Northern Territory Information

Alice Springs

  • Location: Alice Springs Airport (lat 23.82° S, long 133.90° E)
  • Type: WF100 (C-Band).
  • Availability (Typical): 2145—0215; 0345—0815; 0945—1415; 1545—2015 (CST).

Interpretation Notes

The Alice Springs radar has a very good view to the south of the airport. The coverage is from 260 degrees (True) through the south to 075 degrees (True) - this area includes: Tempe Downs, Angus Downs, Kulgera, Finke and the western edge of the Simpson Desert. The effectiveness of the radar is reduced markedly to the north by the MacDonnell Ranges which lie between the Airport and Alice Springs Central Business District. In the north, the area of good coverage lies from Mt. Hay in the west to Mt. Yambah in the north to Harts Range in the northeast.

Due to the relative high cloud base normally associated with shower, storm and rain events, intensities in the low ranges must be considered suspect. In normal circumstances, there is a large amount of dry air beneath the clouds and this causes a certain amount of evaporation of the precipitation. In the 0.0 to 0.2 mm range, most of the precipitation does not reach the ground (virga); in the 0.2 to 2.0 mm range the actual rainfall is generally closer to 1.0 mm mark, however, in the higher ranges, rainfall rates are usually fairly accurate.

Being a C-Band radar, if there are large thunderstorms around, the radar may not be able to detect accurately the strength of other storms located behind the closest storms. This may also lead to the underestimation of the strength, at times, of very intense isolated storms. Heavy rain over the radar itself will reduce the reliability of the radar in all directions.

Darwin/Berrimah

  • Location: approximately 7 km southeast of Darwin Airport (lat 12.46° S, long 130.93° E)
  • Type: WSR 74 (C-Band).
  • Availability (Typical): 24 hours per day Intermittently used for research purposes so may be unavailable for some extended periods.

Interpretation Notes

The Berrimah radar is located on a rise with the dish antenna tower mounted app roximately 50 metres above the surrounding topography. It has a good coverage in all directions up to a range of 250 km with the following two exceptions: (a) some local masking of echoes at low elevations to the east; (b) some signal blockage to the north-northeast due to several HF transmitter towers.

Heavy rain over the radar site will cause attenuation of all signals. Path atte nuation also occurs when the radar beam passes through an intense thunderstorm cell; the returned signal from cells further along that path will be reduced. Because the beam width of this particular radar is only 0.9 degrees, it may 'undershoot' high level storms and rain echoes may appear less intense than actual rainfall rate.

During the dry season from May to September, when low level atmospheric tempera ture inversions are more prevalent, images may display areas of relatively strong (Level 2 or 3) permanent echoes. These tend to be reflections from coastal features; commonly from Gunn Point and the Cobourg Peninsular northeast of the radar, and from the nearside coastline of the Tiwi Islands to the north. Also during this time of the year, a false image of the Timor coastline may sometimes be seen extending northwest from Bathurst Island. This phenomenon is due to second skip returns at multiples of the radar's maximum range.

Gove

  • Location: Gove Airport (lat 12.28° S, long 136.82° E)
  • Type: WF100 (C-Band).
  • Availability: 2130—0815, 1030—1415, 1530—2115 (CST).

Interpretation Notes

The Gove radar has a nearly unrestricted view in all directions. Local topography can produce a single weak false echo immediately adjacent the radar centre to the southeast.

During the wet season, thunderstorm tops will be visible out to the effective range of the radar at around 250km although smaller showers frequently associated with these storms will not be visible at that range. Tropical cyclones may be seen during the wet season months November to April, although lesser category 1 cyclones may not be sufficiently developed to be easily discernable. The higher category tropical cyclones will display rain echoes in spiral bands rotating about a central clear eye with the highest intensity rainfall about the eye. The structure of the cyclone in the arc facing the radar centre will be seen, although the far side will be less clear due to the weakening of the radar signal by heavy rain (attenuation). The closer the cyclone is to the radar centre the clearer the structure will be viewed.

Rain showers during the dry season are common; most frequently moving from east to west, often in organized lines (known as Gulf Lines) orientated approximately north-south. Cooling after midnight during the dry season frequently results in false echoes (Anomalous Propagation) appearing over the land as isolated weak areas with sometimes up to 80% coverage. These echoes are identified by their random appearance and disappearance between sequences with no general direction of movement and total dissipation after sunrise. They only appear over land and are displayed as the weakest level echoes.

Katherine/Tindal

  • Location: RAAF Base Tindal, 20 km east-southeast of Katherine. (lat 14.51° S, long 132.45° E)
  • Type: WSR81C-8 (C-Band).
  • Availability (Typical): 24 hours per day

Interpretation Notes

The Tindal radar is located on a small hill and offers a good view in all directions and no permanent echos are evident.

The appearance of "false echoes" or Anomalous Propagation (AP) is generally limited to occasions where there are significant temperature inversions (in normally stable conditions) in the lower atmosphere. AP can fluctuate rapidly from one image to the next as the inversion is forming or dissipating, however, it has a quite static appearance and can normally be distinguished from "real" echoes which exhibit some movement and a definite life cycle of development and decay.

RAAF aircraft operating in the area, particularly to the west and southwest, can drop "chaff" which will give a weak radar return. Such echoes normally dissipate quickly, seldom lasting longer than 15 to 20 minutes.

The radar can suffer some attenuation loss during heavy precipitation events. In these instances, the leading echoes are normally displayed at "true" intensity, while trailing echoes may be displayed at a lower intensity due to some loss in signal strength.

It is rare to observe echoes at a range greater than 300 km. The display of echoes at 300 km is indicative of the upper structure of a storm exceeding 12km in height, however, echoes from storms at that distance may not display accurate intensities since the radar beam is generally directed above the most intensive part of the storm.

Tennant Creek

  • Location: Tennant Creek Airport (lat 19.64° S, long 134.18° E)
  • Type: WF100 (C-Band)
  • Availability (Typical): 24 hours per day

Interpretation Notes

Geographical Aspects

The radar at Tennant Creek is situated just to the north west of the township. Approximately 3km north-east of the radar site lies a low range of hills which form part of the McDouall Range. These hills run east to west reaching 430m above mean sea level. This is about 50m above the level of the radar, blocking the radar's horizon. "Two Tank Hill", 200m from the radar site, and running east to west, obscures most of the horizon to the south. In all other directions the radar has a clear skyline.

Meteorological Aspects

The effect of the obstructions to the north-east and south will be most noticeable with shallow wide spread rain. If these rain echoes are moving, they will appear to weaken or completely disappear when they move 'behind' the hills, only to appear again once they move out of behind the obstructing hills. Wet season thunderstorms and rain-bearing depressions, which extend to great heights, will be able to be detected and tracked in all directions while they are above the radar's skyline.

Non-meteorological echoes

In most cases, processing of the radar signal removes permanent echoes caused by hills, buildings and other solid objects, but sometimes a few slip through. These show up as small, stationary patches of very light rain, mostly along the higher ground. Under stable atmospheric conditions in the dry season, anomalous propagation may cause these patches of stationary echoes to be more prominent or increase in number.