slide 1 eumetsat fellow day, 9 march 2015 observation errors for amsu-a and a first look at the...

EUMETSAT Fellow Day, 9 March 2015

Observation Errors for AMSU-A and a first

look at the FY-3C MWHS-2 instrument

Heather Lawrence, second-year EUMETSAT fellow, ECMWF

Supervised by: Niels Bormann & Stephen English


AMSU-A Observation Errors


The AMSU-A Instrument

10 Temperature sounding

channels6 satellites: good global coverage

(RIP NOAA-16 June 2014)

Microwave Temperature Sounder


Chs 9 – 14: used globally after thinning and

VarQC

Chs 5 – 8: also screened for cloud, orography,

some sea-ice

6h metop-A, metop-B

orography

cloud

AMSU-A current data usage: clear-sky assimilation

Sea-ice, orography


New Observation Errors and screening part 1: channels 5 - 8

OLD METHOD

orography

cloud

cloud

orography

NEW METHOD

• Clear-sky forward model RTTOV

• Filter cloud and orography

• Constant observation errors

• Clear-sky forward model RTTOV

• Keep some cloud and orography

• Use more physical observation errors


Different satellite instruments have

different noise terms:

Instrument NedT

Cha

nnel

Num

ber

NedT values from Nigel Atkinson, UKMO

NOAA-18

Aqua

Cha

nnel

Num

ber

Observation Error

Aqua

NOAA-18

Use different observation errors for

different satellite AMSU-As:

New Observation Errors and screening part 2: Satellite-dependent Observation Errors


New Observation Errors and Screening

1. Situation-dependent observation error model for channels 5 – 7

2. Remove first guess check for channels 6 – 8 in cloudy regions (use lwp and scatter index check)

3. Replace orography screen with observation error screen over land

4. Satellite-dependent observation errors

Increased number of used data:

Ch 5 - 6: orography Ch 6 – 8: over ocean

ch 5: 6%

ch 6: 11%

ch 7: 8%

ch 8: 3%


SUMMER: Improved fit of 12-hour forecast

to ATMS

improvement

SUMMER: improved forecast scores

Contribution to CY41R2

Impact on forecast accuracy

WINTER: neutral forecast scores

No

rma

lise

d d

iffe

ren

ce

Forecast day

No

rma

lise

d d

iffe

ren

ce

Forecast day

WINTER: Improved fit of 12-hour forecast

to ATMS

improvement

improvement

6 months of Assimilation Trials with:


FY-3C MWHS-2

MWTS

MWHS

MWRI

IRAS

MWTS-2

MWHS-2

IRAS

MWRI

GNOS

See Lu et al (2011a & b), Chen et al (2014).

FY-3B MWHS assimilated operationally since September 2014.


China’s FY-3 polar orbiting satellite series

FY-3A/B: launched 2008, 2012

FY-3C: launched Sep 2013


CMA

ECMWF UKMO

FY-3C collaboration

Qifeng Lu, et al

Bill Bell, Katie Lean, Nigel

Atkinson…

• Regular teleconferences, feeding back findings to CMA

• My focus: MWHS-2


FY-3C MWHS-2 study

Use a 6 month sample dataset to:

1. Assess data quality

2. Prepare for All-sky assimilation


• Keep all cloud-affected data

• Apply higher observation errors in cloudy regions

• Use an all-sky forward model RTTOV-SCATT

e.g. MHS channel 4 observations MHS channel 4 observation errors

All-sky Assimilation

All-sky Assimilation reference: Alan Geer et al (2014), ECMWF Tech. Memo 741:

http://old.ecmwf.int/publications/library/do/references/show?id=91235

AIM: Assimilate in all-sky conditions


MWHS-2 Instrument

5 183 GHz channels like ATMS (similar to MHS)

8 new 118 GHz channels


• 10:30 descending orbit

• 90 FOV (scan angles)

• Swath of 2700km

• Horizontal resolution 16 km (183 GHz) 32 km (118 GHz)

MetOp-B MHS

Suomi-NPP ATMS

FY-3C MWHS-2

MWHS-2 Instrument


MWHS-2 183 GHz channels

5 183 GHz channels


1. Compare Observations to ECMWF background

MWHS-2 Channel 13 Observation - Background

The main differences are cloud features


2. Compare to Other Instruments

MWHS-2 channel 13 ATMS channel 20

Maps of observation minus background look very similar…


mean(o-b) mean(o-b) stdev(o-b)

MW

HS

-2 c

ha

nn

el n

um

be

rMonthly mean and standard deviation of o-b

• Higher biases than ATMS and MHS

• Similar standard deviation

MWHS-2

ATMS all-sky

MHS all-sky

1 month, cloud-filtered

Mean before bias correction Mean after bias correction Standard deviation

window

channels

High

peaking

Low peaking


183 GHz Data Quality: Summary

• Higher global biases for some channels (14 and 15)

• Most bias removed by the ECMWF Variational Bias Correction Scheme

• Standard deviation of background departures similar to ATMS/MHS


Assimilation Trials for 183 GHz channels

Objective:

• Test the quality of the data in the full observing ECMWF

system

• Prepare for operational assimilation

Assimilation Trials:

1. Control: Full observing system T511 horizontal resolution

2. Full assimilation: Assimilate all 5 channels globally


Temperature: 1 – 2% change Vector Wind: 1 – 2 % change

Humidity: 1 – 5 % change

Assimilation Trial Results: Change in Analysis Increments

6 months data

Change in root mean square (12h forecast – analysis):

0.04

0.02

-0.02

-0.04

0.00


Change in short-range forecasts (12-hour)Improved fits to humidity observations:

AIRSIASI

ATMSMHS

improvementimprovement

improvementimprovement


Change in 1 – 10 day forecasts

No significant change to forecast scores:

improvement

degradation

e.g. geopotential and vector wind at 500hPa over Southern Hemisphere

Forecast Day Forecast Day

Nor

mal

ised

Diff

eren

ce

stde

v(fc

– a

n)

6 months data


Summary

Assimilating 183 GHz MWHS-2 channels over 6 months leads to:

• Increased increments of humidity, vector wind, temperature

• Improved fits of other observations to 12-hour forecasts (ATMS, IASI, AIRS)

• Neutral impact on forecast scores (days 1 – 10 forecasts)


FY-3C MWHS-2: 118 GHz channels


118 GHz:

• Oxygen band – Temperature sensitivity

• Water vapour continuum – Humidity sensitivity

• Cloud effects: absorption, emission, strong

scattering

MWHS-2 118 GHz channels

8 new 118 GHz channels


MWHS-2 118 GHz channel clear-sky Jacobians

• Channels 2 – 4: Temperature

• Channels 4 – 6: Temperature + cloud

• Channel 7: Temperature + cloud + humidity


Observation minus model background: Striping

STRIPING observed

MWHS-2 ch 3:

MetOp-B AMSU-A ch 9:ATMS ch 10 (unaveraged):1.4 K scale

5 K scale

2 K scale


Observation minus model background: cloud information6 K scale

16 K scale

channel 6

channel 7


Monthly mean observation minus background

Before bias correction After bias correction

MWHS-2

ATMS clear-sky

MetOp-B AMSU-A all-sky

All AMSU-A’s all-sky

1 month, filtered for cloud:


• Cloud-free Temperature information noisier than AMSU-A/ATMS

Monthly standard deviation of observation minus background

1 month, filtered for cloud:


3 month All-sky Assimilation Trials:

• Control

• Assimilate channels 2 – 7 over ocean

118 GHz First Assimilation Trials

Apply higher observation errors to cloud-affected data for channels 5 - 7:

Channel 7 observation error


Mostly neutral:

Small degradation of 1000hPa temperature:

Results: Impact on Forecast Accuracy

Work is still ongoing

Forecast day


MWHS-2 118 GHz channels: Summary

• New channels with temperature, humidity, cloud sensitivity

• Potential for additional cloud information

• Temperature information more noisy than AMSU-A, striping observed

• On-going experimentation with 118 GHz channels – attempting to use them

in all-sky (Will 4DVar be able to correctly adjust temperature, humidity

increments?)


Summary


AMSU-A:

• New Situation-dependent observation errors: AMSU-A channels 5 - 7

• Satellite-dependent observation errors: AMSU-A channels 5 – 13

• Introduced more data over orography and ocean for channels 5 - 8

• New observation errors and screening changes are implemented in CY41R2 with a

small positive impact on short-range forecasts

FY-3C MWHS-2:

• FY-3C MWHS-2 183 GHz data quality looks comparable to ATMS

• FY-3C MWHS-2 118 GHz channels have higher noise than AMSU-A but more cloud

information

Summary


Ongoing and Future work

• Monitor FY-3C MWHS-2 183 GHz channels and make operational (winter

2015?)

• Investigate further the usage of the new 118 GHz channels


Thank you for listening!

Any questions?

slide 1 eumetsat fellow day, 9 march 2015 observation errors for amsu-a and a first look at the...

Documents

ecmwf eumetsat fellow

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new observation errors

observation error screen

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allsky assimilation

b mwhs

different satellite