Northern Territory Radar Site Information
Alice Springs
Location: Alice Springs Airport (lat 23.82 deg S, long 133.90 deg 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 deg S, long 130.93 deg 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 approximately 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 attenuation 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
temperature 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 deg S, long 136.82 deg 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 deg S, long 132.45 deg 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
12 km 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 deg S, long 134.18 deg E)
Type: WF100 (C Band).
Availability (Typical): 2145-0500, 0600-0845, 0945-1430, 1530-2045 (CST).
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.