# Presentation: 710684

## Polar Winds from Satellite Imagers and Sounders

**Polar Winds from Satellite Imagers and Sounders**

- Jeffrey Key1, David Santek2, Christopher Velden2, Lars Peter Riishojgaard3, Cheng-Zhi Zou1, Mark DeMaria1, Jennifer Francis4, and Mike Van Woert1
-  1Office of Research and Applications, NOAA/NESDIS
- 2Cooperative Institute for Meteorological Satellite Studies (CIMSS),  Madison
- 3NASA Global Modeling and Assimilation Office
- 4Rutgers University* *

## Sparse Observation Network

- Raob locations are indicated by their WMO station numbers.

**Arctic and Antarctic Rawinsonde Distribution**

**Sparse Observation Network**

## Model Wind Errors

- Francis, 2002 (GRL) examined differences between NCEP/NCAR and ECMWF Reanalysis winds and raob winds for raobs that were not assimilated in the reanalysis, from the LeadEx (1992) and CEAREX (1988) experiments.
- It was found that both reanalyses exhibit large biases in zonal and meridional wind components, being too westerly and too northerly.  Winds are too strong by 25-65%.

## Geostationary Cloud Motion Vectors

- Five geos provide coverage for winds in the tropics and mid-latitudes. However, the total number of wind vectors drops off steadily beyond a 30 degree view angle, with a sharp drop off beyond 60 degrees. The success rate (#vectors/total possible) drops off beyond 50 degrees. Winds from polar orbiters can help fill the high-latitude areas between geos where view angles are large.

**Notes:**
Winds from five geos are being processed every six hours to produce vectors of comparable accuracy (hi winds compare within 7 m/s of raobs); GOES and Meteosat winds are being produced every three hours on most days.

## Orbits

*Figures from http://www.rap.ucar.edu/~djohnson/satellite/coverage.html*

**Orbits**

## One Day of Arctic Orbits

- MODIS band 27 (6.7 m)

## Unlike geostationary satellites at lower latitudes, it is not be possible to obtain complete polar coverage at a snapshot in time with one or two polar-orbiters.  Instead, winds must be derived for areas that are covered by two or three successive orbits, an example of which is shown here.  The whitish area is the overlap between three orbits.

## Infrared Winds

**Infrared Winds**

- 05 March 2001: Daily composite of 11 micron MODIS data over half of the Arctic region. Winds were derived over a period of 12 hours. There are about 4,500 vectors in the image. Vector colors indicate pressure level - yellow: below 700 hPa, cyan: 400-700 hPa, purple: above 400 hPa.

**Low  Level**
**Mid  Level**
**High Level**

## Water Vapor Winds

**Water Vapor Winds**

- 05 March 2001: Daily composite of 6.7 micron MODIS data over half of the Arctic region. Winds were derived over a period of 12 hours. There are about 13,000 vectors in the image. Vector colors indicate pressure level - yellow: below 700 hPa, cyan: 400-700 hPa, purple: above 400 hPa.

**Low  Level**
**Mid  Level**
**High Level**

## One Day of Arctic Orbits

- MODIS band 27 (6.7 m)

## Near Real-Time Winds Examples

- MODIS

- AVHRR

## Aqua MODIS Data Acquisition Delays

- The figures above show the time delay in the availability of Aqua MODIS data, where the delay is the time between the image time and the time a granule is available on the NOAA “bent pipe”.  This histogram of time delays is for the south polar region.

## Terra MODIS Data Acquisition Delays

- The figures above show the time delay in the availability of Terra MODIS data, where the delay is the time between the image time and the time a granule is available on the NOAA “bent pipe”.  This histogram of time delays is for the south polar region.

## MODIS Polar Winds Real-Time Processing Delays

- Relative to Two ECMWF Processing Cycles

- The blue points represent winds that will be included in the 12Z run; the black points represent winds that will be used in the 0Z run.  The green points will not be used in either, as a result of the processing delay. The 12Z run is not done until 19Z; the 0Z run is done at 9Z.

- 1-3 hrs before MODIS data is available + 1/5 hr to transfer data from GSFC to CIMSS + 1 hr to process winds + 1-1/2 hrs offset because we assign vector time to middle image = 3-6 hours total time

- Frequency of Delays in Wind Retrievals

## Overpass Frequency

**Overpass Frequency**

## Model Impact Studies

## DAO Model Impact Studies: Arctic and Antarctic

- Forecast scores (anomaly correlations) as a function of forecast range for the 500 hPa geopotential over the Arctic (left) and Antarctic (right).  The anomaly correlation is the correlation between the forecast geopotential height anomalies, with and without the MODIS winds, and ECMWF analyses. The Arctic and Antarctic are defined as poleward of 60 degrees latitude.
- Over the Arctic the forecast impact is positive.  Over the Antarctic the impact is neutral to positive.

**Notes:**
Due to the lack of independent observations especially in the southern hemisphere, the so-called self-validation method - in which the verifying analysis for a given forecast is taken from the same assimilation run from which the forecast was launched – is somewhat problematic. Essentially, a high-latitude analysis with few observations would be very similar to the forecast and the forecast could therefore have high skill scores without necessarily being close to the actual evolution of the atmosphere. This would put the MODIS forecasts at a disadvantage. In order to provide a modicum of external validation as well as to be able to extend the validation period beyond the length of the MODIS period itself, both sets of forecasts were therefore verified against operational ECMWF analyses rather than their own analyses. 

The forecasts from the MODIS assimilation scored significantly higher in the Northern Hemisphere, and marginally higher in the southern hemisphere. It should be noted that the skill scores shown are calculated for the high-latitude regions only, due to the general lack of observations over Antarctica, the southern hemisphere result is therefore probably less significant that the one for the northern hemisphere. Calculated over the entire extratropics of each hemisphere (next slide), the MODIS winds improved the skill in the northern hemisphere, whereas the southern hemisphere impact was neutral.

## Forecast Busts (GMAO)

**Forecast Busts (GMAO)**

- Arctic

- Southern Hemisphere Extratropics

- Blue is forecast with MODIS winds; red is control run

## ECMWF Model Impact: Arctic

- 1000 hPa

- Forecast scores (anomaly correlations) as a function of forecast range for the geopotential at 1000 hPa (left) and 500 hPa (right).  Study period is 5-29 March 2001.  Forecast scores are the correlation between the forecast geopotential height anomalies, with and without the MODIS winds, and their own analyses. The Arctic (“N. Pole”) is defined as north of 65 degrees latitude.
- There is a significant positive impact on forecasts of the geopotential from the assimilation of MODIS winds, particularly for the Arctic. Forecast accuracy is extended by about 5 hrs.

- 500 hPa

**Notes:**
For most levels and regions the NRMSVD and speed bias are similar or slightly poorer compared to other extra-tropical AMVs currently assimilated by ECMWF.  The highlights the acceptable quality of the MODIS winds.  The current exception is at lower and medium levels in the Antarctic, which have larger NRMSVDs and speed biases. 

Globally, the fit of other observations against the FG or the analysis is not significantly altered when MODIS winds are assimilated.  The fit of winds from raobs, pilot reports, or other aircraft observations is virtually unaltered for the Arctic.  The lack of change of the FG fit to other observations suggests that the MODIS winds do not disagree with the rest of the observing network in the Arctic and is thus a positive aspect.  The degradation of the FG fit against raobs in the Antarctic suggests some disagreement between the MODIS winds and raob winds, at least in the coastal areas where most of the radiosondes are located.  It was worse before additional restrictions were placed on lower level AMVs over ice and high orography.  Also, in such conditions the vertical and horizontal resolution of the forecast fields used for height assignment are likely to play a particularly important role.

The forecasts from the MODIS and CTL experiments are each validated against their own verifying analyses.  The verifying analysis is a forecast but with observations (surface, raob, satellite, etc.) filtered in (at the end or throughout?) to bring the forecast closer to truth.  The control run is strictly a forecast.

## ECMWF Model Impact: Northern Hemisphere

- 1000 hPa

- Forecast scores (anomaly correlations) as a function of forecast range for the geopotential at 1000 hPa (left) and 500 hPa (right).  Study period is 5-29 March 2001. Forecast scores are the correlation between the forecast geopotential height anomalies, with and without the MODIS winds, and their own analyses.  The Northern Hemisphere is defined as north of 20 degrees latitude.
- The improvements for the Northern Hemisphere are significant at the 2% or better level (t-test) for the forecast range of 2-5 days at most levels.

- 500 hPa

**Notes:**
The verifying analysis is a forecast but with observations (surface, raob, satellite, etc.) filtered in (at the end or throughout?) to bring the forecast closer to truth.  The control run is strictly a forecast.

## ECMWF: Error Propagation to the Midlatitudes

- This animation illustrates the propagation of analysis errors from the poles to the midlatitudes for one case study.  Each frame shows the 500 hPa geopotential height for forecasts from 1 to 5 days in 1 day  increments.  The solid blue line is the geopotential from the experiment that included MODIS winds;  the **dashed black line** is the control (CTL) experiment without MODIS winds.  Solid red lines show positive differences in the geopotential height (MODIS minus CTL), and **thick dashed green lines** show negative differences.
- The area of large positive differences near the  Beaufort Sea (north of Alaska) moves southward over the 5-day period.  The CTL run is forming a deeper trough over central Alaska and then over the Pacific south of Alaska than the MODIS run.
- The 5-day MODIS forecast verifies better against the subsequent analysis (not shown), so the initial analysis for this MODIS forecast was closer to the “truth” than the CTL (positive impact on forecast).  The propagation of differences is therefore also a propagation of analysis errors in the CTL forecast.
**Better observations over the poles should improve forecasts in the midlatitudes.**

## Error Propagation to the Midlatitudes: Snowfall

- Accumulated snowfall forecasts (mm water equivalent) over Alaska for 03/20/02 (end of animation period).  At right is the snowfall from the 5-day CTL forecast, below left is the snowfall from the 5-day MODIS forecast, below right is the snowfall from a 12-hr forecast for verification.  The MODIS run verified better, and the CTL run produced spurious snowfall in southern Alaska.

**Notes:**
The upper left panel shows the 96-108h forecast of 12h accumulated snow (in mm water equivalents) for the CTL forecast from 15 March 12Z. The upper right panel shows the same forecast from the MODIS experiment. The lower panel shows the 0-12h forecast of 12h accumulated snow from the 19 March 12Z forecast - as a proxy verifying snow analysis. As you see, CTL shows some spurious snow fall in Southern Alaska, whereas MODIS doesn't. And MODIS "verifies" much better.

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## Slide 24

## Plans