Bob Blog

Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.

Compiled Sunday 20August 2023

How big is the HOLE this spring?

During the dark of winter chemicals build in the air above Antarctica. When
sunlight returns at the end of winter and start of spring, between August
and October, this triggers chemical reactions which delete the Ozone
concentration in the Stratosphere. During the second half of last century
CFC gases were used in refrigeration and as a spray can expellant and vented
into the atmosphere triggering depletion of ozone over Antarctica every
spring-a phenomenon called the OZONE HOLE.

Scientific study of this depletion in the 1960 to 1980s lead to WMO
declaring the Montreal protocol in 1987 to phase out CFC. This is a rare
treaty that achieved universal ratification. It has been considered as a
success for the UN, and a sign that humans can mitigate planetary pollution.

However, this month observations show an earlier than normal depletion in
Antarctic ozone. If this continues, we may have as big a hole as in the bad
years around 2000. This time it isn't CFC to blame. The theory is that it
may be due to extra water vapour and some other gases from the Hunga -Tonga
/Hunga Ha'apai Volcano in January 2022. The blast produced a sonic boom that
travelled several times around the planet and a plume that rose 58km into
the Mesosphere and threw "unprecedented" amounts of water vapor into the
stratosphere.

In August 2022, a NASA report stated, ".as detected by NASA's Microwave Limb
Sounder.. The excess water vapor injected (into the stratosphere) by the
Tonga volcano... could remain in the stratosphere for several years... would
have a small temporary warming effect.... would not be enough to noticeably
exacerbate climate change effects."

Maybe this water vapor has found time during winter to build in the
Antarctic. In the stratosphere it acts as a "greenhouse" gas and reflects
infrared radiation in all directions, with that directed downwards warming
the surface. Sunlight converts some of it into hydrogen oxide molecules and
these destroy ozone.

Ozone absorbs UV and uses this to warm the stratosphere. The main effect of
an ozone hole is an increase in UV reaching the earth's surface and
consequential sunburn. Less ozone also means less warming of the
stratosphere from sunlight. A cooler stratosphere strengthens the polar
vortex, affecting the surface weather.

A good parameter to check out the polar vortex is SAM (or its proxy AAO)
At present it is negative, and that is consistent with a weak polar vortex.
So we shall watch the trends and see what happens with the Ozone hole over
the next few months.

TROPICS
It has been a busy week for cyclones and tropical depressions.
LAN visited Honshu Island in Japan. GREG and FERNANDA travelled west across
the North Pacific. HILLARY is threatening southern California and there are
two, maybe three tropical depressions in the Atlantic.

WEATHER ZONES
The South Pacific Convergence zone is expected to have a quiet week across
the northern Coral Sea to Samoa. A showery trough lingers well south of
Society Islands. Another is expected to form over the Fiji area by mid-week
and then go east fand fade over Southern Cooks.

Apart from these troughs it looks to be a good week for sailing from Tahiti
to Tonga.

HIGHS and LOWS

Low L1 is expected to deepen to around 985 near Chathams on Monday and then
spin clockwise and then go southeast, feeding cold showery weather on
eastern NZ.

HIGH H1 should form in the north Tasman Se by mid-week then fade.

Another Low L2 from the south Tasman Sea is expected to bring unsettled
weather to NZ this weekend.

A good week for getting westwards across the Coral Sea and North Tasman Sea

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