ECMWF analysis of the AIRS focus-day 20 July 2002 Tony McNally / - - PowerPoint PPT Presentation

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ecmwf analysis of the airs focus day 20 july 2002
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ECMWF analysis of the AIRS focus-day 20 July 2002 Tony McNally / - - PowerPoint PPT Presentation

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ECMWF analysis of the AIRS focus-day 20 July 2002 Tony McNally / Phil Watts / Marco Matricardi Introduction Detection of clear channels Clear-sky departure statistics preliminary 3DVAR assimilation results status and plans

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ECMWF analysis of the AIRS focus-day 20 July 2002

  • Introduction
  • Detection of clear channels
  • Clear-sky departure statistics
  • preliminary 3DVAR assimilation results
  • status and plans

Tony McNally / Phil Watts / Marco Matricardi

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ECMWF cloud detection algorithm for AIRS

  • Exploits NWP model accuracy

(particularly in mid-upper trop constrained by AMSUA)

  • Aims at dynamically finding

clear channels rather than completely clear locations

  • So far validated with simulated

cloudy AIRS radiances

  • Extendable to CrIS / IASI

Observed cloudy spectra and simulated clear-sky (NWP) spectra Non-linear transformation to cloud-ranked channel space Pattern recognition algorithm (currently digital filter used) Channels split into bands (LW/SW/6m/O3) by cloud effect

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SLIDE 3

ECMWF cloud detection scheme

Cloudy channels Clear channels

Observed - computed radiance departures

(example for LW band from AIRS focus day)

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Distribution of data flagged clear

AIRS channel 145 (14.5micron similar to HIRS channel 3 100hPa) AIRS channel 1694 (6.7micron similar to HIRS channel 12 400hPa) AIRS channel 226 (13.5micron similar to HIRS channel 5 600hPa) AIRS channel 787 (11 micron similar to HIRS channel 8 window)

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SLIDE 5

ECMWF detection of clear channels

AIRS channel 145 (14.5micron similar to HIRS channel 3 100hPa) clear cloudy

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ECMWF detection of clear channels

AIRS channel 1694 (6.7micron similar to HIRS channel 12 UTH) clear cloudy

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SLIDE 7

ECMWF detection of clear channels

AIRS channel 226 (14.0micron similar to HIRS channel 5 600hPa) clear cloudy

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SLIDE 8

ECMWF detection of clear channels

AIRS channel 787 (11micron similar to HIRS channel 8 window) clear cloudy

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SLIDE 9

Frequency of AIRS channels flagged CLEAR

(Longwave Band only)

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SLIDE 10

Frequency of AIRS channels flagged CLEAR

(Whole AIRS spectrum)

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SLIDE 11

AIRS clear-sky radiance departures from the ECMWF model

The ECMWF model fields (T/Q/O3) are interpolated to the AIRS locations and are valid to within 1hour of the

  • bservation time.

Clear-sky radiances for each AIRS channel are then computed using the RTTOV radiative transfer model using SRFs supplied by L.Strow. The statistics are: (Observed AIRS radiance) minus (ECMWF-RT)

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SLIDE 12

AIRS radiance departures from ECMWF model

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SLIDE 13

AIRS radiance departures from ECMWF model

Stratospheric +ve ECMWF model bias suggested by

  • ther instruments
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SLIDE 14

AIRS radiance departures from ECMWF model

Negative (moist) bias suggested by

  • ther instruments
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SLIDE 15

AIRS radiance departures from ECMWF model

No solar radiation currently modeled

RTTOV on 43 levels

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Preliminary assimilation of real AIRS radiances

  • Assimilation scheme : 3DVAR
  • Assimilation window : 6hrs
  • Model resolution : TL159 (60 levels)
  • Data used : All conventional + AIRS radiances
  • AIRS channel selection : clear only from 281 NRT
  • Observation errors : 1.0K in each channel

Experimental details:

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SLIDE 17

Channel use in 3DVAR assimilation based

  • n clear flags

Tail pressure of lowest AIRS long-wave channel determined cloud-free (2002-07-20 real AIRS radiances)

Low cloud

  • r clear

Mid-level cloud cover High level cloud cover

Temperature weighting functions

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SLIDE 18

Temperature increments in ECMWF 3DVAR due to AIRS clear channel radiance assimilation

Temperature increments in (K) at 200hPa for 2002-07-20 for 06z (red

  • range positive / green-blue negative)

The plots shows the active use of channels above low cloud causing temperature adjustments to the analysis in the mid-upper troposphere

AIRS-787 window channel (obs-fg)

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SLIDE 19

Summary of results for AIRS focus-day

  • Cloud detection of clear AIRS channels working

well but requires detailed validation with MODIS imagery

  • Instrument radiance data generally simulated very

well from NWP model using RTTOV radiative transfer (soon to be upgraded to 90 levels + new spectroscopy)

  • Preliminary assimilation looks very encouraging, but

sensible NWP impact trials pending NRT data flow and final SRFs.

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Current schedule for AIRS assimilation at ECMWF

  • Focus day (2002-07-20) data released by NASA in late August
  • Analysis of focus day data (in progress)
  • Initial re-tune of RT model (complete)
  • NRT data activated by NESDIS ORA (October 2002)
  • Activation of real-time monitoring results on ECMWF WWW
  • Second (final ?) retune of RT model from NASA (end of 2002)
  • Residual bias evaluation / correction
  • NRT assimilation to evaluate NWP performance (spring 2003)
  • Day-1 (conservative) Operational assimilation (late spring 2003)
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SLIDE 21

Low pass filter : di

Grad (i) < m and d(i) < t

Initialize i = i low increment i = i + 1

flag > I clear flag < I cloudy

yes no

Notes:

ilow is the channel ranked most sensitive to cloud

  • the gradient is evaluated over

(+1) and (+5) steps to avoid stopping as local max/min. The threshold is 0.001 ? The gradient is checked negative

  • ver cold surface and positive
  • ver warm surfaces.
  • window channels are

excluded that show surface (e.g. emissivity) features more than a monotonic cloud signal and cause dangerous termination when the clear-sky emission is poorly computed.

  • the departure threshold is + / -

0.5K depending on surface type