One of the many special experiences of spending a year on Macquarie Island are the sightings of some quite dramatic meteorological events. We experienced a beautiful sighting of rare noctilucent (“night time shining”) cloud on the 4th of January between midnight and 2 am. Noctilucent cloud forms below the mesopause region of the atmosphere at around 83 km altitude, when the temperature is below approximately -130°C. Normal high level cloud such as cirrus occurs at around 10 km altitude, so noctilucent cloud is approximately 8 times higher. They are visible after sunset or before sunrise when the sun has set on the tropopause (sun around 6 degrees below the horizon) but not on the mesopause region (sun around 16 degrees below the horizon).
The normal noctilucent cloud observing season is in summer (from November to February) in the southern hemisphere. At this time the mesopause temperatures are at the coldest. Over winter (from March to October) the mesopause is warmer with occasional colder periods, so a sighting of noctilucent cloud in winter would be a rare scoop! They are quite a rare sighting in summer too. Noctilucent cloud formation requires a combination of very low temperatures, a source of water vapour, and nucleii on which ice can grow such as meteor dust.
The other photos below show a dramatic day time storm passing over the Isthmus, depositing hail that soon melted.
The following graphs summarise the maximum and minimum temperatures experienced during 2019, in comparison to the averages. The 71 years of extremes (high and low) are also marked on the graph. The second graph looks at the rainfall accumulation for 2019. The years 2016 (record) and 2018 and the average are also included.
Finally, as this may be the last time the 2019 Met Team send a little hello via Icy News, we thought we’d share one of the fun times we have had as a team and the memories we take with us at the end of our season.
Warm wishes to all our family and friends back home.
Macquarie Island Bureau of Meteorology Team 2019