How were the maps created?

Thunder-day data are recorded at a network of weather stations across Australia. The data from these weather stations are stored electronically in the Bureau of Meteorology's database called ADAM (Australian Data Archive for Meteorology).

The annual average thunder-day map is based on observed thunderstorm activity at about 300 weather stations over a ten year period (1990-1999). Thunderstorm occurrence at a particular location is usually expressed as the number of days in a calendar year when thunder was heard. These data were extracted from ADAM and a number of quality control checks were then applied to the data.

After the quality checks were applied to the data, an annual average was calculated for each of the weather stations. An objective analysis technique was then applied to these station averages to produce a regular gridded dataset covering Australia.

The lightning maps, which are based on eight years of satellite derived data (1995-2002), provide estimates of average annual lightning flash density information across Australia.

The lightning total flash density map and lightning ground flash density map are based on data from the Optical Transient Detector (OTD) and Lightning Imaging Sensor (LIS) for the Australian region. The analysis is based on eight years of combined OTD and LIS data. Data are acquired from polar orbiting satellites and are calibrated against the data derived from observations obtained by ground-based lightning flash counters. These data are in a gridded format.

Finally, the gridded data were visualised in a geographic information system and the colour maps created through this process.

About annual thunder-day and lightning flash density maps

Stations used in the analysis for thunder-days

The map below shows the thunder-day observing stations that were used to generate the average annual thunder-day map. The data from these observing stations were used to generate the gridded dataset, and the average map were derived from this grid.

Thunder-day, lightning ground flash and total flash density metadata

Annual thunder-day metadata

The following metadata summary and detailed metadata file provide information about the mean annual number of thunder-day gridded dataset. For example, information is provided about the format, spatial extent and analysis technique used to generate the grid.

TITLE:	Mean annual number of thunder-days.
DESCRIPTION:	Mean annual number of thunder-days in gridded format. The grid shows the number of thunder-days across Australia. The mean data are based on a ten year period 1990 - 1999.
CUSTODIAN:	Bureau of Meteorology
GEOGRAPHIC EXTENT NAMES(s):	Australia
AVAILABLE FORMAT TYPE(S):	ASCII row major, Arc/InfoTM grid export(.e00), Shapefiles.
SCALE/RESOLUTION	The resolution of the data is 0.25 degrees (approximately 25km)

Average annual lightning ground flash and total flash density metadata

The following metadata summary and detailed metadata file provide information about the mean annual lightning ground flash and total flash density gridded datasets. For example, information is provided about the format, spatial extents and analysis techniquase used to generate the grids.

TITLE:	Mean annual number of lightning flashes per square kilometre per year across Australia.
DESCRIPTION:	Mean annual number of lightning flashes per square kilometre. The grids show the number of lightning flashes per square kilometre per year across Australia in the form of two-dimensional array data. The mean data are based on a eight year period 1995 to 2002.
CUSTODIAN:	Bureau of Meteorology
GEOGRAPHIC EXTENT NAMES(s):	Australia
AVAILABLE FORMAT TYPE(S):	ASCII row major, Arc/InfoTM grid export(.e00), Shapefiles.
SCALE/RESOLUTION	The resolution of the data is 0.5 degrees (approximately 50km)