IX International Symposium on
Lightning Protection
26th
-30th
November 2007 – Foz do Iguaçu, Brazil
LIGHTNING CHARACTERISTICS ASSOCIATED TO SEVERE RAINFALL EVENTS, AROUND BELÉM–PA–BRAZIL
Arthur da Costa Almeida Brigida Ramati Pereira da Rocha UFPA UFPA
[email protected] [email protected]
José Humberto Araújo Monteiro José Ricardo Santos de Souza UFPA UFPA
[email protected] [email protected]
Gabriela Ribeiro Vieira Everaldo Barreiros de Souza UFPA UFPA
[email protected] [email protected]
Helder Tiago Sebastião da Cunha Williams Alan Pinheiro Souza UFPA UFPA
[email protected] [email protected]
UFPA (Federal University of Pará) - Rua Augusto Corrêa, 01 CEP 66075-110 - Belém - Pará – Brazil
Abstract - Lightning variables monitored by a LDN which includes 12 LPATS IV VAISALA sensors distributed over eastern Amazonia were analyzed during five severe rainstorm occurrences in Belém-PA-Brazil. These case studies referred to rainfall events, which produced more than 40 mm of precipitation totals, registered by a tipping bucket automatic pluviometer located at 1°24’ S, 48°26’ W. This instrument is placed at approximately 2.5 km from one lightning sensor installed at 1°24’ S, 48°27’ W. Centered at this location, a 20 km radius circle was drawn by means of a geographic information system, and the data from lightning occurrences within this area were set apart for analysis. The severe storm events selected occurred during: 09, 11, 27/January, 14/February and 02/March of 2007. This period corresponds to the beginning of the local rainy season of that year. The results show that lightning frequency of occurrences and peak current intensities rise substantially from a few minutes to more than one hour before intense rainfall occurs. The associated CG lightning events do not show a recognizable displacement pattern over the neighboring area. These case studies constitute a basis for future warnings of severe rainfall in Belém, other locations and seasons, in the Region.
1 INTRODUCTION The city of Belém is located on the southern shore of the
mouth of the Amazon River, about 150 Km from the
Atlantic Ocean. The daily tidal variation there reaches
over 2.5 m in the period between January and April. This
period coincides with the maximum rainfall accumulation
in Belém, brought about by the passage of the Inter
Tropical Convergence Zone (ITCZ) center axis over its
latitude.
Several days every year the maximum tide and severe
rainfall events occur simultaneously and flood the former
marshlands, nowadays taken over by the drainage
channels of the city, impairing traffic and resulting in
economic losses to the local people.
The losses would be reduced if the civil defense were able
to warn people of the situation, through the local
communications media.
With this purpose a project involving several operational
and research local institutions (UFPA, SIPAM, SECTAM,
INMET), and the Civil Defense agents, is being carried
out. This paper is part of a joint effort to use
meteorological information, including lightning detection
capabilities, to develop an alert system of severe rainfall
events in Belém, especially during the critical months
mentioned above, seeking to lessen the disturbances
caused by flooding in the city.
The Amazonian Protection System (SIPAM), lightning
detection network, includes 12 LPATS IV VAISALA
sensors, four of which, installed in Belém, Breves,
Paragominas and Tucuruí, are less than 350 km from one
another, therefore reasonably covering the area of interest.
This system monitors continuously the lightning
occurrence rate, number of strokes per flash, flash type,
stroke polarity and peak currents, as well as their time of
occurrence in microseconds.
This information associated to severe rainfall events
registered by a tipping bucket automatic rainfall gauge
operated by the Brazilian National Meteorological
Institute (INMET) in the city, might give some parameters
related to lightning produced by the same clouds, early
enough to warn the local population.
The relationship between lightning parameters,
precipitation and the convective meteorological systems
producing them has been studied by several methods. [1]
and [2], used satellite images, [3], [4], [5] and [6], used
radar, air borne balloon rawinsondes plus LDN at the
surface, to study the relation between lightning parameters
and precipitation in Taiwan, U.S.A. and Spain. In the
Amazon region, particularly around Belém, the first
attempts to estimate rainfall, from the lightning frequency
of occurrence were made by [7] and [8]. The installation
of the SIPAM’s LDN represent an opportunity to advance
these applied studies, locally, with improved technology
of lightning location.
2 MATERIALS AND METHODS
Intense rainfall events which produced more than 40 mm
of accumulated precipitation measured by a tipping bucket
pluviometer (Campbell Instruments, Inc) of an automatic
meteorological surface station located at 1°24’S; 48°26’
W, were selected for analysis. This data collected by
INMET showed that events satisfying this condition
occurred during days 09, 11, 27 of January, 14 of
February and 02 of March, 2007. Lightning data obtained
through SIPAM’s LDN and processed by VAISALA’s
LTrax software in Belém, provided the input to a
geographic information system ArcGIS which separated a
sub set of data, of lightning occurrences within a 20 km
circle drawn around the sensor located at 1°24’S,
48°27’W in Belém.
This sub set of lightning data collected during the above
mentioned days of intense rainfall events was the object
analysis for this paper.
3 RESULTS AND DISCUSSION
Figure 1 shows the time behavior of the lightning
frequency of occurrence and the hourly average
precipitation in Belém, during five intense rainfall events
registered on the days indicated.
Even though the time of occurrences vary significantly,
one observes the lightning frequency of occurrence
exceeds 8 flashes per 10 min intervals and its peaks
preceded the rainfall maxima in all these cases.
A summary of the lightning and rainfall data analyzed is
presented on Table 1. One observes at Table 1 that,
considering only five events of intense rainfall it was not
possible to establish a statistical threshold for the
lightning frequency of occurrence associated to them.
Figura 1 - Lightning rate of occurrence versus average hourly
rainfall in Belém.
Table 1 – Lightning and Rainfall data – Belém-PA-Brazil – Case Studies
Overall 381 lightning flashes were detected during the
events analyzed. 197 occurrences were detected
simultaneously by more than four sensors of the system.
The stroke peak currents ranged from 11 to 186 kA and in
all cases studied, the number of negative CG lightning
exceed that of the corresponding positive strokes.
It appears that there was a positive, but yet undetermined,
relation between the ratio of CG to CC events number and
the accumulated rainfall in Belém.
Perhaps the most interesting fact displayed in Table 1 is
that, lightning occurrences within a 20 km radius around
Belém, preceded intense rainfall by 20 to 70 minutes. If
some lightning parameter threshold is established by
future studies, this time interval would become useful to
warn the local population when that situation would occur
simultaneously with high tide periods in Belém.
Fig 2 shows the lightning occurrences within the 20 km
circle drawn around the LPATS IV sensor position in
Belém.
The color coded dots represent each one of the five days
analyzed. One observes, as expected, a higher occurrence
of events over land surfaces, compared to the water
surfaces. Other than that, there was no clear pattern
observed for the time evolution of the lightning individual
events.
It seems that they occurred randomly and not as if some
cloud system were drifting over this area, during the
intense rainfall occurrences.
Fig 2 – Keraunic map showing the distribution of occurrences of
lightning during five events of intense rainfall in Belém–PA–
Brazil.
4 CONCLUSIONS
Lightning parameters observed around Belém-PA during
five events of intense rainfall in this city, were analyzed.
All events occurred between 16 and 22 hours UT or 13
and 19 hours, local time. It appears that the rainstorm
clouds originated themselves within or near a 20 km circle
around the city, since lightning flashes showed no clear
sequence of spatial displacement during all cases studied.
It was not possible yet to establish threshold values of the
lightning parameters indicative of the lightning
occurrences. This may be attributed to the relatively small
number of events analyzed so far.
A preliminary result indicates that a positive relationship
existed between the ratio of numbers of CG to CC
lightning occurrences and the precipitation totals observed
in each case. Further study is necessary however to
confirm this observation.
For all cases analyzed, lightning occurrence frequency
peaked from 20 to 70 minutes before intense rainfall
hourly events.
This delay seems a promising parameter to be considered,
for a future alert system of intense rainfall occurrences in
Belém.
5 ACKNOWLEDGEMENTS
The authors wish to thank the Brazilian Financier of
Studies and Projects (FINEP) for the support provided to
an applied research project in which they are involved.
They also thank Mr. José Raimundo de Sousa, Director of
INMET’s 2nd
District for facilitating access to rainfall
data.
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