Annular Solar Eclipse
2013 May 10
|Western Australia||Northern Territory||Queensland||New Guinea and Solomon Islands|
|Global view||Bonriki, Kiribati||Tabuaeran/Fanning Island||Pacific View|
Climate Statistics for Locations along the Eclipse Track
Description of Table:
Percent of Possible Sunshine: the average number of hours of sunshine per day as a fraction of the total possible from sunrise to sunset.
Percent Frequency of ____ Clouds: the 20-year average frequency of the six cloud categories. The categories are derived from surface observations of cloud cover by automatic weather stations and by humans. "Clear" is defined as no cloud whatsoever, "few" is 1-2 eights of sky cover (called oktas), "scattered" is 3-4 oktas, "broken" is 5-7 oktas, and "overcast" is complete sky cover. "Obscured" refers to a surface-based obstruction (usually fog) that makes the sky invisible. Partly obscured is usually thin fog through which the sky can be seen, but it is treated as opaque here.
Calculated Cloud Amount: an arithmetical combination of the cloud amounts in the previous six columns. Obscured is treated as overcast. Monthy rainfall, days with rain, high and low temperatures: 20-30 year averages from surface weather observations.
Satellite-derived Average Cloud Cover Along the Eclipse Track
This map shows the average fractional morning cloud cover in May along the track of the eclipse, derived from 17 years of satellite observations of the globe. The nominal time of the observations is 7 a.m. Image: J. Anderson. Data: CIMMS/SSEC/University of Wisconsin.
Solar system geometry favours Australia once again, as the May annular eclipse revisits Queensland and the Northern Territory, nearly paralleling the path of the total eclipse of November 2012. This time, however, it embarks a little farther west, rising in mid-eclipse over the northern parts of Western Australia. For those wishing to catch this lunar-solar conjunction, Australia promises by far the best weather prospects.
In May, the southern hemisphere summer has given up and the season stands on the threshold of winter. The Earth's semi-permanent high-pressure zones have settled in at Australia's latitude, helping to bring the transition to the dry season. The Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ) have been nudged a little northward beyond the Australian continent. These two cloud and precipitation regions are caused by converging wind flows and are visible in the cloud cover map above. The ITCZ is the band of heavier cloudiness running eastward from the Philippines, while the SPCZ angles southeastward across New Guinea, past Fiji and Tonga. The two join together over Borneo. The upshot of all of this interplay of highs, lows, and convergent wind flows is that the eclipse track enjoys a marvellously sunny climate while over Australia but crosses into a much cloudier regime once it leaves the land and encounters both the SPCZ and the ITCZ.
The transition from sunshine to cloud is abrupt and dramatic. Over much of the outback interior of Australia, the table above shows that cloud amounts range between 25 and 35 percent. This climbs to between 40 and 50 percent along the Queensland coast, and then to between 60 and 70 percent over the Pacific Islands, though there are some parts of Polynesia that are more favourable than others, as can be seen in the satellite map of cloudiness in the table.
Tennant Creek and its environs in the Nothern Territory are the choicest places for the cloud averse, but just about any part of Australia will offer excellent weather prospects. At the challenging western edge of the track, in Western Australia where the Sun will rise in eclipse, average May morning cloud amounts generally range around 30 percent, giving good prospects for a horizon-bordered photo of a ringed, oval Sun.
from the Australian continent, the track touches Papua New Guinea and
the Solomon Islands, crossing the very cloudy climate along the SPCZ.
The cloud-cover map shows that this cloudiness lets up a bit as the shadow
reaches Kiribati, but the relief is short-lived, for the ITCZ lies in
waiting as the track stretches to its most northerly point. The one remaining
bit of land in the pathFanning Islandlies on the south edge
of the ITCZ, and though the path then moves into sunnier skies, only ship-borne
observers will be able to sample the late afternoon antumbral shadow.
Updated January 2013
Return to home page