Seasonal matters

 This will cover a fair range of topics noticed since we returned to Mallacoota.

The first shows a gathering of birds on a sandbank in the Inlet.  Most of them are Crested Terns but a few waders are also present.  The green arrows point to a few Bar-tailed Godwits, mainly to emphasise the smaller size of the Red Knots (orange arrows).

A clearer shot of the Knots.

I went for a ride to Stingray Point to check for Topknot Pigeons and any other fig munchers.  None present, but a lot of action in a flowering eucalypt. This is one of several Red Wattlebirds.

A Little Wattlebird moons a Laughing Kookaburra.

Across the District the Pittosporum is coming in to flower

As is Clematis aristata: in this case ascending a fig tree.

Some figs: I don't think they are quite ripe yet.

Pink eucalypt flowers.

I think these are also eucalypt flowers but they were well on to a private garden.

The following morning (15 September) was notable for the difference in temperatures across 2 BoM sites and my Weather Station.

This can be explained by wind at the airport coming off the cold mountains while at Gabo it's coming off the (relatively) warm sea.

The search for Topknot Pigeons continued on the 16th with a visit to the Radley Place fig tree.

The figs here also need a little more time to ripen, so no Pigeons, Figbirds or large Cuckoos.

An enormous succulent flower: my guess is that if fully erect it would be at least 3 m high.

I went down to the Inlet looking for a Lewin's Rail near the Boardwalk.  Not present, but a perched Azure Kingfisher was a good alternative,

Frances recalled that last year there had been an excellent floral display along the Narrows so we went t check that out.  It was pretty good, including this Clematis.

A few orchids, beginning with Caladenia catenata.

Not an orchid, but both members of the pea family - Hardenbergia violacea and Platylobium formosum.

Diuris pardina.

Pterostylis pedunculata (Maroonhood)

Another pea - Glycine clandestina.

The only Heron seen was a White-faced heron.

An interesting clump of fungi.

Minima at Mallacoota and Gabo Island

On a Weather Forum in which I post I wrote on 13 May:

 The BoM site is showing a minimum of 6.8C at 0640 - and may get a little lower. The surprising value is the minimum for Gabo Island at 11.2C at 0557. I know Gabo is surrounded by relatively warm sea but that seems a very large difference over such a short distance especially with wind at all sites coming from WNW.

One response to this was 

Quite similar thing happens here, I'm 2km from the coast and the min was 6.9°C morning (identical to yesterday's), yet the min at Bellambi (6km NNE and right on coast) was 12.0°C with a land breeze all night. The ocean does make a big difference to minimums.

So I thought I should investigate a bit further.  Using the excellent Climate Data Online facility at BoM I got a year's minimum records (taking 2019 as sufficient for my needs) for the two sites (Mallacoota # 084084, hereafter Airport, and Gabo Island #084016, hereafter Gabo) to see how they compared.

I omitted any days on which  either site didn't report a minimum giving me 330 records.  There were 35 null values for Gabo one of which was also blank for the Airport.  The correlation coefficient between the two series was strong at 0.935.  As would be expected from that a scatterplot of the two series shows a good significant trend.

Very few of the observations were identical.  The average difference (Mallacoota-Gabo) was -1.8^oC.  Disregarding sign the average difference is  2.0 ^oC.

The great majority of the differences are between +1^oC.  and -4^oC.   They are summarised in this chart, with the red-hot snowflake indicating the approximate position of the reading of 13 May.  So it was a relatively large negative difference!

It is still a little surprising that there are such differences between two sites within ~16.5 km.  The airport site is 200 m from the sea and 22 m elevation and I suspect the Gabo site is a similar distance and 15m elevation.

The wind direction at both sites was similar on the night between 12 and 13 May, mainly WNW with the speed a little higher (~20 kph) at Gabo than the Airport (11 -15 kph).  Perhaps the wind coming across a few kilometres of sea warmed it up?

The only other difference I can think of is that there some buildings on Gabo - but I think ~50 m from the screen.  At the airport the screen is in an open paddock (covered with mown heath in 2019) with no nearby buildings and the nearest substantial vegetation over 100 m away.

Heat waves in Mallacoota

In my recent weather report for January 2020 I commented on the number of heat-wave days in the month.  I thought it might be interesting to look back at the longer term picture of this type of weather.

To recap, the BoM defines a heat wave as:

3 or more consecutive days of temperatures significantly above average.  

I calculated the average maximum for each month and the standard deviation of the average and then defined the threshold for a heat wave as average +1SD.  I rounded these values down which makes a slightly lower threshold which compensates for the cases where there are 2 days above the threshold and the third is only 1 degree below.  This gave my temperature thresholds as >25^oC for November - March and I don't regard a temperature below 25^oC as worthy of being part of a heat wave.

The threshold values were:

In terms of perception of unpleasant weather the length of the heat wave is (IMHO) a significant contributor: a heat wave lasting 6 days is more than twice as unpleasant as a 3 day wave.  So rather than counting the number of heat waves count Heat Wave Days  which I define as a day that contributes to a heat wave.   Note that this can span the end of a month: a situation such as 30 Jan =30^oC;  31 Jan =30^oC; 1 Feb = 28^oC would count as a heat wave with 2 days in January and 1 in February.

Looking over the period of BoM records for Mallacoota (since 1994) the total number of HWD by month is shown below, which seems sensible.

 Looking at the total number of HWD for each Summer (eg 1994 represents the period November 1993 - March 1994) gives a jagged line which while appearing to have an upwards trend this is far below statistically significance.

I wouldn't want anyone to get excited about this statement as being an argument against climate change. 

1. It is a very short series;
2. The measure I have used may lack some rigour (eg is +1SD the correct measure to use in calculating the threshold?); and
3. The airport site often shows a much lower minimum than sites in town as the sea-breeze cuts in in the afternoon so may be biased to not record extreme temperatures.

However I think it is an interesting perspective.

Is Autumn finally here?

Around 0630 on 26 April the temperature was 11.2 on my Davis (and a little cooler at the BoM site) with 95% rH,  This gave a picturesque fog over Karbeethong.

 Looking to the East there was a good lot of colour in the sky!

Some weather averages

The catalyst for this post began with a view that it is much windier at Mallacoota this year than we have noticed in the past.  I then discovered a table of monthly averages including 9am windspeed.

Comparing the values for 2019 to date with the previous averages for Mallacoota shows that in fact this year is a little below past averages!

So I wondered whether the difference was due to comparison with Canberra.  An initial issue was that the current Canberra Airport data doesn't include the average windspeeds which I find astonishing - surely that would be a crucial measure for an airport.  However, nothing that Canberra Airport does - that might save them a few bucks - should surprise anyone.  Fortunately the data is available for the Airport Comparison site although it closed in 2010.  Yes, Mallacoota is windier!

While browsing the daily observations for Victoria on 9 April I noticed in passing that Wilson's Promontory had recorded a gust of 102kph.  Yowza!  So I looked up the average wind speeds for that location: for both 0900 and 1500 it is pretty much a steady 30kph through the year!  That is about double Mallacoota!

My second lot of averages are daily average temperatures for April.  I have calculated these from the BoM data on Maximum and Minimum temperatures for Mallacoota.  The catalyst for this was observing that for March the average mean temperatures hardly moved across the month.  Did the same apply to April?

No siree!  Whether one looks at the average for each day or the cumulative (ie month to date) series there is a pretty fair drop across the month,  Obviously, the cumulation process smooths the series out so has a higher correlation coefficient.

I have added in the daily values for 2019 which shows a pretty consistent high average.  That may be about to change, but thus far the difference between current mean temperature up to 7 April is 1.7C above the long term average.