characteri s ing the fy-3a microwave temperature sounder using the ecmwf model

VAISALA Award Lecture

Characterising the FY-3A Microwave Temperature Sounder Using the ECMWF Model

Qifeng Lu, William Bell, Peter Bauer, Niels Bormann and Carole Peubey

National Satellite Meteorological Center, CMA, BeijingEmail: [email protected]

ECMWF

Thanks to all who contributed to this work


Outline

Microwave sounding data in NWP and climate research: operational satellites from the US, Europe & China : 1978-2020

China’s FY-3A satellite: The Microwave Temperature Sounder (MWTS)

Identifying and characterising MWTS biases using NWP fields:

Passband shifts

Radiometer non-linearities

Improved Assimilation of MWTS

Summary and conclusion

Next Steps: Early results from the evaluation of MSU and AMSUA from 1978-2011


US

Europe

China

• Microwave sounding data provides information on temperature and humiditywhich has been widely used in :

• Operational NWP data assimilation systems and;• Climate research – to determine long term trends in atmospheric state

• The US has launched a series of polar satellites, dating back to 1978;• Europe began to contribute in 2006 (MetOp-A)• China began to contribute in 2008 (FY-3A)

Operational Sounding Satellites


The importance of MW sounding data in NWP

Largest positive impact (per system)is obtained from microwavetemperature sounding data

Forecast sensitivity toobservations (FSO)Is an adjoint based technique for assessing the influence of observing systems on forecast accuracy

(from C. Cardinali, ECMWF)

VAISALA Award Lecture 5

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Microwave TemperatureSounder (MWTS)4 channel (~MSU)

Microwave HumiditySounder (MWHS)5 channel (~MHS)

InfraredAtmospheric Sounder(IRAS) 20 channels (~HIRS/3)

Microwave Radiation Imager10 channels (~AMSR-E)

The FY-3A/B Instrument Suite


Comparison of MWTS and AMSU-A Brightness Temperatures

State dependent inter-satellite (MWTS vs AMSU-A) biases:

Region 1 (tropics): MWTS TBs warm relative to AMSU-ARegion 2 (high northern latitudes) : No significant bias

Brightness temperature map from cycle 2008091700

Characterize the MWTS

1

2


MWTS & AMSU-A Channel Specifications

• Microwave temperature sounders operate at 50-60 GHz in the O2 absorption band• The frequency of the channel pass band centre determines the layer sounded• MWTS is a 4 channel instrument, similar to earlier US MSU instruments• AMSU-A is a 14 channel radiometer.


4

3

2

State dependence of frequency drifterrors : lapse rate dependence

• Passband shifts raise / lower the weighting function peak• The resulting TB bias depends on the local temperature lapse rate


Schematic of error terms


Optimisation of pass band centre frequency estimates

Pass band centres:

design spec.measuredoptimised

• Shifts exist relative topre-launch measurements


MWTS Radiometer Non-linearity

ΔTMAX

FIRST GUESS DEPARTURES • design specified pass band• pre-launch measured• optimised• non-linearity corrected


MWTS-2 MWTS-3 MWTS-4

First Guess Departures (K) ,i.e.,Observation minus Simulation

Pre-launch measured passband

Optimised passband

• from line-by-line modelling• uncertainties of ~32-55 MHz detected and corrected

Non-linearity corrected

AMSU-A equivalent

Characterising the FY-3A MWTS:Detecting and Correcting passband errors and Non-linearities


MWTS OSEs Forecast Verification: Z at 200, 500 and 700 hPa

Improvementdue to MWTS data

Normalised differences in RMSErrors in Z, verified against own analysis90% confidence intervals shown

Small improvementsin SH in going from:

original data

→ recalibrated (low weight)

→ recalibrated (high weight)

NH close to neutralwith some benefit in recalibrated data

PRELAUNCH_MWTS(full system + original MWTS data)

HIOBSERR_MWTS(Full system + optimised MWTSwith low weight)

LOWOBSERR_MWTS(Full system + optimised MWTSwith high weight)


Summary FY-3A data has been evaluated at ECMWF through a comparison with simulated

radiances & full assimilation experiments in which FY-3A data is introduced in the

ECMWF system.

The study revealed, and corrected, biases in FY-3A MWTS related to :

Uncertainties in the passband centre frequencies

Radiometer non-linearities

These corrections bring the MWTS data close to the quality of equivalent AMSU-A

data & in assimilation experiments this MWTS data delivers improvements in forecast

accuracy.

The high value of NWP in Cal/Val of new satellite sensors has been clearly

demonstrated – further improvements in FY-3A and FY-3B data are expected, and it is

hoped NWP will again play a crucial role for FY-3C, …. FY-3G !

A powerful new general approach to diagnosing an important group of biases

affecting microwave sounders has been developed.

This work demonstrates the significant benefits of close collaboration between

satellite agencies and NWP centres.


Next Steps: Initial results from an evaluation of MSU and AMSUA from

1978


MSU CH3 (54.96 GHz): NOAA-6 to NOAA-14Fr

eque

ncy

Shift

/ M

Hz

STD

(FG

_DEP

)Im

prov

emen

t in

STD

(FG

_DEP

)

• LbL modelling based on ERA-Interim fields• 1 cycle per month: 1979 -2011

•Blue dots represent FG_DEP after shift correction•Colour dots before


Finally … Thanks !

The authors are honored to receive the Second Vaisala Award for 2012 and are very grateful to the Award Committee for recognising our work.

We would also like to acknowledge the contribution of colleagues from across the world (from CMA, ECMWF, UK Met Office and others besides) who made this work possible

And finally - thanks to the local CIMO-TECO-METREOREX organising committee for their hospitality here in the wonderful city of Brussels !

characteri s ing the fy-3a microwave temperature sounder using the ecmwf model

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