DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

elease will make the loop shrink, and therefore
its current will augment in a way inversely proportional
to its size. By the end of the loop life,
the energy output due to this increased electromagnetic
power may supersede that in gravity
waves. In such a case, plasma in the vicinity of
the string loop will be subject to a strong radiation
pressure, and thus thin expanding plasma
shells will be generated. These dense gas shells
would then eventually be the loci for the formation
of galaxies and other structures.
While in standard scenarios cosmic strings
attract surrounding matter via their gravitational
fields, here instead string loops repel shells of
matter via electromagnetic pressure, forming
large-scale structures on the shell boundaries,
andvoidsintheshellinteriors. Thismodelisimportantly
constrained by present measurements
of distortions in the 3K cosmic microwave background
radiation, notably by the detectors in the
COBE satellite. See conducting string, cosmic
string, Witten conducting string.
Ottawa 10.7 cm flux The solar radio
flux observed at a wavelength of 10.7 cm (or
2800 MHz) by the Ottawa Radio Observatory
at 1700 UT (local noon) has been accepted as
a standard measurement of solar fluxes. Normally,
the flux is reported in solar flux units
(1 sfu = 1 × 10 −22 webers m −2 Hz −1 ) The
variations of the 10.7 cm flux, of 2800 MHz
flux as it is sometimes called, is closely associated
with enhanced thermal radiation from solar
active regions, and thus to the overall level of
solar activity.
outer core In geophysics, the Earth’s outer
core has an inner radius of 1215 km and an outer
radius of 3480 km. It is primarily composed of
molten iron with other components dissolved in
it. Convection in the outer core produces the
geodynamo that generates the Earth’s magnetic
field.
outfall A pipeline placed along the seafloor
to disperse wastewater into the sea.
outflow channel Very large dry river channels
seen on Mars. They typically begin in a region
of jumbled terrain (called chaotic terrain)
and cross terrain of various ages, often termi-
© 2001 by CRC Press LLC
overwash
nating in the lower-lying northern plains. The
channels have widths between 10 and 100 km
and are 400 to over 2000 km in length. Features
associated with outflow channels suggest formation
by catastrophic floods, probably caused by
groundwater breaking out of the source region.
Outflow channels are young, typically with formation
ages less than 3 × 10 9 years.
outgoing longwave radiation (OLR) Infrared
radiation emitted by the Earth toward
the space. The OLR displays strong temporal
and spatial variations, affected by surface
temperature, moisture, and clouds. The maximum
annual-mean OLR occurs over the Saharan
desert where the surface temperature is high
and the atmosphere is dry. Satellite-measured
OLR is used to determine the temperature and
hence the approximate height of clouds. Over
the tropics where heavy precipitation is caused
mostly by deep convection, OLR can be used as
a proxy of convective activity and precipitation
rate.
oval equation The partial differential equation
χ(u) ∂2
∂σ2
(1 +σ 2
1 +u2
)α+ +λ(u)
α
∂2α = 0
∂u2 for the unknown functions α =α(σ,u),χ =
χ(u) and λ = λ(σ). The field equation describing
stationary and axially symmetric spacetimes
in general relativity containing only electric
fields. Additionally, the cylindrical radius
function ρ given by
ρ 2 =
(1 + σ 2 )α −
3
1 + u2
αλχ
α
is required to be a harmonic function in these
solutions.
overtopping A term used to denote the process
of waves pushing water over the top of a
structure such as a breakwater or jetty.
overturning scale See Ozmidov scale.
overwash A term used to describe the flow of
water across a barrier island and into the bay behind.
An overwash fan of deposited sediments
generally results.
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