Scott Lindstrom University of WisconsinMadison CIMSS Cooperative Institute for Meteorological Satellite Studies Learning Objectives Subject Matter Experts What bands on ABI can detect foglow cloud formation and dissipation ID: 585180
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Slide1
Fog/Low Clouds: Formation and Dissipation
Scott
Lindstrom
University of Wisconsin-Madison CIMSS
(Cooperative Institute for Meteorological Satellite Studies
)Slide2
Learning Objectives
Subject Matter Experts
What bands on ABI can detect fog/low cloud formation and dissipationWhat GOES-R Products can detect fog/low cloud formation and dissipation
Michael PavolonisCorey Calvert
In this training, the acronym FLS means Fog/Low Stratus
BTD means Brightness Temperature DifferenceSlide3
Why create Probabilities of Flight Rules?
VFR - Visual flight rules
ceiling > 3000
ft and
vis
> 5 mi
MVFR - Marginal visual flight rules
1000
ft < ceiling < 3000 ft or 3 mi < vis < 5 miIFR - Instrument flight rules500 ft < ceiling < 1000 ft or 1 mi < vis < 3 miLIFR - Low instrument flight rulesceiling < 500 ft or vis < 1 mi
There
is no widely
accepted
definition of
Fog/Low
S
tratus (FLS) so
the GOES-R definition of FLS
relies on aviation flight
rules
The primary goal of the GOES-R fog/low cloud detection algorithm is to identify IFR, or lower, conditions.Slide4
Traditional GOES-East 11 – 3.9 μm BTD
FLS or Elevated
S
tratus?
BUT! It is difficult to differentiate between FLS or nonhazardous elevated stratus
clouds using the BTD product alone
This BTD product has been traditionally used in the past to detect nighttime FLS
(yellow/orange representing FLS)Slide5
Band differences can be related to surface- (or cloud-) based
emissivity differences or to sub-pixel effects
Regardless of cause, the differences can be exploitedSlide6
What can give information of low-level saturation below a cloud deck?
Surface Observations
Not always available
Not always representative
Clumsy to decodeModel Output
Provides information on low-level saturationIs the spatial resolution sufficient?
Is the model simulation correct?Slide7
Fused Fog/Low Cloud Detection Approach
Satellite Data
Statistical Model
Clear Sky
RTM
-Minimum channels needed: 0.65, 3.9, 6.7/7.3, 11, and 12/13.3
μm
-Previous image for temporal continuity (GEO only)
-Cloud PhaseIFR
and LIFR Probability
+
+
Static Ancillary Data
-DEM
-Surface Type
-Surface Emissivity
Daily SST Data
0.25 degree OISST
+
NWP
-Surface Temperature
-Profiles of T and
q
-RUC/RAP (2-3 hr forecast) or GFS (12 hr forecast)
NWP RH Profiles
-RUC/RAP (2-3 hr forecast) or GFS (12 hr forecast)
Other sources of relevant data (e.g.
sfc
obs
) influence results through the model fields
Total run time: 2 - 3 minutesSlide8
GOES-R Fields
MVFR Probability
LIFR Probability
Cloud Thickness
I
FR ProbabilitySlide9
The GOES-R FLS products were developed to improve upon the traditional FLS products.
The GOES-R products work day and night and provide information even when multiple cloud layers are present.Slide10
Fog Dissipation as a function of Cloud ThicknessSlide11
Cloud Thickness and Dissipation
1115 UTC GOES-R Cloud Thickness
Source
1415 UTC GOES-13 VisibleSlide12
Keep in mind…. (Model Domains)
Model used to predict location of FLS varies and there are inter-model seams
GOES-R FLS products can significantly change between neighboring pixels at model seams.
AK
Grid
(~11 km)
CONUS Grid
(~13 km)
Regional Grid
(~32 km)
GFSSlide13
Near the Equinoxes, around 3 - 7 UTC, 3.9
μm
stray light will greatly affect GOES BTD products
That effect can leak into the GOES-R FLS products – but it is mitigated in IFR Probability Products if the Rapid Refresh shows little saturation.
0415 UTC
0430 UTC
0445 UTC
Keep in mind…. (Stray Light)Slide14
GOES-R IFR Probabilities
GOES-R Cloud Thickness
Keep in mind…. (Day/Night)
Twilight Conditions:
Cloud Thickness not
computed
Still nighttime over here
Daytime Predictors
usedNighttime PredictorsusedNot shown on this slide: the Brightness Temperature Difference changes sign at sunrise as 3.9 μm radiation reflects/scatters off clouds. Changes in IFR Probability are more subtle than Brightness Temperature Difference changesSlide15
Precise information on dissipation: One-minute dataSlide16
GOES-R FLS Validation Over CONUS
The FLS products were validated using surface observations of ceiling and visibility
The plot below shows the Critical Success Index (CSI) of the daytime/nighttime GOES-R IFR probabilities along with the nighttime BTD product as a function of the threshold used to differentiate between FLS and non-FLS clouds
The maximum CSI
for the nighttime BTD product was calculated at
0.254
The maximum CSI for the daytime/nighttime IFR probabilities were calculated at 0.453/0.438 respectively, nearly double that of the traditional BTD product
The maximum CSI occurs when the IFR probability is ~25% (physical basis for our
colorbar
)Slide17
Summary
BTD
provides little information about
cloud ceilingslow clouds in regions of multiple cloud layersThe GOES-R IFR Probability fuses
satellite data with model information about low-level saturationSupplies information about cloud ceilingsFills in information in regions where multiple clouds layers exist
IFR Probability is a statistically superior product.Slide18
Internet Resources
Blog on IFR Probability fields
GOES-based fields available online
PowerPoint Presentation (from 2013) on IFR Probability