David Dodd 2:33 a.m., May 19
Temperature Inversions, Tides, Sunrise/Sunset, and the Leonid Meteor Shower
Low-lying temperature inversions commonly occur in San Diego as winter approaches. During the night and morning hours, a meterological condition often occurs in which the normal higher-you-go-the colder-it-gets trend is reversed. At such times cold marine air lies below a stable layer of warmer air originating from inland locales. Whenever moist air is trapped below a low-lying inversion layer, dense fog forms on or near the ground, and San Diego International Airport is sometimes forced to suspend operations.
November's and December's picturesque sunsets and sunrises are no accident. This is the time of year when high cirrus clouds, often the precursors of storms, sweep through our area with some regularity. When cirrus or other lofty clouds are present, low-angle sunlight bathes the undersides of these clouds in a crimson luminescence. This effect is most noticeable a half hour to a few minutes before the sun rises and a few minutes to a half hour after the sun sets.
Highest and lowest tides this month occur on the same day: Friday, November 14. From a high of +6.9 feet at 8:48 a.m., the tide level drops to -1.5 feet at 4:02 p.m. During the lunch hour the tide will be ebbing at the rate of nearly two vertical feet per hour. Visit a gently shelving beach, such as Coronado's, to watch the water recede with almost every breaker. November's string of extreme low tides are perfect for tidepool gazing. They include a -1.2 foot tide at 2:26 p.m. on Wednesday, the 12th; a -1.4 foot tide at 3:12 p.m. on Thursday; a -1.4 foot tide at 4:02 p.m. on Friday; and a -1.2 foot tide at 4:56 p.m. on Saturday. The Saturday low tide, however, takes place after sunset.
The annual Leonid meteor shower, famous for its outbursts over the period 1998-2002, has now settled down to a modest display of only about 10-20 visible events per hour (as seen under clear, dark skies). This year the peak period is Monday morning, November 17, generally after midnight. However, this year the moon, only four days past full, will significantly flood the sky with stray light. All Leonid meteors appear to radiate from the constellation of Leo, which currently lies high in the south at dawn.