Positive Peak Currents Research Articles

Novel n-octadecylcarboxamide CoPc: amperometric detections for bioanalytes using modified GCE

Here, we are reporting cobalt(II) phthalocyanine (CoPc) containing the active catalyst for the electrochemical investigations of bioanalytes. The synthesized tetra-n-octadecylcarboxamide cobalt(II) phthalocyanine was characterized by FT-IR, UV, TGA, mass and powder XRD analysis. In the present work, the synthesized complex was characterized by cyclic voltammetry and shows the redox behaviour corresponding to central metal (Co+II/Co+I) of the complex. Three biomolecules are well separated by their oxidation peaks in simultaneous detections of AA, DA and UA at 170, 350 and 550 mV with increasing high positive peak current. The low detection limit of AA, DA and UA was 40, 30 and 30 µmol by CV methods. The modified tetra substituted CoODAPc/GCE exhibits an excellent electrocatalytic activity, stability, high sensitivity, good linearity and selectivity without losing its catalytic activity and proves to be a versatile chemical sensor for commercial pharmaceutical samples, vitamin C tablets and dopamine injections.

Five-year study of cloud-to-ground lightning activity in Yunnan province, China

The characteristics of cloud-to-ground (CG) lightning in Yunnan province, based on the data recorded by the Yunnan Lightning Detection Network (YNLDN), are presented. The data, more than 2.09million CG flashes, cover the entirety of Yunnan province and were recorded from 2006 to 2010. The spatial analyses (total and positive flash density, the percentage of positive flashes, negative and positive peak currents) were done with a resolution of 20km. The average spatial distribution shows a maximum (3.8flasheskm−2yr−1) over the central Yunnan province and Jinsha river associated with topography and cold air mass passage. The mean monthly variation shows a maximum CG lightning between May and October (94%) and minimum values in December and January. High values (0.15flasheskm−2yr−1) for positive CG lightning density are observed in Red river basin. The monthly distribution of positive flashes shows a main maximum in April (19%) and a secondary maximum in July and August (17%), suggesting that positive flashes tend to occur earlier in the year than total flashes. The mean annual percentage of positive flashes has lower values at 3% in the central parts of the province. The percentage of positive CG flashes changes over the year from 2% in August to 49% in January. The monthly variation of median peak current for the negative first-stroke for each month varies only slightly from 27kA. The monthly variation of the median peak current for positive first-stroke, however, has a maximum in winter and the minimum occurs in May. The mean diurnal cycle for the negative CG lightning flashes peaks between 1600 and 1700 LT (11.37%) and shows a minimum between 0900 and 1000 LT (0.23%). The diurnal variation of positive flashes, in turn, shows a maximum around 0100–0200 LT, with a secondary peak at 1800 LT. This variation is associated with local mesoscale circulation, which has an obvious nocturnal feature.

Exceptional cloud-to-ground lightning during an unusually warm summer in Yukon, Canada

[1] The 2004 lightning season and related wildfire activity in Yukon, Canada, was exceptional in many aspects. The synoptic environment during the summer was dominated by a persistent upper level ridge over Alaska and Yukon, bringing above-normal temperatures and below-normal precipitation to Yukon. The number of cloud-to-ground (CG) flashes, lightning-initiated forest fires, and extent of the area burned exceeded historic records. Forest fire smoke affected most of Yukon during the summer. Thunderstorms forming in this northern environment in July exhibited unusual lightning characteristics as detected by Canadian Lightning Detection Network. Changes in the frequency of extreme lightning days and in the fraction of nocturnal lightning occurrence were observed. Lightning properties in July differed from climatology in several ways. The central regions of Yukon experienced enhanced positive CG lightning activity. First-stroke positive peak currents were found to be stronger, while negative peak currents were weaker than climatology. Our observations are consistent with the previous findings reported in southerly climates. Although thunderstorms related to the diurnal heating and cooling cycle influenced positive lightning occurrences in Yukon, other possible sources, including pyrocumulonimbus clouds and inverted-polarity thunderstorms, cannot be overlooked. Evidence is presented suggesting that both atmospheric conditions and smoke from the fires may have influenced the electrification process of thunderstorms to enhance +CG production. The extreme summer of 2004 experienced in Yukon may provide a hint of future impacts due to climate change.

The North American Lightning Detection Network (NALDN)—Analysis of Flash Data: 2001–09

Cloud-to-ground (CG) lightning data have been analyzed for the years 2001–09 for North America, which includes Alaska, Canada, and the lower 48 U.S. states. Flashes recorded within the North American Lightning Detection Network (NALDN) are examined. No corrections for detection efficiency variability are made over the 9 yr of the dataset or over the large geographical area comprising North America. There were network changes in the NALDN during the 9 yr, but these changes have not been corrected for nor have the recorded data been altered in any way with the exception that all positive lightning reports with peak currents less than 15 kA have been deleted. Thus, the reader should be aware that secular changes are not just climatological in nature. All data were analyzed with a spatial resolution of 20 km. The analyses presented in this work provide a synoptic view of the interannual variability of lightning observations in North America, including the impacts of physical changes in the network during the 9 yr of study. These data complement and extend previous analyses that evaluate the U.S. NLDN during periods of upgrade. The total (negative and positive) flashes for ground flash density, the percentage of positive lightning, and the positive flash density have been analyzed. Furthermore, the negative and positive first stroke peak currents and the flash multiplicity have been examined. The highest flash densities in Canada are along the U.S.–Canadian border (1–2 flashes per square kilometer) and in the United States along the Gulf of Mexico coast from Texas through Florida (exceeding 14 flashes per square kilometer in Florida). The Gulf Stream is “outlined” by higher flash densities off the east coast of the United States. Maximum annual positive flash densities in Canada range primarily from 0.01 to 0.3 flashes per square kilometer, and in the United States to over 0.5 flashes per square kilometer in the Midwest and in the states of Louisiana and Mississippi. The annual percentage of positive lightning to ground varies from less than 2% over Florida to values exceeding 25% off the West Coast, Alaska, and the Yukon. A localized maximum in the percentage of positive lightning in the NALDN occurs in Manitoba and western Ontario, just north of North Dakota and Minnesota. When averaged over North America, first stroke negative median peak currents range from 19.8 kA in 2001 to 16.0 kA in 2009 and for all years, average 16.1 kA. First stroke positive median peak currents range from a high of 29.0 kA in 2008 and 2009 to a low of 23.3 kA in 2003 with a median of 25.7 kA for all years. There is a relatively sharp transition from low to high median negative peak currents along the Gulf and Atlantic coasts of the United States. No sharp transitions are observed for the median positive peak currents. Relatively lower positive peak currents occur throughout the southeastern United States. The highest values of mean negative multiplicity exceed 3.0 strokes per flash in the NALDN with some variation over the 9 yr. Lower values of mean negative multiplicity occur in the western United States. Positive flash mean multiplicity is slightly higher than 1.1, with the highest values of 1.7 observed in the southwestern states. As has been noted in prior research, CG lightning has significant variations from storm to storm as well as between geographical regions and/or seasons and, consequently, a single distribution for any lightning parameter, such as multiplicity or peak current, may not be sufficient to represent or describe the parameter.

A Cloud-to-Ground Lightning Climatology for Romania

Abstract The first study of the characteristics of cloud-to-ground (CG) lightning in Romania, based on the data recorded by the Romanian National Lightning Detection Network (RNLDN), is presented. The data, more than 1.75 million CG flashes, covers the entirety of Romania and were recorded between January 2003 and December 2005 and January and December 2007. The spatial analyses (total and positive flash density, the percentage of positive flashes, and negative and positive peak currents) were done with a resolution of 20 km. The average spatial distribution shows a maximum (3.06 flashes km−2 yr−1) over the south slopes of the central meridional Carpathians possibly associated with the Romanian Plain convergence zone. The mean monthly variation shows maximum CG lightning between May and September (98%) and minimum values in December and January. High values (>0.028 km−2 yr−1) for positive CG lightning density are observed in southwestern and central Romania. The monthly distribution of positive flashes shows a main maximum in May (25%) and a secondary maximum in August (23%), suggesting that positive flashes tend to occur earlier in the year than total flashes. The mean annual percentage of positive flashes has lower values at 1.3% in the central parts of the country. The percentage of positive CG flashes changes over the year from 1% in June to 19% in January. The monthly variation of the median first-strike peak currents has a maximum in winter and reaches a minimum in July, for both negative and positive currents. The mean diurnal cycle for total CG lightning flashes peaks between 1230 and 1430 UTC (2.2%) and shows a minimum between 0600 and 0800 UTC (0.3%).

Characteristics of cloud‐to‐ground lightning in severe and nonsevere storms over the central United States from 1989–1998

Over a region from the Kansas/Colorado border to Minnesota, previously associated with positive anomalies in the mean annual positive cloud‐to‐ground (CG) lightning percentage and positive peak current, we describe significant differences in the properties of CG lightning flashes between warm‐season severe (i.e., large hail or tornado producing) and nonsevere storms. The percentage of CG lightning flashes lowering positive charge to ground was substantially higher in severe storms (i.e., up to three times higher). The median positive peak current in severe storms was significantly larger (i.e., by about 25%). Finally, the median negative peak current in severe storms was very low (i.e., as low as 12–16 kA) and was noticeably smaller than in nonsevere storms (i.e., by at least 10%). Severe storms appeared to be significant producers of positive CG lightning in the anomaly region (AR). Up to 30%–70% of warm season positive flashes in the AR were associated with severe storms. Only 2%–30% of negative flashes were associated with severe storms in the AR. As a result, the mean warm season (and likely annual) positive anomalies in positive CG percentage and peak current are likely associated with a unique class of severe, organized storms that occur preferentially in this geographical region. We found substantial differences in the properties of CG lightning flashes associated with severe storms in other regions. For example, the mean warm season properties of CG lightning associated with severe storms in the region of peak large hail and tornado activity (e.g., Oklahoma) were fundamentally different (i.e., significantly lower positive CG percentage, lower positive peak currents and higher negative peak currents) compared to severe storms over the AR from western Kansas to Minnesota.

Cloud-to-Ground Lightning Activity in the Contiguous United States from 1995 to 1999

The spatial and temporal distributions of cloud-to-ground lightning are examined over the contiguous United States from 1995 to 1999 using data from the National Lightning Detection Network. Annual flash density, annual lightning days, cumulative frequency distributions of daily flash counts, and annual and summertime diurnal distributions of lightning are documented. The spatial, annual, and summertime diurnal distributions of positive and negative polarity cloud-to-ground lightning are also documented. Over the same five-year period, the production of positive and negative lightning is examined over two case study areas located in the northcentral United States and along the Gulf Coast, centered on Sioux Falls, South Dakota, and Fort Rucker, Alabama, respectively. Case studies include radar‐lightning analyses of significant lightning episodes from 1996. Maximum flash densities and lightning days are found over coastal regions of the southeastern United States. Other prominent maxima are seen over parts of the southern Rocky Mountains and adjacent High Plains. Cumulative frequency distributions indicate that throughout the contiguous United States roughly 10% of the days with lightning accounted for 50% of lightning production. The majority of lightning was produced during summer (June‐August) throughout the contiguous United States, except over the south-central United States and along and near the Pacific coast. Summertime lightning activity over the western and eastern United States exhibited a diurnal cycle with maximum frequencies in the afternoon to early evening. Over the central United States, summertime lightning activity was complex with significant longitudinal variations in daily activity and a tendency to occur at night. Over most of the contiguous United States, a larger fraction of negative lightning was produced during summer than positive lightning, and the diurnal cycle of positive lightning lagged the diurnal cycle of negative lightning by up to two hours during summer. The main exception to these behaviors occurred over an area in the northcentral United States extending from the Colorado‐Kansas border to western Minnesota. Over this area, positive lightning peaked during midsummer versus late summer for negative lightning, and the diurnal cycle of positive lightning also peaked up to several hours prior to the maximum in the diurnal cycle of negative lightning during summer. In addition, this area was characterized by maxima in the percentage of positive lightning and positive mean peak current. The maximum in the percentage of positive lightning over the north-central United States was caused by a dramatic increase in positive flash density to the east of the Rocky Mountains and a local minimum in negative flash density over the area described above. Results from the Sioux Falls case study indicate that positive lightning was produced primarily during summer in the hours around sunset by isolated storms and convective lines in various stages of mesoscale convective system (MCS) development. These convective events usually contained one or more storms that were characterized by predominantly positive lightning, high positive flash rate, and large positive peak currents. Negative lightning activity was produced later in the summer and throughout the night by more mature convective systems arranged in lines or clusters. Over Fort Rucker, positive and negative lightning was produced throughout the year, by diurnally forced storms during the warm season and by MCSs with areally extensive stratiform regions during the cold season. Diurnally forced storms (MCSs) were characterized by a low (high) percentage of positive lightning.

Cloud-to-Ground Lightning in the United States: NLDN Results in the First Decade, 1989–98

The physical and geographical characteristics of over 216 million cloud-to-ground lightning flashes recorded during the first decade (1989–98) of operation of the National Lightning Detection Network (NLDN) covering the entire continental United States are presented. These characteristics include the total cloud-to-ground flash density, the positive flash density, the percentage of positive flashes, the first stroke negative and positive peak currents, and the multiplicity for negative and positive flashes. All analyses were done with a spatial resolution of 0.2° corresponding to an approximate resolution of 20 km. Flash densities were not corrected for detection efficiency; the measured values are presented. The maximum measured flash density is found to exceed 9 flashes km−2 across Florida in the Tampa–Orlando–Cape Canaveral corridor, near Fort Myers, and between Lake Okeechobee and the Atlantic Ocean. The mean monthly flash count peaks in July at approximately 5.5 million flashes. Positive flash density maxima, greater than 0.4 flashes km−2 occur in southern Florida; Houston, Texas; and along the Texas–Louisiana border. A broad region of relatively high positive density also occurs throughout the Midwest. The mean monthly positive flash count peaks in June and July at approximately 240 000 flashes in each month. The annual mean percentage of lightning that lowered positive charge was highest in the upper Midwest, exceeding 10% or 20% throughout most of the region. High percentages are also characteristic along the West Coast. The annual percentage of positive lightning has increased from 3% in 1989 to approximately 9% in 1998. The authors believe the increase is the result of improved sensor detection capability in the past decade. The mean monthly percentage of positive lightning flashes ranged from 4% in August to 17% in December for the decade. The annual median negative peak current ranged from 30 kA in 1989, decreasing steadily to about 20 kA in 1998. The annual median positive peak current ranged from 55 kA in 1989 decreasing to about 22 kA in 1998. The annual median peak negative and positive currents have approximately the same value since 1995, the first year after the NLDN upgrade. The monthly median first stroke peak currents for the decade peak in the winter and reach a minimum in May (positive current) and July (negative current). The mean monthly negative multiplicity for the decade ranges from 2.1 in February to 2.5 from June to October. The mean monthly positive multiplicity is approximately 1.2 throughout the year. The diurnal variation of the maximum flash rate over land was examined and found to peak during 1200–2000 local time (LT) with an exception for the upper Midwest, which peaked during 2000–0400 LT. Over water surrounding the continental United States, the lightning flash rate peaks primarily in the morning hours from 0400 to 1200 LT.

Cloud‐to‐ground lightning in southeastern Brazil in 1993: 1. Geographical distribution

About 1.1 million cloud‐to‐ground lightning flashes were recorded by a lightning positioning and tracking system in southeastern Brazil in 1993. The 1‐year continuous lightning data set is the first obtained in Brazil. It has been analyzed for geographical distribution of total flash density, percentage of positive flashes, negative and positive flash densities, and negative and positive flash peak currents. The dependence of the flash density and peak current on latitude, altitude, and soil resistivity was investigated. Negative flash peak current was found to be inversely correlated with latitude, but no other significant correlation was found for flash density and peak current with these parameters. Positive flashes were found to be contaminated by intracloud flashes. The maximum total, negative, and positive flash densities were 15.5, 9.1, and 7.7 flashes/km2 per year, respectively. The average percentage of positive flashes was 36.5%. The geometric means of negative and positive peak current were 30.9 kA and 17.8 kA. The high density, high percentage and low average peak current of positive flashes found in this study are probably a result of such a contamination. Neglecting positive flashes below 15 kA, assuming that they correspond to intracloud flashes erroneously identified by the system, the maximum positive and total flash densities would be 3.9 flashes/km2 per year and 11.7 flashes/km2 per year. The percentage and geometric mean peak current of positive flash would be 23% and 38.7 kA, respectively. The results are discussed in the context of other similar measurements made at different parts of the world.

Comments on “Large Peak Current Cloud-to-Ground Lightning Flashes during the Summer Months in the Contiguous United States”

The recent paper by Lyons et al. (1998) reports on large peak current lightning flashes recorded by the National Lightning Detection Network (NLDN) during 14 summer months in four years, 1991–95. Lyons et al. examine, arbitrarily, only flashes with peak currents higher than 75 kA. It is an important contribution. High peak current flashes of positive polarity, for example, have been shown to be associated with sprites and elves in the stratosphere and mesosphere. The purpose of this note, however, is to emphasize that ground truth for negative return stroke peak currents exists only up to 60 kA and this is for triggered lightning (Idone et al. 1993, Table 1). No ground truth exists for return stroke positive peak currents. Despite this problem, we are still justified in making peak current estimates as long as the limitations are recognized. I quote from Lyons et al. (1998, p. 2227) and add explanatory comments:

On-state decay in NbO2: Relationship to recombination and to nonlinear I-V

When addressed with a 1-MHz sinusoidal or triangular wave signal, the on-state of NbO2 shows two regimes of conductance. The lower-conductance regime occurs over the voltage range less than the holding voltage and shows, for the most part, superlinear I-V characteristics. Decay studies indicate that the time interval in this low-conductance or lower-current subregime is an inverse linear function of the on-state mobile charge density. This study also indicates that the subsequent positive peak current is also an inverse linear function of the time interval in the lower-conductance subregime of the previous cycle. The nonlinear lower-current subregime of the on-state I-V characteristics is thus directly related to the decay of the charge density of the true on-state, the decay being induced by a critical time duration of subholding voltage conditions. It is hence believed that the lower-current regime is a consequence of a relaxation-induced trapping phenomenon, and that the recovery of the high-conductance true on-state metal-like regime is due to the field-induced liberation of electrons from trapping centers. These data reinforce our earlier contention that both a critical charge concentration and a critical electric field intensity are inseparably necessary to maintain the on-state in NbO2.