Water-Vapor Analysis Uncertainty
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Water-Vapor Analysis Uncertainty and Implications for Storm-Scale Radar-Data Assimilation David Dowell and Curtis Alexander NOAA ESRL GSD AMB, Boulder, CO Acknowledgments: Ming Hu, Steve Weygandt, Tanya Smirnova, Stan Benjamin, John Brown, Eric James, Patrick Hofmann, Jian Zhang.

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Hourly Updated NOAA NWP Models

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Hourly updated noaa nwp models

Water-Vapor Analysis Uncertaintyand Implications for Storm-ScaleRadar-Data AssimilationDavid Dowell and Curtis AlexanderNOAA ESRL GSD AMB, Boulder, COAcknowledgments:Ming Hu, Steve Weygandt, Tanya Smirnova, Stan Benjamin, John Brown, Eric James, Patrick Hofmann,Jian Zhang


Hourly updated noaa nwp models

Hourly Updated NOAA NWP Models

Rapid Refresh (RR)

replaces RUC at NCEP in 2011

WRF, GSI with RUC features

13km Rapid Refresh (mesoscale)

13km RUC (mesoscale)

3km HRRR (storm-scale)

RUC – current oper

Model, new 18h fcst

every hour

High-Resolution

Rapid Refresh

Experimental 3km nest inside RR, new 15-h fcst every hour


Noaa esrl gsd amb models

NOAA/ESRL/GSD/AMB Models


Hrrr reflectivity verification

HRRR Reflectivity Verification

Eastern US, Reflectivity > 25 dBZ

11-20 August 2011

BIAS 03 km

CSI 40 km

RUC->HRRR Radar

RR->HRRR Radar

RR->HRRR No Radar

RUC->HRRR No Radar

Optimal

RR->HRRR Radar

RR->HRRR No Radar

RUC->HRRR Radar

RUC->HRRR No Radar

Reflectivity DA in RR/RUC increases HRRR forecast skill

HRRR bias depends strongly on parent model


Noaa esrl gsd amb models1

NOAA/ESRL/GSD/AMB Models


Hourly updated noaa nwp models

more accuraterepresentation ofsystem maturity

convection develops quickly (RR cycling, DDFI)

obs

1-h fcstwithout 3-kmradar DA

1-h fcstwith 3-kmradar cycling

1-h fcstwith 3-kmradar DA

CompositeReflectivity2100 UTC11 May 2011


Hourly updated noaa nwp models

more accurateforecast ofconvective system propagation

obs

6-h fcstwithout 3-kmradar DA

6-h fcstwith 3-kmradar DA

CompositeReflectivity0200 UTC11 May 2011


Hourly updated noaa nwp models

spurious

convection

spurious

convection

obs

6-h fcstwithout 3-kmradar DA

6-h fcstwith 3-kmradar DA

CompositeReflectivity0200 UTC11 May 2011


Impressions from reflectivity data assimilation on hrrr x 3 km grid

Impressions from Reflectivity DataAssimilation on HRRR (x=3 km) Grid

  • Forecast skill from radar DA

    • Improvement in 00-03 hr forecasts

    • Little change in 06-12 hr forecasts

    •  meso-/synoptic-scale forcing quickly dominates forecast?

    • Model inability to sustain some observed storms

    • Convective-scale model error

    • and/or storm-environment analysis error?

    • Spurious convective storms

    • Pervasive problem

    • Unclear solution on convective scale


Back to the mesoscale

Back to the Mesoscale

  • Rapid Refresh (RR) and Rapid Update Cycle (RUC)

    • Similarities: resolution (Dx=13 km), 3DVar DA, hourly cycling

    • Differences: resulting HRRR forecasts

    • How different are the RR and RUC mesoscale analyses?

    • Two realizations of a mesoscale analysis

    • Differences representative of analysis uncertainty?

RR->HRRR No Radar

RUC->HRRR No Radar

Optimal

BIAS 03 km


Rr and ruc temperature bias

RR and RUC Temperature Bias

CONUS

All 00/12 UTC Raobs

08 July – 08 Sept 2011

00 hr (analysis)

12 hr fcsts

RR

RUC

RR - RUC

RR

RUC

RR - RUC

Very small temperature bias in both RR and RUC


Rr and ruc humidity bias

RR and RUC Humidity Bias

CONUS

All 00/12 UTC Raobs

08 July – 08 Sept 2011

00 hr (analysis)

06 hr fcsts

RR

RUC

RR - RUC

RR

RUC

RR - RUC

RUC/RR drier/moister below 650 mb, opposite above

RR a closer fit to the observations by 6 hrs in lower trop

Water vapor is the dominant source of the RH bias


Rr and ruc humidity bias1

RR and RUC Humidity Bias

CONUS

All 00/12 UTC Raobs

11-22 August 2011

NO RADAR DA

00 hr (analysis)

06 hr fcsts

RR

RUC

RR - RUC

RR

RUC

RR - RUC

Without radar DA, model bias even more pronounced


Hrrr water vapor histograms

HRRR Water Vapor Histograms

CONUS

11-22 August 2011

NO RADAR DA

0 hr forecasts

Surface

~800 mb

RUC->

HRRR

higher

RR->

HRRR

higher

RUC->

HRRR

higher

RR->

HRRR

higher

Differences large enough to affect convective forecasts


Hrrr reflectivity verification1

HRRR Reflectivity Verification

Eastern US, Reflectivity > 25 dBZ

11-20 August 2011

NO RADAR DA

04 hr fcsts

BIAS 03 km

CSI 40 km

Optimal

Same Skill

No difference

RR->HRRR

RUC->HRRR

RR->HRRR – RUC->HRRR

RR->HRRR

RUC->HRRR

RR->HRRR – RUC->HRRR


Hrrr reflectivity verification2

HRRR Reflectivity Verification

Eastern US, Reflectivity > 25 dBZ

11-20 August 2011

NO RADAR DA

04 hr fcsts

BIAS 03 km

CSI 40 km

Optimal

Same Skill

No difference

RR->HRRR

RUC->HRRR

RR->HRRR – RUC->HRRR

RR->HRRR

RUC->HRRR

RR->HRRR – RUC->HRRR


Hourly updated noaa nwp models

CompositeReflectivity0800 UTC13 Aug 2011

obs

storm coverage somewhat underforecast (overforecast) in

RUC->HRRR

(RR->HRRR)

2-h fcstRUC->HRRR

2-h fcstRR->HRRR


Hourly updated noaa nwp models

Water Vapor

Analyses

8 m AGL0600 UTC13 Aug 2011

RR – RUC

difference

storm coverage somewhat underforecast (overforecast) in

RUC->HRRR

(RR->HRRR)

RUC->HRRR

RR->HRRR


Hourly updated noaa nwp models

Water Vapor

Analyses

2600 m AGL0600 UTC13 Aug 2011

RR – RUC

difference

storm coverage somewhat underforecast (overforecast) in

RUC->HRRR

(RR->HRRR)

RUC->HRRR

RR->HRRR


Hourly updated noaa nwp models

Analysis

Vertical

Profiles0600 UTC13 Aug 2011

RR->HRRR

RUC->HRRR

RR->HRRR


Hourly updated noaa nwp models

CompositeReflectivity1500 UTC14 Aug 2011

obs

spurious convection

in RR->HRRR

3-h fcstRUC->HRRR

3-h fcstRR->HRRR


Hourly updated noaa nwp models

Water Vapor

Analyses

8 m AGL1200 UTC14 Aug 2011

RR – RUC

difference

location of

spurious convection

in RR->HRRR

RUC->HRRR

RR->HRRR


Hourly updated noaa nwp models

Water Vapor

Analyses

600 m AGL1200 UTC14 Aug 2011

RR – RUC

difference

differences

as much as

10 g/kg !

RUC->HRRR

RR->HRRR


Hourly updated noaa nwp models

Analysis

Vertical

Profiles1200 UTC14 Aug 2011

RR->HRRR

Observed

Profile

RUC->HRRR

RR->HRRR


Water vapor analysis

Water-Vapor Analysis

  • Small analysis differences near surface

    • Abundance of surface observations

  • Large analysis differences (several g/kg) at low levels above surface

  • Much larger than what is considered important for

    • convective-storm formation and evolution

    • Limited potential of storm-scale radar DA in the presence of large water-vapor analysis and forecast errors

    • Spurious convective storms

    • Model inability to sustain some observed storms

    • Reducing analysis uncertainty and bias

    • Radar and/or satellite data?

    • DA methods? => 3DVar cloud analysis; flow-dependent b. e. c.

    • Model improvements? => PBL scheme


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