# Presentation: 696607

## Comparison of  Some GDAS BiasesOperations versus ParallelDr. Bradley Ballish NCEP/NCO/PMB29 March 2007 

*“**Where America’s Climate and Weather Services Begin”*
* *

## Overview

**Operational temperature changes at 250 hPa**
**Operational radiosonde temperature biases at 250 hPa**
**Operational AMDAR temperature biases at 250 hPa**
**Parallel radiosonde temperature biases at 250 hPa**
**Monthly averaged operational height changes (analysis minus guess) at 700 hPa **
**Monthly averaged observed surface pressure biases**
**Conclusions**

## Operational Temperature Changes at 250 hPa

**Next 2 slides show monthly average temperature changes – analysis minus guess for January 2007 at 250 hPa**
**Some moderate changes can be explained by warm aircraft biases as found in the aircraft bias correction work with Krishna Kumar**
**The cold changes over the area north of the Himalayas appear to be a significant problem unrelated to aircraft data**

## Slide 4

## Slide 5

## Operational Radiosonde Temperature Biases at 250 hPa

**The next two slides show monthly averaged radiosonde temperature biases in tenths of degrees in  ****blue**** and analysis minus guess in ****red**** for 2-24 to 3-26 2007 for 250 hPa +/- 25 hPa non gross data**
**Radiosonde WMO Types are in ****green**
**Need at least 14 observations to plot**
**Different radiosonde types are showing large cold biases**

## Slide 7

## Slide 8

## Operational AMDAR Temperature Biases at 250 hPa

**The next slide shows monthly average temperature biases in tenths of degrees for AMDAR data on 10x10 degree grid in  ****blue**** and analysis minus guess in ****red**** for 12Z January 2007 for 250 hPa +/- 25 hPa non gross data**
**Need minimum count of at least 20 to plot**
**The AMDAR biases are warm in most areas except north of the Himalayas**
**This suggests the operational guess is too warm north of the Himalayas**

## Slide 10

## Parallel Radiosonde Temperature Biases at 250 hPa

**The next two slides show monthly averaged radiosonde temperature biases in tenths of degrees in  ****blue**** and analysis minus guess in ****red**** for 2-24 to 3-26 2007 for 250 hPa +/- 25 hPa non gross data**
**Radiosonde WMO Types are in ****green**
**The parallel is showing remarkably better biases**

## Slide 12

## Slide 13

## Monthly Averaged Height Changes(Analysis Minus Guess) at 700 hPa

**Next 2 slides show monthly averaged operational global height changes (analysis minus guess) at 700 hPa for January 2007 for 00Z, 06Z, 12Z and 18Z**
**Weaker changes in the northern hemisphere summer (not shown)**
**Of concern are the large changes from south US into Brazil**
**Height changes are mainly due to surface pressure changes**

## Slide 15

## Slide 16

## Monthly Averaged Observed SurfacePressure Biases 

**Next 4 slides show monthly average operational and parallel global observed surface pressure biases for 2-24 to 3-26, 2007 for 00Z and 12Z on a 5x5 degree for grid non gross data**
**Includes radiosonde, METAR, Synoptic and marine data – each type has similar biases**
**Need minimum count of 20 observations to plot**
**Observation minus guess in ****blue**** and analysis minus guess in ****red**
**Similar results at 06Z and 18Z (not shown)**
**The parallel biases are clearly better**

## Slide 18

## Slide 19

## Slide 20

## Slide 21

## Conclusions

**The operational GDAS has a large cold bias in the guess around 250 hPa north of the Himalayas – confirmed by different data types **
**The parallel is remarkably better**
**The operational GDAS has a large bias in the guess surface pressure from the south US into Brazil – the parallel is clearly better**