wv imagery analysis related to pv concept wv imagery analysis related to pv concept wv imagery...
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WV imagery analysis related to PV concept WV imagery analysis related to PV concept
WV imagery features related to synoptic dynamical WV imagery features related to synoptic dynamical structuresstructures
PART IIPART IIInterpretation of 6.2Interpretation of 6.2 m m channel radiance in image format channel radiance in image format
INTERPRETATION GUIDE TO MSG INTERPRETATION GUIDE TO MSG WATER VAPOUR CHANNELSWATER VAPOUR CHANNELS
Christo GeorgievNational Institute of Meteorology
& Hydrology, Bulgaria
Patrick SanturetteMétéo-France
Acknowledgments
The Interpretation Guide to MSG WV Channels is developed by Christo Georgiev and Patrick Santurette through the Water Vapour Imagery Project of the bilateral cooperation between Météo-France and the National Institute of Meteorology and Hydrology of Bulgaria.
The illustrations made by using satellite imagery from Meteosat satellites of EUMETSAT, other observational data and numerical model fields are the property of Météo-France, which has funded the work on the manual.
This training tool is submitted to EUMETSAT as a contribution of France and Bulgaria to the MSG Interpretation Guide.
Chapter 4 of the book is unique in bringing together the interpretation of • water vapor images, • potential vorticity fields and • model diagnostics
as a guide to validating numerical model analyses or
short period forecasts.
Published by Academic PressCopyright © 2005, Elsevier Inc.
More information is available at:http://books.elsevier.com/earthscience/
The Interpretation Guide to MSG WV Channels is drawn on brief
excerpts from Chapters 1-3 and Appendix A of the book:
Patrick Santurette, Météo-France
Christo Georgiev, NIMH, Bulgaria
WV WV Imagery Analysis Imagery Analysis
Many pixels are considered as patterns and features of grey shades.
The interpretation is aimed to relate the patterns of different moisture distribution and their changes with time to specific atmospheric circulation systems and processes.
WV channelWV channel radiance in radiance in image formatimage format
• Of the two MSG WV channels, the radiation in 6.2
m band is more highly absorbed by water
vapour and, being presented in image format, it
better reflects moisture content of the
troposphere.
• Therefore, the 6.2 m radiation measurements
are the most relevant of the WV channels to be
displayed and used in image format.
Operational use of WV imageryOperational use of WV imagery
• The WV channel radiance in 6.2 m of MSG (6.3
m of Meteosat 1-7) is closely correlated with
humidity field in the layer between 600 and 300
hPa and provides information on the flow
patterns at middle and upper troposphere.
• Therefore, WV imagery may serve as a tool for
operational synoptic scale analysis.
Association of light and dark imagery Association of light and dark imagery featuresfeatures to to dynamical dynamical structuresstructures
• On a water vapour (WV) image being displayed in grey shades, the areas of dry upper-troposphere appear darker, and the areas of higher moisture content appear lighter.
• The basis for synoptic scale applications of WV imagery is that moist and dry regions as well as the boundaries between them often relate to significant upper-level flow features such as troughs, deformation zones and jet streams.
DYNAMIC APPROACH FOR WV DYNAMIC APPROACH FOR WV IMAGERY INTERPRETATIONIMAGERY INTERPRETATION
• An useful approach is interpreting satellite
imagery jointly with various dynamical fields
for the purposes of operational forecasting.
• In order to perform dynamic water vapour
imagery analysis, it calls for applying relevant
dynamical concepts.
WATER VAPOUR IMAGERY WATER VAPOUR IMAGERY
ANALYSISANALYSIS
WATER VAPOUR IMAGERY ANALYSIS WATER VAPOUR IMAGERY ANALYSIS RELATED TO PV CONCEPTRELATED TO PV CONCEPT
A simple isentropic coordinate version of PVA simple isentropic coordinate version of PV
a-1 PV , where:
1 θp - g - is the air mass density in xy space
potential temperature, p pressure, g is the acceleration due to the gravity.
fais the absolute isentropic vorticity
Potential vorticity is a product of the absolute vorticity and the static stability.
UNITSUNITS for presentation of PV for presentation of PV
10-6 m2 s-1 K kg-1 ‘PV-unit’ (PVU)
• Potential vorticity is an effective dynamical parameter for studying the appearance and evolution of dynamical structures at synoptic scale due to the following important properties:
• Conservation for adiabatic frictionless motions, and
• Specific climate distribution in the atmosphere
CONSERVATION PRINCIPLE FORCONSERVATION PRINCIPLE FOR PV PV
If one neglects diabatic and turbulent mixing processes, PV of an air parcel remains preserved along it’s 3-D trajectory of motion
• When the distance h increases (decreasing
of the gradient), the vorticity increases• Conversely, when h decreases (increasing
of the gradient), the vorticity decreases.
A vorticity tube between constant (iso-) surfaces
CLIMATE DISTRIBUTION OFCLIMATE DISTRIBUTION OF PV PV
In the middle and upper troposphere
PV is ranging from
0.5 to 1 PVU
PV discontinuity around the tropopause and its conservation property allows us to define the surface of constant PV = 1.5 PVU as the “dynamical tropopause” separating the troposphere with weak PV, from the stratosphere with its strong PV.
In the stratosphere PV > 3 PVU ,
due to the strong increase of the static
stability. 65°N 25°N LATITUDE
dynamical tropopause
A PositiveA Positive PV anomaly PV anomaly at at upper-level upper-levelss anandd associated associated synopticsynoptic development development
PV anomaly = > 1.5 PVU
In a baroclinic flow increasing with height, the intrusion of PV anomaly in the troposphere produces vertical motion: the deformation of the iso- imposes ascending motion ahead of the anomaly and subsiding motion behind the anomaly.
A PV anomaly is produced by a stratospheric intrusion in the upper troposphere. Due to the PV conservation, the anomaly leads to deformations in and vorticity of the surrounding air - potential temperature
TROPOPAUSE DYNAMIC ANOMALYTROPOPAUSE DYNAMIC ANOMALY
An upper level PV anomaly, advected down to middle troposphere corresponds to an area of the 1.5 PVU surface moving down to mid- or low levels. Such a low tropopause area (moving in a baroclinic environment) is referred to as a “tropopause dynamic anomaly”.
TROPAPUSE TROPAPUSE DYNAMIC DYNAMIC ANOMALYANOMALY
6.2 m image & 1.5 PVU surface heights 1.5 PVU surface heights
A tropopause dynamic anomaly exhibits:• a local minimum of the 1.5 PVU surface height;• descending motions in upper and middle troposphere;• dark grey shades of the WV image.
TROPOPAUSE DYNAMIC ANOMALY (Example 1/2)TROPOPAUSE DYNAMIC ANOMALY (Example 1/2)
Forward to a tropopause dynamic anomaly these are present:• a local maximum of the 1.5 PVU surface height;• ascending motion in upper and middle troposphere;• light grey shades of the WV image.
6.2 m image & 1.5 PVU surface heights 1.5 PVU surface heights
TROPOPAUSE DYNAMIC ANOMALY (Example 2/2)TROPOPAUSE DYNAMIC ANOMALY (Example 2/2)
Relationship betweenRelationship between WV image dark/light shades WV image dark/light shades and low/high geopotential of the and low/high geopotential of the 1.5 PVU surface1.5 PVU surface
WV imagery is a tool for upper-level diagnosis.
Efficient approaches for imagery analysis in
forecasting environment are:
• Superimposing WV images on upper level
dynamical fields, derived by NWP models, e.g.
1.5 PVU surface heights; 300 hPa wind field.
• Imagery interpretation with reference to
• Vertical cross-sections of NWP model-
derived PV and relative humidity.
• Observational data derived by upper-air
soundings.
OPERATIONAL TOOLSOPERATIONAL TOOLS
DynamicDynamic WV WV imagery analysis imagery analysis
6.2 m water vapour image
Dynamic interpretation
of WV imagery is
efficient to be
performed in areas of
high contrast between
light and dark image
grey shades that is
produced by
significant large-scale
dynamical processes.
WVWV imagery and imagery and mid/upper level dynamical fieldsmid/upper level dynamical fields
6.2 m image & 1.5 PVU surface heights 1.5 PVU surface heights
• Low tropopause
heights are correlated
with the dark zones in
the imagery.• High geopotential of
the 1.5 PVU surface
are associated with
light grey shades.
Areas of sharp image
grey shade contrast
are associated with
zones of strong height
gradient of the
dynamical tropopause.
WVWV imagery and imagery and mid/upper level dynamical fieldsmid/upper level dynamical fields
1.5 PVU surface heights 1.5 PVU surface heights // wind at 300 hPawind at 300 hPa (only > 100 kt)(only > 100 kt)
A sharp boundary
between different
moisture or cloud
regime on the WV
image is and area of
strong gradient of the
dynamical tropopause
heights.
This boundary is also
aligned with the zone
of the highest upper
level wind speed.
WVWV imagery and imagery and mid/upper level dynamical fieldsmid/upper level dynamical fields
Contours of wind speed > 100 ktContours of wind speed > 100 kt // wind > 80 kt at 300 hPawind > 80 kt at 300 hPa
Generally, there is
well defined jet
stream axes nearly
coincident with the
moisture boundaries
oriented southwest-
northeast.
The jet axis of the
maximum wind speed
is likely along the
most contrast part of
moisture boundary in
the WV image.
6.2 m
A synoptic-scale dark zone on the 6.2 m channel image is consistent with low geopotential of the dynamical tropopause (1.5 PVU surface, solid cross-section contour).
6.2 m image & 1.5 PVU surface height1.5 PVU surface heightCross-section of PVCross-section of PV
WVWV imagery and imagery and vertical cross-sectionsvertical cross-sections
Tropopause dynamic anomaliesTropopause dynamic anomalies
A tropopause dynamic anomaly is associated with intrusion of very dry stratospheric air down to middle troposphere along the zone of tropopause folding.
PV (brown)PV (brown)Relative Relative humidity (red)humidity (red)
Cross-section ofCross-section of
Tropopause dynamic anomaliesTropopause dynamic anomalies
The strip of nearly black WV image gray shades is produced by very dry air of less than 10% relative humidity at mid- to upper troposphere along the zone of a tropopause folding.
6.2 m WV imageWV image Cross-section of Relative humidityCross-section of Relative humidity
500 hPa
WVWV imagery and imagery and upper air soundingsupper air soundings
Three upper air soundings around the WV dark strip reveal decreasing of upper-level moisture in the direction of tropopause folding, as seen by the darkening in the WV image.
TD T TD T TTD
T – air temperatureTD – dewpoint
PV conceptPV concept and and upper air soundingsupper air soundings
The tropopause level derived by using temperature lapse rate is not correct with references to the wind field and WV image interpretation in terms of PV concept.
6.2 m image, 1.5 PVU heights1.5 PVU heights
Tropopause by lapse rate
TD T
PV conceptPV concept and and upper air soundingsupper air soundings6.2 m image, 1.5 PVU heights1.5 PVU heights
Above the sounding release point: High gradient of 1.5 PVU surface heights WV image dark zone Dynamical tropopause at 600 hPa analysed by the NWP model.
Tropopause by lapse rate
Dynamical Tropopause
TD T
PV conceptPV concept and and upper air soundingsupper air soundings
Cross-section of PVCross-section of PV
Up
per
-air
so
und
ing
When raising through the tropopause folding, the radio-sound reported strong wind sheer from north-easterly at 500 hPa to south-westerly flow at 300 hPa, divided by a zone of low-speed winds.
TD T
PV conceptPV concept and and upper air soundingsupper air soundings
300 hPa wind 300 hPa wind (blue)(blue)
500 hPa wind 500 hPa wind (yellow)(yellow)
Upper-air Upper-air sounding sounding release pointrelease point
Accordingly, the numerical model has analysed south-easterly wind at 500 hPa (yellow arrows) and south-westerly flow at 300 hPa (blue arrows) , as being reported by the upper-air sounding.
WV image WV image && 1.5 PVU surface height1.5 PVU surface height Cross-section of PVCross-section of PV
WVWV imagery and imagery and PV conceptPV concept
The 6.2 m channel imagery when interpreted in terms of PV concept is a powerful operational tool for upper-level diagnosis, due to the ability for easily detecting tropopause foldings.
SuperimposingSuperimposing WVWV image imagess on on mid- and mid- and upper level dynamical fieldsupper level dynamical fields
1.5 PVU surface heights 1.5 PVU surface heights andand wind at 300 hPawind at 300 hPa
•The jet axis closely mirrors the shape of the maximum radiance
contrast in the water vapour image. •The strong gradient of the dynamical tropopause height follows
the jet and the dark/light contrast in the image.
JET STREAM
JET STREAMAreas of low tropopause (1.5 PVU surface) height are associated with positive PV anomalies, and they are well correlated with the dark zones in the imagery.
WATER VAPOUR IMAGERY WATER VAPOUR IMAGERY
ANALYSISANALYSIS
WV IMAGERY FEATURES RELATED TO WV IMAGERY FEATURES RELATED TO SYNOPTIC DINAMICAL STRUCTURESSYNOPTIC DINAMICAL STRUCTURES
Radiance in 6.2 m channel is related to the synoptic-scale motion field above 600 hPa and thus it is sensitive to the following upper level dynamical features:
Upper level jet Upper level PV (dynamic tropopause) anomalySynoptic vertical motion
areas of ascending air = white zones areas of subsiding air = dark zones
upper level PV / dynamic tropopause anomaly = dark zones
jet streak / strong gradient of 1.5 PVU surface heights = strong humidity gradient in the imagery (dry air on polar side)
WVWV CHANNEL RADIANCE CHANNEL RADIANCERELATED TO UPPER-LEVEL DYNAMICSRELATED TO UPPER-LEVEL DYNAMICS
PV – WV image RELATIONSHIPPV – WV image RELATIONSHIP UPPER-LEVEL DYNAMICAL PERSPECTIVEUPPER-LEVEL DYNAMICAL PERSPECTIVE
1.5 PVU surface heights 1.5 PVU surface heights // wind at 300 hPa (only > 70 kt)wind at 300 hPa (only > 70 kt)
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
• Being upper-level dynamical structures, the jet systems are related to characteristic cloud and moisture regimes that are well seen in the WV imagery.
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
• The jet streams are important dynamical features of the synoptic scale circulation.
• One of the most efficient use of WV imagery for weather forecasting is to observe the structure and evolution of the jet stream zones in association with the dynamical tropopause behaviour by applying the PV concept.
• Changes in the jet stream and the height of the dynamical tropopause may be considered to predict time changes in the related circulation systems and may provide early indication of NWP model validity.
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
Wind at 300 hPaWind at 300 hPa (only > 100 kt)(only > 100 kt)Typically, on a WV
image, there are
many well defined
boundary features,
and only some of
them are associated
with jet stream axes.
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
Typically, on a WV
image, there are
many well defined
boundary features,
and only some of
them are associated
with jet stream axes.
1.5 PVU surface heights1.5 PVU surface heights
The jet stream axes are present along the boundaries of different
moisture regimes produced by significant tropopause sloping that is
indicated by strong gradient in geopotential of the 1.5 PVU surface.
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
1.5 PVU surface heights1.5 PVU surface heights
The jet stream
system with a high
amplitude upper-level
through consists of
two branches.
• A jet stream branch
coming from the
upstream ridge.
• A jet stream branch
on the forward side
of the through.
Wind-speed at 300 hPa (only > 100 kt)Wind-speed at 300 hPa (only > 100 kt)
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
The axes of
maximum speed of
the two jet stream
branches
are extended along
cloud boundaries or
along moisture
boundaries.
Wind-speed at 300 hPa (only > 100 kt)Wind-speed at 300 hPa (only > 100 kt)
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
The axis of a jet
stream branch
coming from the
upstream ridge
is parallel to the
moisture boundary,
located to the east.
Wind-speed at 300 hPa (only > 100 kt)Wind-speed at 300 hPa (only > 100 kt)
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
The jet stream axis
on the forward
through side is more
distinct on the WV
image, and
The jet axis is usually
coincident with
moisture boundaries.
The jet streak appears at the cloud boundary, where such a cloud
boundary is in line along with the moisture boundary.
when such a cirrus boundary is aligned parallel to the moisture
boundary (Ci are colored in cyancyan colour) .
Due to difficulties in distinguishing cloud boundaries in WV imagery grey shades, the jet stream features are better seen in a colour image palette.
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
Wind-speed at 300 hPa (only > 90 kt)Wind-speed at 300 hPa (only > 90 kt)
The axis of the jet
stream branch from
the upstream ridge is
likely to be present
along the boundary
of cirrus clouds,
Ci
6.2 m
At the convex segment
of the jet stream
feature on the forward
side of the through, the
jet axis is present close
to the cirrus boundary,
when this boundary is
aligned with a moisture
boundary.
the jet axis is often coincident with boundaries between different
moisture regimes.
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
Wind-speed at 300 hPa (only > 90 kt)Wind-speed at 300 hPa (only > 90 kt)
At the poleward and
the equatorward
segments of the
feature,
6.2 m
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
Wind-speed at 300 hPa (only > 90 kt)Wind-speed at 300 hPa (only > 90 kt)
Wind speedWind speed
Relative HumidityRelative Humidity
Vertical cross-sectionsVertical cross-sections
Dynamical structure of the jet stream zone in the view of the PV concept may well be seen in the
The moisture/upper-level cloud boundary coincides with the maximum wind speed
6.2 m
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
Wind-speed at 300 hPa (only > 90 kt)Wind-speed at 300 hPa (only > 90 kt)The intrusion into the troposphere of dry stratospheric air
Potential VorticityPotential Vorticity
warm
Relative HumidityRelative Humidity
with high PV produces warm brightness temperatures of the WV image
6.2 m
JET-STREAM RELATED PATERNSJET-STREAM RELATED PATERNS
Wind-speed at 300 hPa (only > 90 kt)Wind-speed at 300 hPa (only > 90 kt)
The position of the maximum wind-speed contour coincides with the zone of folding of the tropopause (1.5 PVU constant surface).
Potential VorticityPotential Vorticity
Wind speedWind speed
Therefore, being in the position of a jet stream the PV anomaly is in a dynamic phase of interaction with the jet.
6.2 m
Upper PV anomaly in a dynamical phase:Upper PV anomaly in a dynamical phase:
Interaction between tropopause anomaly and the jet stream « forcing» of a jet-streak
vertical motion
tropopause anomaly,tropopause anomaly, vertical motionvertical motionjet-streak,jet-streak,
IINTERACTION OF THE JET STREAM WITH NTERACTION OF THE JET STREAM WITH A TROPOPAUSE DYNAMIC ANOMALYA TROPOPAUSE DYNAMIC ANOMALY
WV imagery is a tool for observing tropopause dynamic anomalies and jet streams in the context of their interaction, which is critical for the evolution of the synoptic situation.
Interaction of a jet-stream with a tropopause dynamic anomalyInteraction of a jet-stream with a tropopause dynamic anomaly::A jet-streak appears in the southern part of the anomaly (red arrows), associated with strong tropopause heights gradient
JET- STEAK
WV image darkzone
Tropopause dynamic anomaly
JJet-streaet-streakk As seen in the WV image
Wind-speed at 300 hPa (only > 80 kt)Wind-speed at 300 hPa (only > 80 kt)
Jet-streak
CYCLOGENESISCYCLOGENESIS
• WV imagery is an operational tool for studying the cyclogenesis, from the very beginning of the process (about 24 to 48 hours before the onset of surface deepening) to the decay of the low system, as well as during any periods of reinforcement.
Cyclogenesis development : Cyclogenesis development : conceptual schema in satellite imagery conceptual schema in satellite imagery
• Before the onset of cyclogenesis, the low level (blue arrow in the cold air and orange in the warm air) and upper level (brown arrow) flows are in the same direction.
• There is no clear organisation of the cloud mass; the clouds associated to the moist warm air are broken and scattered in several layers.
• As the low deepening: at the lowest part of the cloud mass this organises a flow with a direction different from the upper level flow.
• North of the low, the upward flow drags low and medium clouds around the low centre in a direction perpendicular to that of the highest clouds: a cloud head with a cusp or hook shape appears.
• At the same time, the subsiding cold flow enters the south of the low (dry intrusion; dark to light blue arrow), while the upstream cold air is recaptured north of the low by the northerly flow (light blue broken arrow).
Cyclogenesis development : Cyclogenesis development : conceptual schema in satellite imagery conceptual schema in satellite imagery
CYCLOGENESISCYCLOGENESIS
• WV imagery is a useful operational tool for interpretation the following different aspects concerning cyclogenesis:
• Cyclogenesis with upper-level precursors.
• Dry intrusion as an ingredient and a precursor of cyclogenesis.
• Dry intrusion related to kata- and ana-cold fronts.
CYCLOGENESIS WITH CYCLOGENESIS WITH UPPER-LEVEL PRECURSORUPPER-LEVEL PRECURSOR
• Deep tropospheric cyclogenesis is a result of a baroclinic interaction between a tropopause dynamic anomaly and a jet-stream in upper level as well as a low-level baroclinic zone.
• The crucial elements leading to such a cyclogenesis with an upper level precursor are observed by means of synoptic and WV imagery analyses.
UPPER-LEVEL PRECURSOR OF UPPER-LEVEL PRECURSOR OF CYCLOGENESISCYCLOGENESIS
An upper level precursor of deep tropospheric cyclogenesis is a clear isolated tropopause dynamic anomaly at an initial phase that is seen as a dry feature in the WV imagery.
specific dark WV imagery feature
1.5 PVU heights1.5 PVU heights
Cyclogenesis with upper-level precursorCyclogenesis with upper-level precursorWV imagery analysis
A PV anomaly, visible on the WV image as a dry zone, corresponding to a minimum of the 1.5 PVU surface height.
tropopause dynamic anomaly
WV imagery analysis
The upper-level forcing at a very initial phase of cyclogenesis is evident in the superposition of the WV image and dynamical fields.
Cyclogenesis with upper-level precursorCyclogenesis with upper-level precursor
The moist white zone ‘C’ associated with relatively high tropopause height is the sign of ascending motion downstream the tropopause dynamic anomaly.
WV imagery analysis
The baroclinic zone at location ‘B’ is marked by a good relation between the jet axis (the most inner blue contour), the strong gradient of 1.5 PVU heights (red contours), and the strong humidity gradient in WV image dark / white shades.
Cyclogenesis with upper-level precursorCyclogenesis with upper-level precursor
tropopause dynamic anomaly
The cyclogenesis occurs as a result of interaction between the tropopause dynamic anomaly and the baroclinic zone. The WV images show the main features at the beginning of the interaction and during the development phase after 24 hours.
WV imagery analysis17 February 1997 1200 UTC
18 February 1997 1200 UTC
Cyclogenesis with upper-level precursorCyclogenesis with upper-level precursor
The dark spot associated with the tropopause dynamic anomaly (at the green arrow) approaches the white band ‘B’ , which corresponds to the baroclinic zone, and then interacts with it.
WV imagery analysis17 February 1997 1200 UTC
Cyclogenesis with upper-level precursorCyclogenesis with upper-level precursor
In the same time, the white band ‘B’ undulates, taking an appearance of a baroclinic leaf, and becomes clearest as it is approached by the white zone ‘C’, originally associated with the tropopause dynamic anomaly.
WV imagery analysis17 February 1997 1200 UTC
Cyclogenesis with upper-level precursorCyclogenesis with upper-level precursor
BAROCLINIC LEAF
BAROCLINIC LEAF
During the development phase the two white features ‘B’ and ‘C’ merge, contributing to formation of a cloud head ‘H’ to the north of cyclogenesis area. The dry spot, associated with the PV anomaly develops as a dry intrusion to the south-west.
WV imagery analysis17 February 1997 1200 UTC
18 February 1997 1200 UTC
Cyclogenesis with upper-level precursorCyclogenesis with upper-level precursor
CLOUD HEAD
CLOUD HEADDRY INTRUSION
DRY INTRUSION
DRY SPOT
DRY SPOT
WV imagery patterns ofWV imagery patterns of cyclone cyclone dynamicsdynamics
A : tropopause anomaly as a precursor of cyclogenesis
B : baroclinic zone as seen in moist ascent
P : cloud head
I : dry intrusion
WV imagery patterns ofWV imagery patterns of cyclone cyclone dynamicsdynamics
A : tropopause anomaly as a precursor of cyclogenesis
B : baroclinic zone as seen in moist ascent
P : cloud head
I : dry intrusion
WV imagery patterns ofWV imagery patterns of cyclone cyclone dynamicsdynamics
A : tropopause anomaly as a precursor of cyclogenesis
B : baroclinic zone as seen in moist ascent
P : cloud head
I : dry intrusion
WV imagery patterns ofWV imagery patterns of cyclone cyclone dynamicsdynamics
A : tropopause anomaly as a precursor of cyclogenesis
B : baroclinic zone as seen in moist ascent
P : cloud head
I : dry intrusion
WV imagery patterns ofWV imagery patterns of cyclone cyclone dynamicsdynamics
A : tropopause anomaly as a precursor of cyclogenesis
B : baroclinic zone as seen in moist ascent
P : cloud head
I : dry intrusion
WV imagery patterns ofWV imagery patterns of cyclone cyclone dynamicsdynamics
A : tropopause anomaly as a precursor of cyclogenesis
B : baroclinic zone as seen in moist ascent
P : cloud head
I : dry intrusion
WV imagery patterns ofWV imagery patterns of cyclone cyclone dynamicsdynamics
A : tropopause anomaly as a precursor of cyclogenesis
B : baroclinic zone as seen in moist ascent
P : cloud head
I : dry intrusion
WV imagery patterns ofWV imagery patterns of cyclone cyclone dynamicsdynamics
A : tropopause anomaly as a precursor of cyclogenesis
B : baroclinic zone as seen in moist ascent
P : cloud head
I : dry intrusion
WV imagery patterns ofWV imagery patterns of cyclone cyclone dynamicsdynamics
A : tropopause anomaly as a precursor of cyclogenesis
B : baroclinic zone as seen in moist ascent
P : cloud head
I : dry intrusion
• Moist ascent at the baroclinic zone
• Cloud-head
• Dry intrusion
• Kata- and ana-cold fronts
WV IMAGERY PATTERNS OF WV IMAGERY PATTERNS OF CYCLONECYCLONE DYNAMICSDYNAMICS
DRY SPOT and DRY INTRUSIONDRY SPOT and DRY INTRUSION
• Deep tropospheric cyclogenesis is associated with a dry spot on the WV imagery as an upper level precursor.
• Dry intrusion appears in the leading zone of the dry spot when cyclogenesis develops.
as characteristic WV imagery patterns of the as characteristic WV imagery patterns of the upper-level dynamics of cyclogenesisupper-level dynamics of cyclogenesis
22ndnd 1999 Christmas storm over France 1999 Christmas storm over France
Undulation of the baroclinic zone
Polar jet stream
Tropopause anomaly
WV
characteristic WV imagery patterns of characteristic WV imagery patterns of upper-level dynamics of cyclogenesisupper-level dynamics of cyclogenesis
Ingredients of Ingredients of cyclogenesiscyclogenesis
Undulation of the baroclinic zone
Polar jet stream
Tropopause anomaly
Z 1.5 PVU
’w 850 hPa
Jet
Pmer
Analyse ARPEGE
WV
22ndnd 1999 Christmas storm over France 1999 Christmas storm over France
characteristic WV imagery patterns of characteristic WV imagery patterns of upper-level dynamics of cyclogenesisupper-level dynamics of cyclogenesis
Ingredients of Ingredients of cyclogenesiscyclogenesis
Strengthening of undulation and ascending at the baroclinic zone
Appearance of a «cloud-head»
WV
22ndnd 1999 Christmas storm over France 1999 Christmas storm over France
characteristic WV imagery patterns of characteristic WV imagery patterns of upper-level dynamics of cyclogenesisupper-level dynamics of cyclogenesis
Dry Intrusion
WV
22ndnd 1999 Christmas storm over France 1999 Christmas storm over France
characteristic WV imagery patterns of characteristic WV imagery patterns of upper-level dynamics of cyclogenesisupper-level dynamics of cyclogenesis
Dry slot
WV
22ndnd 1999 Christmas storm over France 1999 Christmas storm over France
characteristic WV imagery patterns of characteristic WV imagery patterns of upper-level dynamics of cyclogenesisupper-level dynamics of cyclogenesis
DRY SPOT, DRY INTRUSION and DRY SLOT: DRY SPOT, DRY INTRUSION and DRY SLOT:
characteristic WV imagery patterns of characteristic WV imagery patterns of upper-level dynamics of cyclogenesisupper-level dynamics of cyclogenesis
• The dry spot is associated with descending motions at upper levels linked to a tropopause dynamic anomaly.
• During the development of cyclogenesis the dry spot extended in the WV imagery leading to a dry intrusion associated with further expanding of subsiding motion.
• A dry slot appears as a part of the descending air entering to the southwest of the surface low.
Conceptual model (Browning, 1997)
Dry intrusionDry intrusion:: Very dry air, which comes down to low levels near cyclones and forms a coherent region of dry air. Although re-ascending close to the cyclone centre, this dry air have normally had a long history of descent, the driest parts having been close to the tropopause upstream about two days earlier.
Conceptual model (Browning, 1997)
Dry intrusionDry intrusion:: Close to the cyclone center, horizontal transport plays a major role in producing variability of the upper troposphere flow. As a result, some of the dry air that has originally subsided also moves horizontally or even rises: This may produce potential instability and convection near the low center.
IDENTIFICATION OF IDENTIFICATION OF DRY INTRUSIONDRY INTRUSION FROM WV IMAGERYFROM WV IMAGERY
WV imagery is a tool for identifying dry intrusions
and it is useful for operational purposes:
• Monitoring dry intrusions may help the
forecaster to understand what is happening on
the mesoscale and to anticipate what may
happen over a period of a nowcast.
• This is especially valuable in situations of rapid
cyclogenesis, associated with convective activity,
when local warnings are needed.
Dry intrusion and kata- and Dry intrusion and kata- and ana-cold frontsana-cold fronts
• As regards to the WV imagery analysis of the dry intrusion, it is appropriate to be considered in relation to the conceptual models of kata- and ana-cold fronts.
• By means of a joint interpretation of WV imagery and model fields, we are able to note important characteristics of the frontal system.
kata- and ana-cold frontskata- and ana-cold fronts
Sections normal to the surface cold front (SCF) through idealised ana- and kata- cold fronts
purekata-front
pureana-front
Intermediate cold-front phase
Pure kata-cold frontPure kata-cold front
At the kata-cold front the dry-intrusion air overruns the surface cold front (SCF) for a distance of 10–200 kilometres. The dry-intrusion then terminates as an upper cold front (UCF) where the cloudiness deepens abruptly and often convectively.
At a kata-cold front: Low-level moist air is capped by dry air above.
DRY AIRDRY AIR
CLOUDSCLOUDS
UCF
MOIST AIRMOIST AIR
SCFSCF
DRY INTRUSIONDRY INTRUSION
Pure ana-cold frontPure ana-cold front
At the ana-front a subsiding circulation transverse to the front is generated. The leading edge of the dry intrusion then progresses with the surface cold front below the ascending warm moist air, which generates a wide cloud band behind the SCF
At the ana-cold front: Low-level dry air is capped by moist/cloudy air.
MOIST AIRMOIST AIRC L O U D B A N D
C L O U D B A N D
DRY INTRUSION
DRY INTRUSION
DRY AIRDRY AIR
SCFSCF
Kata-/ana-cold fronts in WV image Kata-/ana-cold fronts in WV image overlaied by overlaied by w w at 500 hPaat 500 hPa (blue) and (blue) and w w 925 hPa925 hPa (red) (red)
Ana cold front
Ana cold front
Kata cold front
Kata cold front
Upper cold front
Upper cold frontAt the ana front:At the ana front: The air is potentially dryer at 925 hPa (w < 8°C) than it is at
500 hPa (w > 8°C). Low-
level dry air is capped by moist air above.
At the kata front:At the kata front: The air is potentially dryer at 500 hPa (w < 8°C) than it is at
925 hPa (w > 8°C). Low-
level moist air is capped by dry air above.
Kata-cold frontKata-cold front
MOIST LAYER
LOW CLOUDS
HIGH CLOUDS
800 hPa
400 hPa
250 hPa
Surface CF
Upper CF
DRY INTRUSION
DRY INTRUSION
MOIST WARM FLOWMOIST WARM FLOW
WV channel WV channel responseresponseWV grey
shadeNEARLY BLACK
MEDIUM GREY
or
NEARLY WHITE
Ana-cold frontAna-cold front
LOW CLOUDS
HIGH CLOUDS
800 hPa
400 hPa
250 hPa
Surface CF
DRY INTRUSION
DRY INTRUSION
MOIST WARM FLOWMOIST WARM FLOW
WV channel WV channel responseresponseWV grey
shadeDARK GREY
NEARLY WHITE
MEDIUM GREY
CELLS
Dry intrusion and Dry intrusion and katakata-cold front-cold front
Kata cold front
Kata cold front
Upper cold front
Upper cold front
NEARLY BLACK
MEDIUM GREY
NEARLY WHITEWV channel responseWV channel response
Surface CF
HIGH CLOUDS
• Rearward the SCF• Between SCF and UCF
• Forward the UCF
LOW CLOUDS
Dry intrusion and Dry intrusion and anaana-cold front-cold front
Ana cold front
Ana cold front
WV channel responseWV channel responseDARK GREY
NEARLY WHITE
LIGHT GREY
Surface CF
HIGH CLOUDS
• Rearward the SCF
OPEN CELLS
• At the zone of SCF• Forward the SCF
CLOUDS
• Satellite WV imagery may serve as a significant data
source for inspection different moisture regimes in the
vicinity of synoptic scale weather systems.
• In addition to the pure imagery interpretation, WV
images superimposed with various NWP fields
provide a deep knowledge of the horizontal and
vertical flow patterns.
• Using this essential tool in forecasting environment
is a way to help assessing important ingredients of
the bad weather systems.
SummarySummary
ConclusionConclusion
• Just after receiving the first water vapor imagery from Meteosat-1 in 1977, it was recognized as a valuable tool for synoptic-scale analysis.
• Then, sequences of WV images superimposed with upper-level dynamical fields have been introduced in forecasting environment as a significant data source that enables:
• To provide knowledge of the motion field that may help in interpreting WV imagery focusing on the tropopause dynamic anomalies and cyclogenesis, and
• To highlight important elements of interaction between significant dynamical features that may be precursors for subsequent developments.
• Nowadays, the far more advanced system of MSG allows to use two WV channels, 6.2 and 7.3 m, with enhanced capabilities to follow the synoptic situation.
• When interpreting WV imagery for operational forecasting purposes, the following principles are important:
• To look at an animation of WV images in order to see changes in the dynamical gray-shade features;
• To superimpose various fields of the forecasting environment onto the WV image to gain insight into synoptic ingredients of the atmospheric situation ;
• By joint interpretation of WV imagery and dynamical fields, to identify the crucial elements responsible for strong development leading to severe weather.
• To keep a critical mind when considering the model fields: Priority must always be given to the observational data and satellite imagery.
ConclusionConclusion
ReferencesReferences
Browning, K. A. 1997. The dry intrusion perspective of extra-tropical cyclone development. Meteorol. Appl. 4, 317–324.
Hoskins, B., 1997. A potential vorticity view of synoptic development. Meteorol. Appl. 4, 325–334.
Santurette, P., Georgiev C. G., 2005. Weather Analysis and Forecasting: Applying Satellite Water Vapor Imagery and Potential Vorticity Analysis. ISBN: 0-12-619262-6. Academic Press, Burlington, MA, San Diego, London. Copyright ©, Elsevier Inc. 179 pp.
Weldon, R. B., Holmes, S. J., 1991. Water vapor imagery: interpretation and applications to weather analysis and forecasting, NOAA Technical. Report. NESDIS 57, NOAA, US Department of Commerce, Washington D.C., 213 pp.