassic–Early Jurassic rift. The major Eocene “Atlas event,” described in hinterland domains and in eastern Tunisia, did not deform significantly the southern Tunisian Atlas, which corresponded in this period to a backbulge broad depozone.

Description: ABSTRACT Triassic outcrops in the Atlassic zone of northern Tunisia may be modelled in two ways: salt bodies piercing through Cretaceous terrains or Triassic salt flows stratified within an Albian series. Both models find support from gravity data and are debatable. To evaluate the mass distribution changes with depth, the Bouguer anomaly of the El Kef-Ouargha region was successively decomposed into regional and residual components to construct multiple pseudo-depth slices and apparent density maps. Analyses of gravity lows clearly show a vertical continuity of less dense materials below the Triassic salt outcrops. These features can be explained by salt diapirism during Mesozoic and Cenozoic. Further, gravity data tend to indicate less dense materials below Aptian outcropping in Jebel Aite (Oued Bou Adila); thus suggesting Triassic materials occurring at depth. In addition, dense entities were recognized under Mio-Pliocene and Quaternary deposits, which are thought to correspond to Cretaceous paleoshoals currently collapsed by non-outcropping faults. Our findings lend support to a diapir model intruding overburden rather than the salt glacier model stratified in the Albian series proposed by some authors as the genetic structural model for Triassic material-bearing series in the north of Tunisia.

Description: ABSTRACT [1]  This paper adopts an efficient strategy that allocates the network resources to the users according to the transmission rate requirement. Based on cooperation and the use of variable length spreading codes, the terminals requiring high transmission rate are supported by larger bandwidth and power in order to enhance their quality of service. The proposed resource allocation strategy assigns the terminals with low transmission rate to cooperate with those with high transmission rate by dedicating a part of their bandwidth and power to either relay their data or send a part of it. This will result in a slight limitation on the performance of the cooperating terminals (low rate). Two proposed schemes are presented namely the Relaying strategy and Re-Allocation strategy. These strategies are evaluated against the commonly used Rate-Matching algorithm which constrains the terminals to fairly share the bandwidth regardless of the transmission rate. The proposed receiver is simple and efficient and the utilized spreading codes provide signal separation and limits multiple access interference MAI. In a CDMA based framework supporting multi-rate transmissions, a thorough performance assessment in terms of the error probability and the probability of outage is discussed for the considered strategies under different transmission conditions. The proposed strategies enhance the performance of the high rate user compared to the rate matching algorithm and slightly hold back the low rate user performance. Moreover, the re-allocation strategy enhances the system capability to support higher transmission rate at no additional cost.

Description: Due to its low topographic relief, unique hydrology, and the large interannual variability of precipitation, Florida is especially vulnerable to climate change. In this paper, we investigate a comprehensive collection of climate metrics to study historical trends in both averages and extremes of precipitation and temperature in the state. The data investigated consists of long-term records (1892–2008) of precipitation and raw (unadjusted) temperature at 32 stations distributed throughout the state. To evaluate trends in climate metrics, we use Zhang et al .’s iterative pre-whitening method, which aims to separate positive autocorrelation from trend present in time series. Results show a general decrease in wet season precipitation, most evident for the month of May and possibly tied to a delayed onset of the wet season. In contrast, there seems to be an increase in the number of wet days during the dry season, especially during NDJ. We found that the number of dog days (above 26.7 °C) during the year and during the wet season has increased at many locations. For the post-1950 period, a widespread decrease in the daily temperature range (DTR) is observed mainly due to increased daily minimum temperature (Tmin). Although we did not attempt to formally attribute these trends to natural versus anthropogenic causes, we find that the urban heat island effect is at least partially responsible for the increase in Tmin and its corresponding decrease in DTR at urbanized stations compared to nearby rural stations. In the future, a formal trend attribution study should be conducted for the region. Copyright © 2011 John Wiley & Sons, Ltd.

Description: We estimated the performance characteristics of the Global Lightning Dataset (GLD360) using rocket-and-wire triggered lightning data acquired at Camp Blanding, Florida in 2011–2013. The data set consisted of 201 return strokes and 84 kiloampere-scale (≥1 kA) superimposed pulses (initial continuous current pulses and M-components) in 43 flashes. All the events transported negative charge to ground. The GLD360 detected 75 strokes and 4 superimposed pulses in 29 flashes. The resultant detection efficiencies were 67% for flashes, 37% for strokes, and 4.8% for superimposed pulses. Out of 75 detected strokes, 1 (1.3%) was reported with incorrect polarity. The median location error was 2.0 km and the median absolute current estimation error was 27%. This is the first evaluation of GLD360 performance characteristics relative to absolute ground-truth, with all previous evaluations being relative to other locating systems. The results presented in this work may be applicable to regions in and around Florida.

Description: Natural lightning is both frequent and variable, and thus a good subject for statistical studies. A typical negative cloud-to-ground (CG) flash consists of multiple individual return strokes. The spatial and temporal distributions of various lightning events throughout the discharge provide a surrogate look inside the CG flash and offer insight into the underlying physical processes. In this study, we combine eight years of National Lightning Detection Network TM (NLDN) and North Alabama Lightning Mapping Array (NALMA) data to compute the spatial and temporal distribution of (i) subsequent NLDN-reported return strokes and (ii) LMA-reported sources, around NLDN-reported CG strokes. Subsequent strokes are separated into those with the same contact point as the first stroke, and those flowing along new lightning channels. Statistically, the distribution of strokes along new channels evolves deterministically, with ~200 km/s propagation speed from the original channel, comparable to the speed of a stepped leader. This suggests that the -CG subsequent strokes forming new channels may be directly linked to the initial one by a propagating leader inside the cloud. We present LMA case studies and a multi-year analysis of NLDN-LMA data that support this behavior. Our results are supported by ground-truth measurements and video recordings from previous field studies.