# Presentation: 915656

## Polar Winds from Satellite Imagers and Sounders

**Polar Winds from Satellite Imagers and Sounders**

- MODIS Winds Group:
- Jeff Key1, David Santek2, Christopher Velden2, Lars Peter Riishojgaard3, Paul Menzel1
- Sounder Winds Group:
- Cheng-Zhi Zou1, Mark DeMaria1, and Jennifer Francis4
-  1Center for Satellite Research and Applications, NOAA/NESDIS
- 2Cooperative Institute for Meteorological Satellite Studies (CIMSS),  Madison
- 3NASA Global Modeling and Assimilation Office
- 4Rutgers University* *

## MODIS winds filling observing system void

- Being used operationally since Jan 2003

## MODIS Polar Winds

- North Atlantic

- Europe

- ECMWF pre-op tests in 2002

- 500 hPa geo potential

**MODIS Polar Winds**

## Forecast Busts (GMAO)

**Forecast Busts (GMAO)**

- Arctic

- Southern Hemisphere Extratropics

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

## FREQUENCY OF SUPERIOR HURRICANE PERFORMANCE (%)*  

| 13.2  | 43.6 | 66.5 | 94.9 | 102.8 | 157.1 | 227.9 | 301.1 | Cntrl |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 11.4 | 34.8 | 60.4 | 82.6 | 89.0 | 135.3 | 183.0 | 252.0 | Cntrl + MODIS |
| 74 | 68 | 64 | 61 | 52 | 46 | 39 | 34 | Cases   (#) |
| 00-h | 12-h | 24-h | 36-h | 48-h | 72-h | 96-h | 120-h | Time |

**AVERAGE HURRICANE TRACK ERRORS (NM) **

| 48.9   | 31.0 | 44.8 | 36.5 | 39.6 | 39.1 | 28.2 | 29.4
 | Cntrl |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 51.1 | 69.0 | 55.2 | 63.5 | 60.4 | 60.9 | 71.8 | 70.6 | Cntrl + MODIS |
| 74 | 68 | 64 | 61 | 52 | 46 | 39 | 34 | Cases   (#) |
| 00-h | 12-h | 24-h | 36-h | 48-h | 72-h | 96-h | 120-h | Time |

**FREQUENCY OF SUPERIOR HURRICANE PERFORMANCE (%)*****  **

- Percent of cases where the specified run had a more accurate hurricane position than the other run.
- Note: These cases are for hurricanes in the subtropics.

## MODIS Winds in NWP

## The Global Impact of MODIS-Derived Polar Winds in Model Forecasts

- David Santek

- What are possible explanations for the **global** impact of **polar** wind data? Two areas are being investigated:
- 1) 3DVAR assimilation
- 2) Dynamics near the jet stream

## 3DVAR Effects

**3DVAR Effects**

- Wind speed difference between GFS model runs with and without the MODIS winds at 800 hPa. Yellow is close to zero difference; brown to black is up to a +7 m/s difference; green to blue is –1 to –6 m/s difference. Results are based on analyses, not forecasts.

- 24 hours into experiment

- 6 days into experiment

**Notes:**
The MODIS winds are being assimilated using either 3DVAR or 4DVAR, depending on the model. An experiment was run from 10 August through 30 September 2004 using a pre-operational version of the GFS. Analyses and forecast output from the control and continuously-assimilated MODIS winds model runs were used. This system uses 3DVAR for data assimilation. The nature of 3DVAR assimilation results in global adjustments, especially in data void regions. 
The figures show wind speed difference at 800 hPa between the control and MODIS winds model runs. The colors range from black +7 m/s (MODIS winds have an effect to increase the winds speeds) to light blue -6 m/s (MODIS winds decrease the winds speeds). The figure on the left is from only 24 hours into the experiment, on 11 Aug 2004. These are analyses, not forecasts. It is not physically possible for upper-tropospheric polar winds, poleward of 65 degrees latitude, to have an impact on lower-tropospheric winds in the tropics in only 24 hrs, so the large differences are probably due to adjustments by the 3DVAR assimilation, which propagate throughout the global domain. Note, there are little differences over continents, where RAOBS are weighted higher. The figure on the right is 6 days into the experiment; similar types of differences can be seen.

## Dynamics near the Jet Stream

**Dynamics near the Jet Stream**

## Wind Differences

- Geostrophic difference

**Wind Differences**

- Differences between the control and MODIS winds model runs for the 500 hPa geostrophic and ageostrophic winds.

- Ageostrophic difference

**Notes:**
Vector wind differences (not simply wind speed diffs, so they’re all positive) in the 500 hPa geostrophic and ageostrophic winds between the control and MODIS winds analyses at 00Z on 11 September 2004. The geostrophic winds is computed from the height fields from both the control and MODIS winds model analyses and runs. The ageostrophic winds are the geostrophic winds minus the model U & V fields (the “real” wind). There are 2 main areas where the differences are large in both the geostrophic and ageostrophic fields: Just south of the Kamchatka peninsula in eastern Russia and south of the Gulf of Alaska. These regions are poleward of, or very near, the polar jet stream. The polar winds are derived no further south than Alaska, so the differences near the jet stream represent a mass adjustment by the 3DVAR, but due to the dynamics near the jet stream, this is like a barrier (note Palmen and Newton vertical cross section in upper right). There are some other differences in the lower left corner; this is in a data void region and probably represent a cumulative effect of assimilating the MODIS winds.

## 1000-500 hPa Thickness Differences

**1000-500 hPa Thickness Differences**

- 1000-500 hPa thickness difference between control and MODIS winds analyses. The range from blue to red is from -30 to +30 gpm difference. 500 hPa height contours in black. White shading indicates 30 m/s wind speed.

**Notes:**
The large geostrophic and ageostropic wind differences from the previous slide are located in a couple of short waves in the jet that extends across the north Pacific. These are also areas where the thickness difference is shaded blue, indicating that the MODIS winds have an effect of cooling the layer. The range from blue to red is from -30 to +30 gpm difference. The 500 hPa contours are from the assimilation using MODIS winds.
We are seeing differences of about the same magnitude, 2-3 m/s, in the geostrophic and ageostrophic winds....sometimes at coincident locations.  The assimilation of the winds result in a change in the mass, thereby changing the height field (the geostrophic wind). Additionally, there is a change in the ageostrophic winds. The ageostrophic wind points to the left of the geostrophic acceleration. There may be acceleration due to curvature in these shortwaves, and a change in the ageostrophic wind may reflect changes in these accelerations. Part of the problem with drawing a conclusion is that the MODIS winds are measured quite some distance from where we see the impact near the jet. It may be more than a coincidence that the biggest impact is in the shortwaves. In assimilating the winds by forcing a mass balance, these small vorticity features are disrupted more than winds in a zonal flow.

## Effects into the Mid- and Low-Latitudes

**Effects into the Mid- and Low-Latitudes**

- Forecast out 5 days in 6-hour increments.

- HurricaneIvan

**Notes:**
Same parameters as previous figure, but this is a depiction of the forecast fields out to 5 days, in 6-hour steps. The differences in the thickness fields grow over the 5 days, primarily in and around the jet. The alternating red and blue regions in the later forecast time represent a changing phase in the waves between the control and the forecast containing the MODIS winds: the red over the north central US is the region where the MODIS winds have slowed the advance of the ridge, the blue over the plains is where the trough is also slowed. The alternating pattern along the jet suggests the MODIS winds have slowed the progression of all waves in the jet stream region. These effects are felt into mid-latitudes as the trough digs into the plains. The small cyclone crossing Cuba into Florida is the forecast of hurricane Ivan, which eventually hit Gulf Shores Alabama. Many times the timing of a trough can affect when and where a Gulf of Mexico hurricane will make a turn more northward. In this case, the forecast differs more in the later time periods, represented by the separating red and blue blobs. The slowing of the overall wave pattern in the MODIS winds run allows the hurricane to stay further west.

## Direct Broadcast MODIS Polar Winds

- MODIS winds do not meet 3 hr cut-offs of most regional/limited area data assimilation systems.  Possible solution: generate winds at high-latitude direct broadcast stations.
-  Northern Hemisphere - Fairbanks (NOAA); Tromsø, Norway (Ksat); Soldankylä, Finland (FMI)
-  Southern Hemisphere **- McMurdo, Antarctica (NSF; operational)**; Troll, Antarctica (Norway)
- See the poster!

**Notes:**
The figures show the distribution of time that it takes to generate the winds, including MODIS data acquisition.  The left figure is for the Arctic; the right is for the Antarctic. It is not yet known how much time we can save by using DB sites, but we hope it will be at least 30-45 minutes.

## Sounder Winds

**Sounder Winds**

- TOVS Winds Over the Arctic

## The next version will combine TOVS thermal winds and AVHRR feature-tracked winds.

## Wind Retrievals from AMSUMark DeMaria and Jack Dostalek

- AMSU-derived 500-hPa heights and geostrophic winds for 0015 UTC 17 December 2004.

- GFS analysis of 500-hPa heights and geostrophic winds for 0000 UTC 17 December 2004.

**Wind Retrievals from AMSU**Mark DeMaria and Jack Dostalek

**Notes:**
Wind Retrievals over the Arctic:  Using a method originally developed for use with tropical cyclones, a wind retrieval technique using vertical temperature profiles derived from Advanced Microwave Sounding Unit (AMSU) radiances is being developed for the polar regions.  With a boundary condition given by a 100-hPa height field from the Global Forecast System (GFS) analysis, the temperature profiles are used in the downward integration of the hydrostatic equation to compute height as a function of pressure.  A balance condition is then applied to compute the stream function, from which the u- and v-component of the non-divergent wind can be evaluated.  The left figure shows the 500-hPa height field and the geostrophic winds as calculated using the technique applied to AMSU data from 0015 UTC 17 December 2004.  For comparison, the 0000 UTC 17 December 2004 500-hPa heights and geostrophic winds from the GFS analysis are given in the plot on the right.  The retrieval technique captures the overall pattern quite well, although there is a negative height bias of 28 m.  Future work will include using a nonlinear balance equation to derive the stream function, as well as validation against collocated radiosonde data.

The nonlinear balance equation will probably give slightly more accurate results in regions with high curvature. For purely circular flow, the nonlinear balance winds are the same as the gradient winds. Thus, whenever the V**2/r term becomes important relative to fV and the pressure gradient, the nonlinear balance winds should be better. However, both the geostrophic winds and the nonlinear balance winds are non-divergent. We would have to solve a secondary circulation equation for the divergent component. That would be the classical omega equation for the geostrophic case, and something more messy for the nonlinear balance winds. 

## Summary

- The MODIS winds retrieval method continues to be refined.  A parallax correction is being tested, and Terra and Aqua MODIS data streams will be combined.
- The MODIS winds are used operationally by seven NWP centers in four countries.
- MODIS winds are also calculated at the McMurdo, Antarctica DB site, with more sites to come.
- Methods to calculate thermal winds from sounders are being refined.  Case studies have been performed with AMSU.  TOVS winds have been calculated for a 20+ year period.
- MODIS winds will be used as a boundary condition in the AIRS thermal wind approach (Cheng-Zhi Zou and Weizhong Zheng).
- Historical AVHRR winds are being merged with TOVS winds.

## Supplemental Slides     

## Progress in Sounder Wind Profile Retrievals Using 

**MODIS Winds as Boundary Conditions**
- Cheng-Zhi Zou and Weizhong Zheng
** **
*** ***
***        ***

- Algorithm utilizes the thermal wind relationship plus the University of Washington Planetary Boundary Layer Model (UWPBL 4.1).
- Boundary conditions set up near mid-troposphere to use any wind source. Future studies will use MODIS winds and AIRS temperature retrievals as inputs to derive satellite wind profiles.
- Derive first-guess atmospheric wind profiles including surface winds.
- Lagrange multipliers in a variational formalism are then used to force the first-guess wind to conserve mass.

##    Comparison of Surface Winds over the Polar Region

**   ****Comparison of Surface Winds over the Polar Region**

**Notes:**
Case:   July 2005.
Data:   (1) Temperature profiles from NCEP Final (FNL) Analysis with 1x1° resolution as inputs.
               (2) Wind at 450 mb from FNL analysis as boundary conditions. 
Comparison between FNL surface winds and derived surface winds.

##                      Statistics for 13 Radiosonde Stations

**Notes:**
13 radiosonde observations around the Antarctic coast.  Note that the FNL winds are ‘assimilated winds’ where radiosonde data have been assimilated into the FNL. So the derived winds have good accuracy compared to the assimilated winds.