HIRS Observations of Clouds since 1978

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HIRS Observations of Clouds since 1978 Donald P.
Wylie W. Paul Menzel Cooperative Institute for
Meteorological Satellite Studies NOAA/NESDIS Unive
rsity of Wisconsin-Madison Madison,
Wisconsin,USA Darren Jackson Environmental
Technology Laboratory, NOAA/OAR Boulder,
Colorado, USA John Bates National Climate Data
Center Asheville, North Caroline USA CO2 Slicing
Method 22 year stats Effects of orbit drift, CO2
increase, and sensor changes 16 year
trends Comparison with ISCCP and GLAS October
2004
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Climate System Energy Balance
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Rationale for Cloud Investigations clouds are a
strong modulator of shortwave and longwave their
effect on global radiative processes is large
(1 change in global cloud cover equivalent to
about 4 change in CO2 concentration) accurate
determination of global cloud cover has been
elusive (semi transparent clouds often
underestimated by 10) global climate change
models need accurate estimation of cloud cover,
height, emissivity, thermodynamic state,
particle size (high/low clouds give
positive/negative feedback to greenhouse effect,
and higher albedo from anthropogenic
aerosols may be negative feedback) there is a
need for consistent long term observation records
to enable better characterization of weather and
climate variability (ISSCP is a good start)
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Why are clouds so tough?

• Aerosols lt0.1 micron, cloud systems gt1000 km
• Cloud particles grow in seconds climate is
  centuries
• Cloud growth can be explosive 1
  thunderstorm packs the energy of an H-bomb.
• Cloud properties can vary a factor of 1000 in
  hours.
• Few percent cloud changes drive climate
  sensitivity
• Best current climate models are 250 km scale
• Cloud updrafts are a 100 m to a few km.

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Cirrus detection has been elusive in the visible
bands
Depending on view angle GOES sees or misses Texas
cirrus
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IR window sees cirrus but cannot place height
correctly
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Radiance from a partly cloudy FOV
R1- N?Rclear air N? Ropq cld (Pc)
Two unknowns, N? and Pc , require two measurements
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CO2 slicing corrects for semi-transparency of
cirrus
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RTE in Cloudy Conditions I? ? Icd (1 - ?)
Iclr where cd cloud, clr clear, ? cloud
fraction ?
? o Iclr B?(Ts) ??(ps) ?
B?(T(p)) d?? . ?
ps
pc Icd (1-e?) B?(Ts) ??(ps)
(1-e?) ? B?(T(p)) d?? ?
ps o e? B?(T(pc)) ??(pc)
? B?(T(p)) d??
pc e? is emittance of cloud.
First two terms are from below cloud, third term
is cloud contribution, and fourth term is from
above cloud. After rearranging pc
dB? I? - I?clr ?e? ? ?(p)
dp . ps dp
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Cloud Properties from CO2 Slicing RTE for cloudy
conditions indicates dependence of cloud forcing
(observed minus clear sky radiance) on cloud
amount (???) and cloud top pressure (pc)
pc (I? - I?clr) ???
? ?? dB? .
ps Higher colder cloud or greater cloud amount
produces greater cloud forcing dense low cloud
can be confused for high thin cloud. Two
unknowns require two equations. pc can be
inferred from radiance measurements in two
spectral bands where cloud emissivity is the
same. ??? is derived from the infrared window,
once pc is known.
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CO2 channels see to different levels in the
atmosphere
14.2 um 13.9 um 13.6 um
13.3 um
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Different ratios reveal cloud properties at
different levels hi - 14.2/13.9 mid -
13.9/13.6 low - 13.6/13.3 Meas Calc
pc (I?1-I?1clr) ???1 ? ??1 dB?1
ps ----------- ----------------
pc (I?2-I?2clr) ???2 ? ??2 dB?2
ps
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Determining Cloud Presence and Properties Detect
clouds where (I? - I?clr) gt 1 mW/m2/ster/cm-1
in IRW or CO2 channels Use CO2 Slicing Method
to estimate pc pc selected best satisfies RTE
for all bands Estimate ??IRW using IRW
radiances If no CO2 bands qualify, IRW estimates
opaque cld pc If too low in atmosphere, declare
FOV clear
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Ratio of measured cloud signal for spectrally
close bands yields Pc
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UW NOAA Pathfinder HIRS global cloud statistics
from December 1978 through December 2001
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UW NOAA Pathfinder HIRS global cloud statistics
from December 1978 through December
2001 (corrected for higher cloud obstruction of
lower clouds using random overlap assumption)
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How Cloudy is the Earth?
CLAVR
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GLAS 22 Feb 28 Mar 2003, HIRS 1979 2001,
ISCCP 1983 2001, SAGE 1985-89, Surface Reports
1980-89, CLAVR 1982 - 2004 ISCCP reports 7-15
less cloud than HIRS because it misses thin
cirrus. HIRS and GLAS report nearly the same high
cloud frequencies. HIRS reports more clouds over
land than GLAS probably because GLAS sees holes
in low cumulus below the resolution of HIRS.
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GLAS
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All Cloud Observations from GLAS vs HIRS
GLAS
HIRS
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HIRS minus GLAS All Cloud Difference
HIRS Frequency of All Clouds during the period of
GLAS
GLAS finds more tropical clouds over oceans where
HIRS reports lt40. GLAS finds less clouds in
polar regions and western tropical Pacific.
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HIRS minus GLAS High Cloud Difference
HIRS Frequency of High Cloud
HIRS GLAS Difference
GLAS gt HIRS HIRS gt GLAS
HIRS reports more high clouds in parts of tropics
and southern hemisphere, but areas of differences
are scattered and not meteorologically organized.
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Looking at animation of monthly means for 1997
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HIRS-GLAS by latitude
HIRS under detection is mainly over oceans.
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Inferring Decadal HIRS Cloud Trends requires
corrections for (1) anomalous satellite data or
gaps (2) orbit drift (3) CO2 increase
constant CO2 concentration was assumed in
analysis
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Satellite by satellite analysis Gap in 8am/pm
orbit coverage between NOAA-8 and -10 HIRS cloud
trends show unexplained dip with NOAA-7 in 2
am/pm orbit.
Used only 2 am/pm orbit data after 1985 in cloud
trend analysis for continuity of data and
satellite to satellite consistency
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Measurements from 9 sensors used in 22 year study
of clouds
morning (8 am LST) afternoon (2 pm LST) NOAA 6
HIRS/2 NOAA 5 HIRS NOAA 8 HIRS/2 NOAA 7
HIRS/2 NOAA 10 HIRS/2 NOAA 9 HIRS/2 NOAA 12
HIRS/2 NOAA 11 HIRS/2I NOAA 14 HIRS/2I
HIRS/2I ch 10 at 12.5 um instead of prior
HIRS/2 8.6 um. Asterisk indicates orbit
drift from 14 UTC to 18 UTC over 5 years of
operation
Some sensors experienced significant orbit drift
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all 2 am/pm satellites adjusted linearly to
represent data for ascending node at 1400 hrs
local time
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Atmospheric CO2 has not been constant
(From Engelen et al., Geophys Res Lett, 2001)
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SARTA calculations BT with 360 ppmv minus BT
with 340,345,380 ppmv
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HIRS cloud trends have been calculated with CO2
concentration assumed constant at 380 ppm.
Lower CO2 concentrations increase the
atmospheric transmission, so radiation is
detected from lower altitudes in the atmosphere.
For January and June 2001 the clouds detected
by NOAA 14 in the more transparent atmosphere
(CO2 at 335 ppm) are found to be lower by 13-50
hPa ?dry(335,p,ch) ?dry(380,p,ch)335/380)
?(p,ch) ?dry(p,ch)?H2O(p,ch)?O3(p,ch).
More transparent atmosphere (CO2 at 335 ppm)
results in HIRS reporting clouds lower by 15-50
hPa with 2 less high clouds than in the more
opaque atmosphere (CO2 at 380 ppm) this implies
that the frequency of high cloud detection in the
early 1980s should be adjusted down. Cloud time
series was adjusted to represent a linear
increase of CO2 from 335 ppm in 1979 to 375 ppm
in 2001
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Wielicki et al (2002) CERES deviation of
reflected shortwave flux wrt 1985-89 mean for
20N-20S
4 2 0 -2
HIRS deviation of hi cloud detection wrt 1978-88
mean
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• Conclusions
• clouds were found in 75 of HIRS observations
  since 1978
• (hi clouds in 33)
• good agreement with GLAS
• ISCCP finds 10-15 fewer high and all clouds
• loop of monthly means shows latitudinal cloud
  cover follows the sun
• 16 yr trends in HIRS high cloud statistics
  reveal modest 2 increase
• during last decade compared with previous decade
• orbit drift, CO2 increase, and satellite to
  satellite differences were mitigated
• ISCCP shows decreasing trends in total cloud
  cover of 3 to
• 4 per decade but little high cloud trend