1.2
Recent Satellite Studies
D. H. JOHNSON
During the past decade the global networks of meteorological observations have been
richly supplemented by a growing wealth of satellite data. Amongst the quantities of
interest to meteorologists or oceanographers, measured or derived from satellite observations over the oceans are: cloud amount and type; reflected short wave radiation and
albedo; total outgoing long-wave radiation; long-wave radiation in selected wave bands;
the radiation balance of the earth-atmosphere system; temperature and height of cloud
tops; sea surface temperature; atmospheric vertical temperature profile; atmospheric
water vapour content; low-level wind speeds; winds at cloud levels; the fields of divergence and vorticity of the air flow; the sea state; and the extent of sea ice. In addition
there are proposals for the future measurement of chlorophyll and plankton population
by spectrometry .
For some of these quantities the work so far undertaken and described has been
concerned mainly to establish the feasibility of the instrumental technique or method of
analysis. For others the global climatology has been studied and in these the Indian Ocean
area is naturally included. As yet, very few investigations have dealt specifically with
Indian Ocean problems. A useful review of basic techniques and of the data which are
available or will soon be available for study from United States sources has been provided
by LEESE, BOOTH and GODSHALL (1970). One omission in the last paper is reference to
the recent work on the deduction of sea states and surface wind conditions from sun-glint
patterns (STRONG and RUFF, 1970).
I. Radiation Measurements
Studies of the earth's radiation budget, using global observations made with low
resolution radiometers carried by the TIROS and ESSA satellites have confirmed, not
surprisingly, that the earth-atmosphere system is in near radiative equilibrium. The outgoing long-wave radiation measured from satellites has a latitudinal variation which
follows closely that obtained from presatellite computations with magnitudes, as reported
by VONDER HAAR and SUOMI (1969) generally higher than, but within 5% of those
computed in the earlier studies. The mean annual planetary albedo has been computed
by the latter authors from the satellite data to be 29%, but they point out that the values
measured for the tropics are much lower than was earlier assumed. It appears that the
observations of clouds made from the surface by tropical observers probably overestimate
the opaque cloud cover, and it must be concluded that about 30% more energy is absorbed
by the earth-atmosphere system in the tropics than was previously supposed. As a result,
previous estimates of poleward heat transport must also be increased. The question
remaining is whether the increased transports take place primarily in the air or the sea.
Recent Satellite Studies
D. H. JOHNSON
During the past decade the global networks of meteorological observations have been
richly supplemented by a growing wealth of satellite data. Amongst the quantities of
interest to meteorologists or oceanographers, measured or derived from satellite observations over the oceans are: cloud amount and type; reflected short wave radiation and
albedo; total outgoing long-wave radiation; long-wave radiation in selected wave bands;
the radiation balance of the earth-atmosphere system; temperature and height of cloud
tops; sea surface temperature; atmospheric vertical temperature profile; atmospheric
water vapour content; low-level wind speeds; winds at cloud levels; the fields of divergence and vorticity of the air flow; the sea state; and the extent of sea ice. In addition
there are proposals for the future measurement of chlorophyll and plankton population
by spectrometry .
For some of these quantities the work so far undertaken and described has been
concerned mainly to establish the feasibility of the instrumental technique or method of
analysis. For others the global climatology has been studied and in these the Indian Ocean
area is naturally included. As yet, very few investigations have dealt specifically with
Indian Ocean problems. A useful review of basic techniques and of the data which are
available or will soon be available for study from United States sources has been provided
by LEESE, BOOTH and GODSHALL (1970). One omission in the last paper is reference to
the recent work on the deduction of sea states and surface wind conditions from sun-glint
patterns (STRONG and RUFF, 1970).
I. Radiation Measurements
Studies of the earth's radiation budget, using global observations made with low
resolution radiometers carried by the TIROS and ESSA satellites have confirmed, not
surprisingly, that the earth-atmosphere system is in near radiative equilibrium. The outgoing long-wave radiation measured from satellites has a latitudinal variation which
follows closely that obtained from presatellite computations with magnitudes, as reported
by VONDER HAAR and SUOMI (1969) generally higher than, but within 5% of those
computed in the earlier studies. The mean annual planetary albedo has been computed
by the latter authors from the satellite data to be 29%, but they point out that the values
measured for the tropics are much lower than was earlier assumed. It appears that the
observations of clouds made from the surface by tropical observers probably overestimate
the opaque cloud cover, and it must be concluded that about 30% more energy is absorbed
by the earth-atmosphere system in the tropics than was previously supposed. As a result,
previous estimates of poleward heat transport must also be increased. The question
remaining is whether the increased transports take place primarily in the air or the sea.