CLIMATOLOGY OF AIR-SEA ENERGY EXCHANGE

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CLIMATOLOGY OF AIR-SEA ENERGY EXCHANGE
SW
LW
Latent heat
Sensible heat
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CLIMATOLOGY OF AIR-SEA ENERGY EXCHANGE
Ocean surface heat balance H SW? - LW?
- Qh? - Qe? 0 100 65
8 27
Net heat flux
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CLIMATOLOGY OF AIR-SEA ENERGY EXCHANGE

• Ideally the globally integrated surface net flux
  should converge to zero. Uncertainties of the
  heat exchange through the ocean bottom and heat
  inflow/outflow with rivers and underground water
  are small.
• Major features of the net flux fields
• Spatial patterns are more comparable with surface
  sensible and latent fluxes, which are not zonal
  in contrast to SW and LW radiation.
• How to produce the flux field?
• Individual variable information
• Correction of data, use of metadata
• Selection of schemes
• Computation of fluxes
• Composition of the fields (averaging)

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Basic surface meteorological parameters Sea
surface temperature A general definition of sea
surface temperature (SST) is that it is the water
temperature at 1 meter below the sea surface.
However, there are a variety of techniques for
measuring this parameter that can potentially
yield different results because different things
are actually being measured. The sea surface
skin temperature (SSST) is the temperature that
physically determines the surface heat fluxes. It
may be measured radiometrically from ships and
other in situ platforms, and by satellite-borne
radiometers provided the atmospheric effects are
properly corrected. The cooling due to sensible
and latent heat fluxes and the longwave emission
occurs at the skin, whereas the shortwave heating
is distributed over a greater depth. Thus, most
of the time, the SSST is colder than the water
just beneath the skin, typically by a few tenths
C. This difference increases with increased
surface cooling and decreases with increasing
wind speed.
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For traditional bulk formulae the transfer
coefficients have been determined with respect to
the bulk SST, so for application of these
formulae, this would be a more appropriate
temperature to use. For the bulk formulae which
use the transfer coefficients derived from
surface renewal theory the skin temperature is
the appropriate value.


Bucket SST measurements
Infrared radiometer


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Ship SST data are obtained mostly from Engine
Room Intake (ERI) thermometers or (about 1/3 of
the modern data) from SST buckets. A small but
increasing number of ships use hull contact
sensors which, if carefully calibrated, appear to
give the most consistent SST data (Kent et al.,
1993a Emery et al., 1997). ERI SST data are
warmer under most conditions, on average by 0.35C
although there is significant scatter about this
typical value. Bucket measurements are found only
to be biased compared to hull values during sunny
daytime conditions when they gave on average SST
values about 0.3C warmer. This is more likely
due to the buckets heating on deck prior to use
rather than to near surface ocean heating. VOS
SST correction All engine intake samples, when
identified, should be reduced by 0.35C, otherwise
- default reduction by 0.2C

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• Air temperature
• For atmospheric temperature and humidity, the
  most accurate instrument is a psychrometer (wet
  and dry bulb thermometer) whose measurements are
  based on well-established thermodynamic theory.
• The most critical requirements to attain its
  potential accuracy are
• adequate ventilation of air past the sensing
  elements
• (3 - 4 ms-1 flow rate),
• to ensure the full wet bulb depression, and
  adequate shielding
• from solar radiation.
• This usually means a double shield with the space
  between also ventilated. Basic accuracy depends
  on the type of sensing element used for the
  familiar sling and Assman psychrometers this is
  the precision of the particular mercury-in-glass
  thermometer, 0.1C at best.

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The exposure of thermometer screens on the VOS
varies from good (e.g. screens hung on stanchions
on the outboard rails of either bridge wing) to
very bad (e.g. "the screen is made of brown
varnished wood and fitted to the side of the
wheelhouse in the 'porch' of the bridge wing on
the port side"). The poorly exposed sensors are
about 0.5C warm. During the day all the sensors
showed increasingly warm readings with increasing
solar radiation. For the better exposed sensors
this bias was up to 2C for the poorly exposed
sensors the mean bias reached over 4C. Air
temperature correction ?Ta
(2.7-0.064urel) SW / 1000
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Humidity The wet and dry bulb psychrometer is
the traditional meteorological instrument for the
routine measurement of temperature and humidity.
In general, however, psychrometers are not
suitable for continuous routine measurement of
atmospheric humidity at sea in stand-alone or
automatic mode because of their need for
attention (e.g. washing salt from the wick,
replenishing the water reservoir). Dewpoint
hygrometers are also based on sound thermodynamic
theory, measuring the temperature at which a film
of dew forms on a cooled mirror, but are
generally too complex to serve as operational
instruments. Their main use in air-sea studies is
as a reference standard accuracy of 0.2C in
dewpoint is readily achievable (corresponding to
0.2g/kg-1 at about 22C).
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Humidity - more The VSOP-NA results showed that
psychrometers produced lower (and therefore
presumably more accurate) dew point readings
compared to screens. Since the ship may often be
a source of heat but is rarely a significant
source of water vapour, shipboard humidity
readings may be of better quality than the
temperature data. Correction of the humidity
(dew point temperature) For unaspirated screen
measurements Tdew 1.029Tdew - 1.080, where
prime denotes the corrected dew point
temperature. One-third of this correction is
applied if no information is available about the
method of humidity measurements
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• Wind speed
• 1. Anemometer winds.
• In general are considered to be most
  accurate, if
• The anemometer is properly installed onboard
  the ship
• True wind is properly computed from the
  relative wind
• (both requirements
  normally are not the case)
• 2. Beaufort estimates of wind
• Less accurate, but more homogeneous

RV Darvin
Flow distortion by the ship superstructure
Laboratory and numerical modeling can help
identify biases in the measured wind speed. It is
difficult to derive flow distortion effects for
all ships.
RV Knorr
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Beaufort wind estimates
Rear-Admiral, Sir Francis Beaufort, Knight
Commander of the Bath, was born in Ireland in
1774. He entered the Royal Navy at the age of 13
and was a midshipman aboard the Aquilon. Beaufort
is said to have had an illustrious career on the
seas and by 1800 had risen to the rank of
Commander. In the summer of 1805 Commander
Beaufort was appointed to the command of the
Woolwich, a 44 gun man-of-war. It was at this
time that he devised his wind force scale. An
early surviving form the scale is replicated
below. By 1838 the Beaufort wind force scale was
made mandatory for log entries in all ships of
the Royal Navy. Beaufort last served as
Hydrographer to the Admiralty. He died in 1857
two years after his retirement.
In 1854 the English and French were entrenched in
fighting at Sevastopool. The fleets carrying
almost all their winter supplies was struck by an
intense, early winter storm on the morning of
November 14. In response to the losses and with
the hope that there might be some way to forecast
future storms, the British Admiralty and the
French Marine jointly sponsored a weather network
-- the ancestor of the World Meteorolgical
Organization -- to provide storm warnings. And
here then is when Sir Beaufort's scale begins its
protean growth.
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Figures to Denote the Force of the Wind Figures to Denote the Force of the Wind Figures to Denote the Force of the Wind Figures to Denote the Force of the Wind
1 Light Air Or just sufficient to give steerage way. Or just sufficient to give steerage way.
2 Light Breeze Or that in which a man-of-war with all sail set, and clean full would go in smooth water from. 1 to 2 knots
3 Gentle Breeze Or that in which a man-of-war with all sail set, and clean full would go in smooth water from. 3 to 4 knots
4 Moderate Breeze Or that in which a man-of-war with all sail set, and clean full would go in smooth water from. 5 to 6 knots
5 Fresh Breeze Or that to which a well-conditionedman-of-war could just carry in chase, full and by. Royals, c.
6 Strong Breeze Or that to which a well-conditionedman-of-war could just carry in chase, full and by. Single-reefed topsails and top-gal. sail
7 Moderate Gale Or that to which a well-conditionedman-of-war could just carry in chase, full and by. Double reefed topsails, jib, c.
8 Fresh Gale Or that to which a well-conditionedman-of-war could just carry in chase, full and by. Treble-reefed topsails c.
9 Strong Gale Or that to which a well-conditionedman-of-war could just carry in chase, full and by. Close-reefed topsails and courses.
10 Whole Gale Or that with which she could scarcely bear close-reefed main-topsail and reefed fore-sail. Or that with which she could scarcely bear close-reefed main-topsail and reefed fore-sail.
11 Storm Or that which would reduce her to storm staysails. Or that which would reduce her to storm staysails.
12 Hurricane Or that which no canvas could withstand. Or that which no canvas could withstand.
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EQUIVALENT SCALES in m/s
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Observational height corrections Typical
observational heights vary on different ships
from the first meters to several tens of meters.
On oil and drilling platforms observational
heights can approach 60-80 m. Corrections should
be applied using the same bulk parameterizations
which are expected to be used for the flux
computations.
Iteration scheme
Correction of winds, temperatures and humidity
according to the derived profiles
Coefficients and flux profile relationships for
uncorrected heights
Re-computation of the coefficients and fluxes
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Flux averaging and climatological
fields Averaging of the computed fluxes in the
space-time coordinates may suffer from the number
of observations (inadequate sampling).
gt500
lt5
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Nature of sampling bias in VOS fluxes time
dependent biases
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• Precipitation
• The use of conventional rain-collecting
  instruments, designed for land
• use, results in uncertainties which are of the
  same order of magnitude
• as the mean precipitation estimates.
• the effect of the flow around the ships overall
  structure which can lead to undercatch or
  overcatch depending on the location of gauge
• the effect of the flow in the close vicinity of
  the rain-gauge, which tends to carry the
  rainabove the orifice of the gauge and leads to a
  wind speed dependent undercatch.
• Parameterization of precipitation using the
  weather code information Tucker (1961), Dorman
  and Bourke (1978)

x1.85 mm, y5.66 mm, z8.13 mm (per 3 hours).