Brisbane Rain Radar Upgrade

Brisbane (Marburg) weather radar site will soon receive an upgrade with dual-polarised Doppler radar technology that will enhance image clarity while monitoring real-time rainfall and wind conditions in real time.

Marburg radar, located 53 kilometres west of Brisbane GPO, provides an outstanding overview of precipitation across Queensland. However, its ability to detect low level rainfall over Greater Brisbane may be restricted due to Great Dividing Range and Lamington Plateau obstructions.

Reflectivity

Raw radar reflectivity values can be extremely difficult to work with, ranging from tiny drops of raindrops to hail during severe thunderstorms. To make them more useful, radar processing converts these raw values to logarithmic scale and provides us with units called dBZ for reflectivity units.

dBZ values can be seen on a radar image in one of two colors depending on whether the radar is operating in clear air mode or precipitation mode; depending on which mode is selected, green will indicate clear air while yellow stands for precipitation mode.

Mt Stapylton rain radar provides coverage across most of South East Queensland; however, its ability to detect rainfall over the Great Dividing Range and Lamington Plateau to the west and south of Brisbane may be restricted, leading to missed detection of low-level virga (precipitation that falls above its footprint but does not reach the ground). Radar processing may be negatively impacted by hills, buildings or solid objects reflected off solid objects.

Melting layer

Radar meteorology’s bright band symbolizes a layer where solid precipitation is melting away into raindrops with lower reflectivity than ice because of their different dielectric properties. This process accelerates nearer the surface of the ML, producing higher velocity and narrower spectral width.

The ML is located approximately 3000m above sea level and extends in an arc from Evans Head to Tin Can Bay, being limited by visibility due to Great Dividing Range in the west and Lamington Plateau in the south.

Clutter

This radar site, located 8km east of Mount Isa City on a hill 501m above sea level with the tower standing 22m taller, provides ideal monitoring conditions for rain-bearing systems that affect catchments and valleys of Warrego and Maranoa River basins. Views to seaward are generally unimpeded except at certain ranges due to an obstruction from Telstra’s communication tower in SSE direction.

NEXRAD (Clutter Identification and Mitigation) (CDM) radar is well placed to detect tropical cyclones as they move across the Coral Sea, as well as track rain depressions, troughs, and fronts that approach from inland. However, coastal shower activity and sea clutter during windy conditions where rough sea surface reflectivity may obscure light inshore showers. Clutter identification is a critical aspect of radar data processing because misidentifying ground-clutter echos as precipitation could result in overestimation or biased velocity estimates – however its fuzzy logic algorithm effectively separates ground-clutter echoes from zero-velocity narrow spectrum weather echoes to ensure data processing accuracy.

Squall line

The radar is located well to detect rain over Brisbane and has a wide arc to the north, east, and south. Unfortunately, its range can be reduced due to obstructions such as Lamington Plateau in the west and Evans Head in the south, reducing radar’s range significantly and leading to missed returns and clutter.

Squall lines are clusters of thunderstorm cells connected by shared precipitation cores or mass. Squall lines often feature damaging wind gusts, often accompanied by dark cloud-covered shelf clouds.

The Squall Line product provides an illustration of precipitation’s velocity relative to either moving towards or away from a radar (radially). When precipitation moves towards the radar, its color scale changes from negative and blue to positive and yellow when perpendicularly approaching it; two radar “tilt angles” (0.5deg and 1.45deg) are available as options for this product.