Are you aware that a cool anomaly over Northern Australia in part balances the current heatwave?

Do you hear this on the media? That taken Australia wide we have a cool anomaly in the north balancing to some extent the heatwave anomaly in the south east. So the continent as a whole does not have much of a warm anomaly on the 16th.

You can have fun making these anomaly maps at this useful BoM site – choose max or min & various periods. If you look at max and min anomalies for the weeks ending 7 Jan and 14 Jan – just eyeball the colours – IMHO Australia has not had a very high warm anomaly for the first half of Jan.
I read somewhere that the cool anomaly marks an area of descending air – hopefully we get an expert to comment.

This national radar image from 615am AEDT 18 Jan shows a low pressure system rotating into the deep interior – interesting to see Australia is not all heatwaves. Click on National Radar Loop here.
Forecast track at here.

8 thoughts on “Are you aware that a cool anomaly over Northern Australia in part balances the current heatwave?”

  1. That’s a monsoonal low or trough. What happens is surface heating causes rising air which pulls in moist air from the ocean. As humid is less dense than dry air the rising air continues to occur forming clouds and then rain.

    It’s cloud and rain which, which keep the temperatures down.

    Although the rainfall anomalies don’t match the temperature anomalies that closely. The discrepancy will be due to clouds that don’t form rain and perhaps the BoM’s infill algorithms, which create these maps from sparse data points.

    In the transition from the pre-monsoon to the monsoon itself temperatures drop substantially. I picked Rangoon as an example. The hottest month is April and average temperature drops 4C by July/August (NH mid-summer).

    Northern Australia is having an earlier/stronger monsoon than normal. And to some extent the East/South coast heatwave is due to pre-monsoon conditions extending further south than normal.

  2. Philip – So much of your commentary is wrong I really don’t know where to start. At the beginning I guess.

    “What happens is surface heating causes rising air which pulls in moist air from the ocean. As humid is less dense than dry air the rising air continues to occur forming clouds and then rain.” It is almost always hot September to May – if this was the sole cause it would always be this way. Try reading up on the MJO, equatorially trapped Rossby waves, and Kelvin waves. Humid air is slightly less dense than dry air – but try reading up on dry adiabats / moist adiabats for an explanation on convection.

    “And to some extent the East/South coast heatwave is due to pre-monsoon conditions extending further south than normal.” Huh? What do you mean by this?

    “Northern Australia is having an earlier/stronger monsoon than normal.” Snort. Darwin is well below average in rainfall for both December and January to date.. However it is fair to say the north western quarter of the continent has been much wetter than average, and the north eastern quarter has been much dryer.

    “Rain from this low is predicted to reach the south coast of WA by Wednesday. Expect large negative temperature anomalies across the West”. The forecast is for rain to extend into the SE – according to the BoM website. Temperatures forecast above average at Perth Wednesday, Thursday, Friday, Saturday, Sunday.


  3. I asked a meteorologist if he could add some content to the subject of the article and he has kindly emailed the following –

    The meteorology of the recent week is complex and the heat wave is an outcome of several processes.

    There is the basic observation that surface temperatures are higher when there are clear skies and low surface moisture: more incoming solar radiation and less evaporative cooling of the surface.

    Cloud (to reduce incoming solar radiation) and rain (to increase soil moisture) accompany the establishment of tropical monsoonal disturbances: easterly waves, tropical depressions, tropical cyclones and active monsoonal
    troughs. There has been an active monsoonal trough over northern Australian recently.

    Within tropical monsoonal disturbances there is major mass transfer of boundary layer air to high altitudes. In order for the monsoonal disturbance to be sustained there needs to be organised airflow to take the ascending
    air away, otherwise mass compensation means local subsidence and warming that suppresses the convection and disturbance. There has been persisting airflow from the northwest to southeast on the southern boundary of the
    persisting monsoonal disturbance (subtropical Jetstream) assisting the transport of upper troposphere mass from the monsoonal disturbance to higher latitudes, and its continuation.

    The dynamics of fluid flow on a rotating sphere cause vertical motions along the length of a jet stream, the direction and magnitude of the vertical motion depending on location with respect to the jet entrance and jet exit
    regions. The temperature and relative humidity charts at the time showed an extensive warm and dry band extending from the Timor Sea across South Australia and South-eastern Australia, and into the Tasman Sea. Such a band
    is consistent with subsiding air on the equator ward flank of the subtropical jet. The magnitude and location of the main centres of action varied with time and strengthened with the approach of cold air with an
    extra tropical disturbance from the southwest toward southeast Australia.

    In general terms, there was a fairly stationary (blocking) high pressure system over the Tasman Sea directing warm continental surface air over south
    eastern Australia bringing high surface temperatures to the region. This pattern, not uncommon in summer, was exacerbated by the outflow of upper troposphere air from the North Australian tropical disturbance strengthening
    the subtropical jet stream and enhancing the subsidence and warming of air middle tropospheric air. The jet stream was further strengthened as approaching cold air from the southwest tightened regional temperature and
    pressure gradients. The dynamic subsidence associated with the jet stream added to the warming and drying of low level air. The subsequent arrival of the cold air from the southwest, together with the development of a tropical storm in the Coral Sea that moved south into the Tasman Sea, weakened the blocking anticyclone and disrupted the jet stream dynamics. This allowed
    cooler air to spread across south eastern Australia.

    It should be noted that the pattern of blocking high pressure in the Tasman Sea and active tropical monsoon across North Australia had similarities with
    the pattern leading up to the Black Saturday fires of February 2009. There were also differences. However rare combinations of dynamic processes of the atmosphere can lead to extreme circulation features that occur infrequently.

  4. A description of the Australian Monsoon.

    Forecast for Eucla, which unlike Perth is on the south coast.

    Wednesday 22 January
    Cloudy. Areas of rain and the chance of thunderstorms. Possible heavy falls. Winds east to southeasterly 20 to 25 km/h, increasing to 30 to 40 km/h during the evening. Overnight temperatures falling to around 17 with daytime temperatures reaching the low to mid 20s.

    Eucla January rainfall average 12.9 mm. We are already well past that this year and a January record rainfall is possible with the forecast. I think we can safely say this is an unusual event.

  5. “Forecast for Eucla, which unlike Perth is on the south coast” – better check your forecast districts then. Eucla is in the SE of WA as I indicated. No comment on the substance of my response – surprising.

  6. Heavy rain through the Goldfields and Eucla over the past day and a bit – there will be large cool temperature anomalies through central and SE parts of WA. Perth is gradually getting cooler as the giant evaporative airconditioner to the east kicks in!

Leave a Reply

Your email address will not be published. Required fields are marked *