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 Carbon dioxide Water vapour 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) WeightFun.html 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 μm) –only during the day –snow/ice dark  Convective clouds with ice shield? (VIS/IR 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): , 14:25

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

IR: Meteosat: Ozone-channel (IR: μm)

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

Enhancement: Limited range of counts

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

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

Highly sophisticated MSG- interpretation

EUMETSAT: Meteosat 8 (6,2 – 10,8) μm  Overshootings? , 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 - WV7.3 G = Difference IR9.7 - IR10.8 B = Channel WV6.2 THE "AIRMASS" RGB (Jochen Kerkmann, EUMETSAT (MSG-interpretation guide)) Applications: Applications:Rapid Cyclogenesis, Jet Stream Analysis, PV Analysis Area: Area:Full MSG Viewing Area Time: Time:Day and Night

Airmass RGB Example (base: Jochen Kerkmann, EUMETSAT (MSG-interpretation guide)) In RGB ( / /6.2) images, dry descending stratospheric air related to high PVappears in reddish colours ! The values shown above (in the red box) correspond to the 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 - WV7.3overshooting tops G: VIS/IR3.9 - IR10.8optical thickness, phase, particle size, emissivity B: NIR1.6 - VIS0.6optical thickness, phase, particle size

RGB 05-06,04-09,03-01 Example: Severe Convection (J. Kerkmann, EUMETSAT) In RGB ( / / ) images, cold Cb tops with small ice particles appear in yellowish colours (Cbs with large ice particles appear in reddish colours) !

New Convective Development Top T. -65°C MSG-1, 5 June 2003, 11:15 UTC RGB "Severe convection" WV6.2 - WV7.3 / IR3.9 - IR10.8 / NIR1.6 - VIS0.8 (from Jochen Kerkmann, EUMETSAT)