Water Vapor Assimilation, Preliminary Results of

Correcting for Supersaturation

James Jung

Cooperative Institute for Meteorological Satellite Studies

University of Wisconsin - Madison

7 June 2013

Experiment Design

• Investigate removal of supersaturation in the analysis Clip supersaturation during each outer loop Incorporate penalty for supersaturation during

minimization

• Review model background error Look for potential to improve distribution

• Review quality control and assimilation weights of existing water vapor channels (MW and IR)

• Add IASI and CrIS water vapor channels

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Background

• Low resolution (T254) hybrid• Clip supersaturation at each outer loop

Most points come from model

• Penalize supersaturation during minimization changed to 50 vice .05

• No changes to observations or observation weights

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Time Series Analysis Differences

200 hPa Temperature Analysis Differences

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Sen T

Vir T

200 hPa Humidity Analysis Differences

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Sp Hu

Re Hu

Select levels 2012071100Zanalysis differences

48 hPa Specific Humidity

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Sp Hu

Re Hu

Experiment analysis Experiment - Control

107 hPa Humidity

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Sp Hu

Re Hu

Experiment analysis Experiment - Control

107 hPa Wind U and V component

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U com

V com

Experiment analysis Experiment - Control

498 hPa Humidity

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Sp Hu

Re Hu

Experiment analysis Experiment - Control

925 hPa Temperature

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Sen T

Vir T

Experiment analysis Experiment - Control

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Select levels 2012071100Z and 2012090100Z

analysis differences

48 hPa Specific Humidity

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yellow/red = increasedblue/purple = decreased

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107 hPa Specific Humidity

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yellow/red = increasedblue/purple = decreased

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196 hPa Specific Humidity

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yellow/red = increasedblue/purple = decreased

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Near Surface Temperature

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yellow/red = increasedblue/purple = decreased

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Temperature Time Series

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•Lighter colors (near zero) are better•At almost all levels, the experiment is better in the Northern and Southern Hemispheres.

control exp

control exp

Temperature Bias

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•Global average time series of temperature bias.•Temperature drifts colder that analysis at both (50 & 850 hPa) levels.•Water vapor adjustments reduce temperature drift

control exp

control exp

BetterWorse

BetterWorse

500 mb Anomaly Correlations

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•exp (red) has the supersaturation removed.•Just removing supersaturation has a positive impact on anomaly correlations

controlexp

controlexp

BetterWorse

BetterWorse

Concerns

• Poor vertical distribution of moisture increments.• Moisture changes are large above 200mb and almost

negligible at others (near surface).• Large near surface temperature changes over

Antarctica• Supersaturation does not seem to be just random

noise.

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Summary

• Removing supersaturation during the analysis changes the humidity field in the upper troposphere and stratosphere. generally dryer

• Forecast temperature drift with time is improved at most levels. Warm and cold biases are reduced

• Antarctica temperatures are colder in the analysis and forecasts.

• Anomaly correlations are showing a small improvements

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Questions

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