Real-Time MODIS and AVHRR Polar Winds Data Description

Period:

Real-time, with new data available as frequently as every 100 minutes. There are 13-15 datasets per day.

Coverage:

Generally poleward of +/-60 degrees latitude.

Processing:

The 1 km MODIS Level 1B HDF files are obtained through NOAA from Goddard Space Flight Center. This is sometimes referred to as the NOAA ‘bent pipe’. Two to four 5-minute granules from each orbit are remapped into a polar stereographic projection at 2 km resolution and composited using the McIDAS software. The resulting images are 2800x2800 pixels. The following figure shows the coverage from 3 granules:

MODIS winds are also generated at a number of direct broadcast (DB) sites. In addition, polar wind products are generated using AVHRR Global Area Coverage (GAC) data, and High Resolution Picture Transmission (HRPT) direct readout data. The information below applies to all products.

Winds:

Winds are derived from successive image triplets of water vapor (band 27, 6.7 μm) and the IR window channel (band 31, 11 μm). For example, from 14 passes in one day we can derive winds from 12 image triplets. At present, day boundaries are not crossed. The NOGAPS model data is used as a first guess. There are approximately 25,000 quality-controlled vectors per day at each pole.

Wind Data Files at CIMSS:

Wind data files are available at CIMSS and at NOAA NESDIS. For most purposes we recommend obtaining the data files from the NESDIS server, described in the next section. At CIMSS we have both the McIDAS MD file format and text file format. The NESDIS files are in BUFR format. The CIMSS files can downloaded via anonymous ftp from:

ftp.ssec.wisc.edu

in the /velden/winds/terra and /velden/winds/aqua directories.

The files are organized by wind set number. Since there are 14-15 orbits/day, we get 12-13 wind sets/day (overlapping triplets, but not crossing the day boundary). If wind sets are reprocessed, the files are overwritten.

Text Files

The text files are named:

QIyyyyddd.nn.pp.gz

where

yyyy = year

ddd = day of year

nn = 01 to 13 indicating wind set of the day

pp = NP or SP indicating north or south pole

For example:

QI2002183.01.NP.gz

Is the first wind set from day 2002183 over the North Pole.

The data contained in the text file are of the form:

type sat day hms lat lon pre spd dir rff qi temp

WV MODIS 20021113 1530 82.78 -101.92 450 19.8 164 59.25 .83 234.6

WV MODIS 20021113 1530 86.73 -127.92 450 24.0 220 73.81 .71 235.7

WV MODIS 20021113 1530 82.24 -98.92 462 14.9 153 54.79 .83 234.6

type: WV - water vapor (6.7 μm); IR - infrared (11 μm)

sat: MODIS [all from MODIS instrument]

day: yyyymmdd: yyyy - year, mm - month of year; dd - day of month

hms: hhmm: hour and minute of the middle image [GMT]

lat: latitude (positive North)

lon: longitude (positive West) Note: East longitudes are negative.

pre: pressure level of wind [hPa]

spd: wind speed in m/s

dir: wind direction

rff: CIMSS recursive filter quality control value

qi: EUMETSAT control value

temp: IR or WV brightness temperature

McIDAS MD Files

The MD files are named:

MDXXxxnn.yyyyddd.pp.gz

where:

xxnn = 2001 to 2013 [NP]

xxnn = 2101 to 2113 [SP]

and the last 2 digits are the wind set number as above.

For example: MDXX2001.2002183.NP.gz is the first wind set from day 2002183 over the North Pole.

BUFR Files

The MODIS direct broadcast and AVHRR winds are also available in BUFR format. The MODIS bent pipe winds are not available in BUFR. Standard BUFR decoders may work. Our BUFR decoder is available via anonymous FTP from

stratus.ssec.wisc.edu

in the /pub/winds/bufr_software directory. Pre-compiled versions for Linux, Mac OS X, and Windows are available.

Wind Data Files at NESDIS:

MODIS bent pipe wind products are available at CIMSS and at NOAA NESDIS. For most purposes we recommend obtaining the data files from the NESDIS server. The NESDIS files are in BUFR format.

NESDIS Anonymous Server: gp16.ssd.nesdis.noaa.gov

Directory: /pub/bufr/modis_winds

Dataset Naming Convention:

Aqua Files: satwnd.bufrxxxx.aqua.Dyyddd.Thh:mm:ssZ

Terra Files: satwnd.bufrxxxx.terra.Dyyddd.Thh:mm:ssZ

where:

xxxx = cdft for IR cloud-drift winds

xxxx = wvap for water vapor winds

yy = year

ddd = julian day

hh,mm,ss = hour, minute, second (system time)

Usage Policy:

The data are free, where "free" means that they are available at no cost. "Free" does not mean unconditional use. In order to ensure that they are being used as intended, please send us a note with a brief description of your application. While we have tried to make clear their limitations, there will almost certainly be some applications that we have not addressed, and for which the data or programs are not well-suited. Additionally, if these data will play a significant role in a journal publication, please consider including the developers as co-authors.

Contacts:

If you have any questions about the data or project, contact:

Dave Santek: dave.santek@ssec.wisc.edu

Jeff Key: jeff.key@ssec.wisc.edu

Chris Velden: chris.velden@ssec.wisc.edu