DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

and the surface gravity is
κ = c2
4GM .
For r − <
I > 2 )/ < I > 2 ] 1/2 and I is the signal intensity
with indicating time-averaging, is the most
commonly used parameter for characterizing the
intensity fluctuations. Scintillation occurring in
the Earth’s ionosphere is usually observed on a
transionospheric satellite communication link.
There are two terrestrial regions of intense scintillations:
at high and low latitudes. At high latitudes,
scintillation frequency and intensity are
© 2001 by CRC Press LLC
seafloor magnetic stripes
greatest in the auroral oval, although it is also
strong over the polar caps. Geomagnetic storms
may cause scintillation to increase at any phase
of the solar cycle. At low latitudes, nighttime
scintillation shows its greatest range of intensity,
with both the quietest and most severe of
conditions being observed. The source of the
scintillation is the irregularities on the walls of
spread-F bubbles and is most prevalent during
solar maximum. It may cause peak-to-peak fluctuations
on 1.5 GHz and can be of the order of
56 dB above the geomagnetic equator, and as
high as 20 dB for hours at a time in the equatorial
anomaly region. At mid-latitudes scintillation
is less severe and is positively correlated
with spread-F and, to a lesser degree, with sporadic
E. Interstellar scintillation, arising from
similar mechanisms on a much larger scale, is
ubiquitous in radio observations of pulsars. See
spread F.
Scorpius X-1 The brightest X-ray source
in the sky, identified with the spectroscopic binary
V818 Scorpii at 16 h 19 m 55 s , −15 ◦ 38 ′ 2 ′′ .
V818 Scorpii has a magnitude range of 11.80
to 13.20 with period 0.787313 days. The X-ray
source has variations with the same period, and
quasiperiodic oscillations of approximately 165
sec.
scour The process by which flowing water
removes sediment from a seafloor, lake, or river
bed. Typically most pronounced where engineering
structures such as piles or jetties meet
the seafloor.
scri (I , Script I) Null infinity in an
asymptotically simple or weakly asymptotically
simple space-time. See asymptotically simple
space-time, weakly asymptotically simple
space-time.
sea The ocean, or a smaller body of salt water.
Also used to describe the locally generated wind
waves.
seafloor magnetic stripes Alternating bands
of magnetic polarization found in the seabed
floor. The Earth’s magnetic field reverses with
a period of hundreds of thousands of years.
Seafloor spreading from the central seafloors oc-
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