Category Archives: Weather

Global Warming at Home

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I checked out the Sydney weather this morning on the SMH Website (as you do on a Monday morning…). The site gives a nice snapshot of the forecast as well as historical statistics. As I cast my eye over the week’s forecast maximum temperatures (24°C, 26°C, 23°C, 21°C, 21°C, 22°C, 22°C) I was pleased by the mild weather. I then noticed the “Average Max” statistic for May: 19.4°C. A quick calc produced an average maximum temperature of 23.7°C for the next seven days! Hardly rigorous scientitific analysis, I admit, but still…

Needing any credible excuse to avoid starting the work week, I went off to Google to find long term temperature statistics for Sydney, which, as you would expect these days, are available on the WWW. Even more impressive, you can get it off the BOM’s “Climate Data Online” website. The oldest official data was recorded at Sydney’s Observatory Hill weather station and dates back to 1859 – only 150 years of data unfortunately. The first land-based observations were made by William Dawes, who arrived with the First Fleet in 1788. He built an observatory at Sydney Cove and for the next three years kept daily records of the wind, temperature, pressure and rainfall, but that’s another story…

Mean Maximum Daytime Temperature, Sydney 1859 to 2009

Mean Maximum Daytime Temperature

I wanted to do a bit more than just look at average maximums for the month, so I downloaded and analysed:

I calculated the mean, maximum and minimum temperatures for winter (May to August) and summer (November to February the following year) and added a trend line to each data set to show the 10-year moving average.

The daily maximum temperatures (lowest and highest for the month) aren’t all that useful, because they really are the outliers and, while the trend may be usefull, the scatter makes interpretation difficult. The monthly mean maximum temperatures shown above are very interesting though, particularly the maximums for winter.

There is no doubt it’s been getting steadily warmer over the last 150 years. The mean winter daytime maximum temperature is probably the most significant indicator and winters are definitely a lot milder now (10 year moving average of 19.2°C) than in the 19th century (16.7°C) . While there is a noticable “kick” upwards in the graph in the last decade, the rate of increase (2.5°C in 150 years or 0.017°C/per annum) appears to have been pretty steady though and I can’t really see an acceleration in the temperature rise during the past three of four decades (when greenhouse gas emissions were meant to have become the main contributing factor). In fact, if Sydney-siders had been paying attention to the climate instead of worrying about the Great Depression and WW1, they’d have been pretty anxious about the temperature increase during the period 1901 to 1927, when 10-year moving average maximum temperatures in winter increased by 2.3°C, from 16.0°C to 18.3°C.

Practical Range for HF Weatherfax Reception

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I spent a bit of time rigging a long-wire antenna at home today to see what sort of range is practical for HF Weatherfax reception:

  • The antenna is now about 20 metres long, made entirely from inexpensive hookup wire.
  • The antenna is L-shaped, with one leg oriented East-West and the other North-South.
  • I’ve also connected an earth wire to a copper stake just outside my window, significantly reducing background noise.

To my delight the little Degen DE-1103 receiver pulled in the Wellington MetService broadcast on two of the four frequencies! That’s 1,000 nautical miles! Local weatherfaxes from Charleville (WMC) are now clean and crisp.

HF Weatherfax received in Sydney from Wellington

HF Weather Fax Reception

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It hasn’t been really necessary on my last trip, being mostly within range of VHF weather forecasts, but getting offshore weather via HF WeatherFax has intrigued me.

If you’re carrying a notebook computer anyway, the only thing you need is an HF receiver with SSB (Single-Side Band) capability. Most people think megabucks when they hear “HF” and “SSB”, but a very inexpensive receiver will actually do the job. I bought a Degen DE1103 off E-Bay. You simply connect the output from the receiver to your notebook’s microphone input and then use one of the available software packages to decode the fax data received on the appropriate frequency at the given time! I use SEATTY from DXsoft, an amazing piece of software that literally does everything for you!

Receiving a fax using SEATTY

I was amazed at the ability of the little Degen DE1103 receiver (read some reviews here). Even at home, with the supplied 12 metre long wire antenna strung among trees, I can usually get quite clear fax reception. Out at Curlew Island one night, I strung the wire antenna from the forestay to the backstay, and found the receiver was overloaded with the sensitivity switched to “DX”. On “LO” I had perfect reception!

HF Weatherfax received with Degen DE1103 receiver and notebook running SeaTTY