Time Machine: High Cloud Hastings Arc in China, 2012.02.22

The Hastings arc is among the rarest of all halos, even more so in high clouds. On Feb 22, 2012, XU Guodong was blessed with an outstanding display in Mohe, and became possibly the world's very first person to photograph a high cloud Hastings arc.

The display started in the morning and lasted for at least two hours till noon. XU happened to be on a road trip thus unable to document the event continuously from a fixed location. Most of his photos were taken at two stages of the display, when the sun was at around 15° and 22° respectively.

During the first stage, the typical sun-side Parry elements such as the Helic arc and Tape arcs were not particularly strong. However, the Hastings arc was fairly prominent and very easy to distinguish in unprocessed images. Had XU been equipped with the necessary halo knowledge, he would've recognize the arc at the scene with naked eyes.

Early stage of the display when the sun was at around 15°. 4-frame mosaic. Slightly enhanced. See if you can spot the Hastings arc.

Background subtracted version of the mosaic. The Hastings arc stands out nicely.

The original image to illustrate how prominent the Hastings was.

The display remained strong as the sun rose to 22° elevation, when XU made the second stop of his road trip. At this stage the Tape arcs improved a bit while the Helic arc disappeared. The Hastings arc, together with the Wegner arc, somewhat weakened but was still easily discernible in unprocessed images.

2-image mosaic. Slightly enhanced. Sun at around 22°.

Background subtracted version. Though weaker than during the first stage, the Hastings extends further towards the sun.

While the sky around the sun was jam-packed with great stuff, the opposite side was also very busy. The highlight absolutely goes to the loop-shaped Tricker arc. XU was very impressed by how the loop gradually shrinks in size as the sun rises.

Tricker arc (probably some Greenler and Trankle too) during XU's first stop. Sun at 15°.

Tricker arc during XU's second stop. 3-image mosaic. Sun at 22°. Note how the faint Subhelic arc goes above the 120° parhelia and then touches the upper end of the Tricker loop. The blue spot is quite strong too.

This display bears great significance in China's modern halo history. 10 years have passed and it still is unchallenged, and will likely remain so for a very long time.

Jia Hao