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Thanks to all who have been providing a fair degree of discussions on
optical phenomena in the Philippines. I am learning a lot and getting
new insights. Would like to comment on a thread that's been going on
that's been started by Chris and Timo:
>You are right about this, the key factors are the low temperature and
>high vater vapour partial pressure. These conditions are mainly the
>result of vertical motion in an atmosphere. In tropical atmosphere, most
>of the significant vertical motions are associated to convective
>disturbations such as thunder clouds, while in mid- and polar latitudes
>forced ascend/descent by frontal processes play the most important role
>(I take it that you know the basics). What I have seen here in Finland,
>typical ice clouds (cirrus, cirrostatus) are usually much wider spread
>and better formed when generated by frontal activity...
This is interesting. Thunderstorms often develop during the May to June
period here, and this type of cloud do punch a hole vertically as they
ascend, and given the high humidity (unghh) and lots of water in the area
(being tropical and all), convective clouds could really be the reason we
see a lot of optical phenomena this time of the year.
>> Second, tropical conditions may more often result in extensive
>> lower-atmosphere cloud development, which may then tend to obscure
upper
>> atmosphere halo-generating clouds.
>
>... So one would think that northern latitudes would be more benefical
>to Halo observations. However, one should note that typical midlatitude
>weather system (cyclone) has a period of 3-5 days. One may see pretty
>neat haloes when the system is arriving, but then the lower clouds tend
>to block the view. Ice clouds formed from convective clouds
>(cumulogenitus, cumulonimbogenitus), on the other hand, has no such
>drawback, at least if they are not connected to a typhoon. Thus, it is
>reasonable to conclude that one could actually see more halos in
>tropical region, but perhaps not that well formed displays. This is the
>conclusion Marko Riikonen made, if I remember right. Anyway, I want to
>point out that our atmosphere is pretty complicated system and I
>concentrated on only a few key factors. Thus, this should not be taken
>as a general truth (especially because it is several years since I have
>studied these phenomena).
>>
Interesting. A lot of the halo phenomena and pearlescent clouds I've
been seeing the past few days are found in clouds in the foreFRONT (pun
intended) of bands of dark clouds. As the sun gets blocked and the
lower clouds advance, the phenomenon disappears. Two weeks ago, I
took a morning plane trip to go south, and whenever I encountered high
clouds during the flight, I saw halos around the sun (about twice during a
one-hour trip south). This occured prior to my seeing a really intense
and colorful halo display on the ground after lunch.
Now that we are in the middle of a band/front, the skies are dreary and
no light displays are seen. No typhoons yet.
Jun
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< Jun Lao, Editor, the Appulse >
< The Philippine Astronomical Society >
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