NAMMA Lightning ZEUS Data

Table of Contents

Introduction
Campaign
Network Description
File Naming Convention
 Data Format and Content
Contact Information

Introduction

The NAMMA Lightning ZEUS data are provided by World-ZEUS Long Range Lightning Monitoring Network. The NASA Science Mission Directorate funded the Zeus network to provide lightning detection and location observations in the African continental and maritime region during the NAMMA experiment. This network has been funded by the National Science Foundation (Water Cycle Program), with joint support by the Hellenic General Secretariat for Research and Development, Univeristy of Nevada, State University of Ceara, University of Sao Paulo and Companhia de Energia Eletrica do Estado do Ceara. Lightning data is obtained from "sferics" (Very low frequency radio receivers), located at thirteen ground stations spread across the European and African continents and Brazil. Lightning activity occurring over a large part of the globe is continuously monitored at varying spatial accuracy (e.g. 10-20 km within and >50 km outside the network periphery) and high temporal resolution (1 msec). Time is determined by the Arrival Time Difference (ATD) between the time series from pairs of the receivers.

Campaign

These data files were generated during support of the NASA African Monsoon Multidisciplinary Analyses (NAMMA) campaign, a field research investigation sponsored by the Science Mission Directorate of the National Aeronautics and Space Administration (NASA). This mission was based in the Cape Verde Islands, 350 miles off the coast of Senegal in west Africa. Commencing in August 2006, NASA scientists employed surface observation networks and aircraft to characterize the evolution and structure of African Easterly Waves (AEWs) and Mesoscale Convective Systems over continental western Africa, and their associated impacts on regional water and energy budgets. For more information about the NAMMA Campaign, go to the NAMMA web site: http://namma.nsstc.nasa.gov/

Network Description

Zeus long-range lightning detection system is based on detection of sferics - the impulsive radio noise emitted by a lightning strike - in the Very Low Frequency (VLF) spectrum between 7 and 15 kHz. In the VLF portion of the radio spectrum sferics propagate thousands of kilometers through the earth-ionosphere waveguide. This lightning detection system, built by Resolution Displays, Inc., consists of a network of thirteen Very Low Frequency (7-15 kHz) radio receivers spread over the European and African continents.

Each receiver reports the vertical electric field as a time series which represents the sferic's waveform, and includes a time stamp synchronized by the Global Positioning System (GPS) clock. The Arrival Time Difference (ATD) between the time series from pairs of receivers is extracted by time correlation. Each ATD yields an elliptic locus-of-points on the earth's surface for the lightning location, and the intersection of several ellipses from a sferics candidate defines a ''fix'' location. The European receivers are situated in Birmingham (UK), Roskilde (Denmark), Iasi (Romania), Larnaka (Cyprus), and Evora (Portugal), and the African receivers are in Addis Ababa (Ethiopia), Dar es Salaam (Tanzania), Bethlehem (South Africa), Osun state (Nigeria), Dakar (Senegal), Guadeloupe, Fortaleza (Brazil) and Sao Paulo (Brazil) .

Additional information about the ZEUS network can be found here.

File Naming Convention

Each file represents a 15 minute timeframe of lightning data, with the time embedded in the file name as the starting time. The files are distributed as tar compressed files named as

namma_zeus_yyyy-mm-dd.tar.gz

Thes files uncompress and contain multiple files named according to the example shown below:

namma_zeus_yyyy-mm-dd_tttt.dat

where, yyyy is the year, mm is the month, dd is the day, and tttt is the starting time.

Data Format and Content

The data were reprocessed in October 2009 and an adiitional field was added. The file format is shown below. The PI documentation also contains the data format adn additionally hte Fortran format to read the data and coordination infomation for rx locations. These data are arranged in ASCII data files, space delimited, and each file supplies data for a 15 minute period of time.

Below is the a line of a data file shown as an example.

Example data:

2008 10 12 23 0 4 23439 -4.18725 -72.13458 3642 15.6 0 3 5 10 0 0 0 0 0 0 0 0 0 1 1 1 1 1

Where each column of the ZEUS data file is defined below:

Column 1: year
Column 2: month
Column 3: day
Column 4: hour (GMT)
Column 5: minute
Column 6: second
Column 7: mili-second
Column 8: latitude
Column 9: longitude
Column 10: major ellipse error of the ATD solution (m)
Column 11: ATD error in micro-seconds
Column 12: Quality control (0,1,2)
Column 13: Polarity (0,1,2,3) (+-)
Column 14: Number of Rx employed in the Solution (4,5,6,7)
Column 15: Number of ATD pairs employed in the Solution (6-21)
Column 16: UK rx
Column 17: Denmark rx
Column 18: Romania rx
Column 19: Cyprus rx
Column 20: Athens rx
Column 21: Portugal rx
Column 22: Ethiopia rx
Column 23: Tanzania rx
Column 24: South Africa rx
Column 25: Nigeria Rx
Column 26: Daka Rx (rx not available)
Column 27: Guadeloupe (French Island-Caribean) Rx
Column 28: Fortaleza-Brazil Rx
Column 29: Sao Paulo-Brazil Rx

Major ellipse error: This represents the major axis of the ellipse error that circumscribes the ATDs. The lower the value, the better the solution. (This error is still under analyses, so don't take too much in consideration, use the ATD error instead).

ATD error: This represents the Residual Error of the ATD solution. The values lower than 20 micro-seconds are considered acceptable, and it is expected to have low location errors according to the theoretical model.

Quality control: It a simplification of the ATD error/Major Axis that is
used to diagnose the location accuracy: 0-Good; 1-Questionable;
2-Bad

Polarity: It is the retrieved ELF polarity (+ or -), where the values represent
confidence level (1-low; 2-median; 3-high) and 0 no confidence
The values of -9 means that the polarity was not available in the reprocessing.

Number of Rx: It tells how many receivers were employed in the solution

Number of ATDs: It tell how many ATDs were used in the solution. If we had
4 rx, we have a maximum of 6 ATDs (combination of 4, 2 a 2); 5 rx
have 10 ATDs, 6 rx have 15 ATDs and 7 rx have 21 ATDs. The ATDs
employed in the solution passed a quality control, and if it does
not pass, it is not used. So, you might have some solutions that
did not used the maximum number of ATDs according to the number of
rx available

The Columns (15-28) Indicate which receivers were available (1) or not (0).
In this data set we have only the African and American receivers
available, i.e., Ethiopia, Tanzania, South Africa, Nigeria, Guadeloupe
Fortaleza and Sao Paulo.

Contact Information

Questions related to these data should be directed to the data provider listed below:

Carlos Augusto Morales Rodriquez
morales@model.iag.usp.br

To order these data or for further information, please contact:

Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: ghrcdaac@itsc.uah.edu
Web: http://ghrc.nsstc.nasa.gov/