Purpose

• To deepen your knowledge of satellite images' interpretation Preparation for the succeeding part about summer convection

Pre-requesites

• Learning modules from EUMETSAT

• Online-presentation "Convection"

Content

1. Physical background

2. Limitations

3. Monochromatic images- Colour tables

4. Highly sophisticated RGBs

5. Examples

Physical background – brief repitition

Solar and thermal radiation in relation to Meteosat channels and to absorption bands (talk by Marianne Koenig)

Wavelength (μm)

Thermal radiationsolar radiation

Absorption-bands

Ozone

Carbondioxide

Watervapour

W/m²/λ

Meteosat-channels (without HRV)

Contribution Functions

Influences to weighting functions

Klick upon the link below and try different combinations of– gas mixing ratio– line halfwidth– line strength– distance from the centre of the absorption band– scale height

(Tom Whittaker and Steve Ackermann)

http://cimss.ssec.wisc.edu/wxwise/class/aos340/spr00/WeightFun.html

Technical background(channels)

Meteosat -channels

• 12 channels (μm)– VIS/NIR: 0.6 / 0.8 /1.6– HRV: 0.5 – 1.1– WV: 6.2 / 7.3– IR: 3.8 / 8.7 / 10.8 / 12– Pseudo-Soundings: 9.7 / 13.4

• Horizontal resolution (Middle Europe)– HRV : 2 km– "others": 5 km

Cloud amount (problems)

• Horizontal resolution: scattered Cu, Sc– HRV (first identification of convection's onset)– NOAA most suitable in Central Europe (however poor

temporal resolution problems for nowcasting)

• Contrast– VIS higher than IR

• Transparency (Ci, edges of Cb)– VIS underestimation of cloud amount

• Low clouds– IR (temperatures of cloud tops and the earth surface

similar) difficult to identify clouds (e.g., fog)

Cloud top height

• most suitable: radiosoundings in a relevant area

• more reliable results– sharp and smooth cloud tops (e.g., St, Cb-anvil)

• less reliable results (yielding too low tops)– scattered cloudiness– thin Ci

Meteosat-Product: Cloud top height

Channels 1.6 and 3.9 μm

• (NIR 1.58 - 1.64 μm)– only during the day– snow/ice dark

Convective clouds with ice shield?

• (VIS/IR 3.55 - 3.93 μm)– day and night– during the night and in the case of small droplets „colder“– during the day CBs with small ice particles „warmer“

(IR+VIS defined according to IR-temperature) intense convection / updraft

Meteosat: NIR 1.6 μm

Ice clouds - cirrus

Meteosat: VIS/IR 3.9 μm (equalizing)

low clouds

Meteosat: IR 10.8 μm (for comparison)

NOAA (RGB+Kanal 3B): 30.05.97, 14:25

Characterisation of cloud top structures (overshooting tops, plumes) ofstorms over Spain and Portugal using the 3.9 mm channel on NOAA

AVHRR (M. Setvak, Czech NMS)

30 May 1997, 14.25 UTC, RGB image (ch. 1, 2, 4) 30 May 1997, 14.25 UTC, enhanced ch. 3 (3.9 mm)

Analysis and diagnosis with coloured images

• purposes– better and simplified identification of relevant cloud

areas– specific analysis of critical thresholds

• two alternatives– colouring of monospectral images– composites (multi-spectral)

Monospectral diagnosis (critical thresholds)

• definition of relevant thresholds icing (< 10°C) (depending among other in aircraft) probability of precipitation (< -10°C, in "warmer

regions") thunderstorms (<-25°C (summer, middle latitudes)) hail (<-55 to -60°C (summer, middle latitudes))

Meteosat: IR 10.8 μm (enhanced)

Channels within absorption bands

Meteosat: Ozone-channel (IR: 9.38-9.94 IR: 9.38-9.94 μm)

Meteosat: water vapour-channel (WV: 5.35-7.15 WV: 5.35-7.15 μm)("original")

Enhancement: Limited range of counts

Meteosat: water vapour-channel (WV: 5.35-7.15 WV: 5.35-7.15 μm)(equalizing)

Meteosat: water vapour-channel (WV: 6.85-7.85 WV: 6.85-7.85 μm)(equalizing)

Highly sophisticated MSG-interpretation

EUMETSAT: Meteosat 8 (6,2 – 10,8) μm Overshootings?

09.06.2004, 07 UTC. (WV 6.2 μm minus IR 10.8 μm)V-structure (not quite clear) and WV 11.4 K warmer than IR (tip with the strongest updraft,round-shaped structures!)

R = Difference WV6.2 - WV7.3G = Difference IR9.7 - IR10.8B = Channel WV6.2

THE "AIRMASS" RGB(Jochen Kerkmann, EUMETSAT (MSG-interpretation guide))

Applications:Applications: Rapid Cyclogenesis, Jet Stream Analysis, PV AnalysisArea:Area: Full MSG Viewing AreaTime:Time: Day and Night

Airmass RGB Example(base: Jochen Kerkmann, EUMETSAT (MSG-interpretation guide))

6.2-7.3

9.7-10.8

6.2

In RGB (6.2-7.3/9.7-10.8/6.2) images, dry descending stratospheric air related to high PVappears in reddish colours !

The values shown above (in the red box) correspond tothe location (shown by an arrow) on the next slide !

MSG-1, 7 January 2005, 22:00 UTC

Airmass RGB Example: high PV(base: Jochen Kerkmann, EUMETSAT (MSG-Interpretation guide))

Differences and applications RGB "Severe convection" – only during day

(base: Jochen Kerkmann, EUMETSAT)

R: WV6.2 - WV7.3 overshooting tops

G: VIS/IR3.9 - IR10.8 optical thickness, phase,particle size, emissivity

B: NIR1.6 - VIS0.6 optical thickness, phase,particle size

RGB 05-06,04-09,03-01 Example:Severe Convection (J. Kerkmann, EUMETSAT)

6.2 - 7.3

3.9 - 10.8

1.6 - 0.6

In RGB (6.2-7.3/ 3.9-10.8/1.6-0.6) images, cold Cb tops with small ice particlesappear in yellowish colours (Cbs with large ice particles appear in reddish colours) !

New Convective

DevelopmentTop T. -65°C

MSG-1, 5 June 2003, 11:15 UTCRGB "Severe convection" WV6.2 - WV7.3 / IR3.9 - IR10.8 / NIR1.6 -

VIS0.8(from Jochen Kerkmann, EUMETSAT)