An analysis of intensity estimates of the advanced microwave sounding unit amsu 2005 2007
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An Analysis of Intensity Estimates of the Advanced Microwave Sounding Unit (AMSU), 2005-2007. Corey Walton NHC SCEP Intern August 7, 2008. Purpose. To provide information on the accuracy of the AMSU method of estimating tropical cyclone intensity for the 2005 to 2007 hurricane seasons.

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An analysis of intensity estimates of the advanced microwave sounding unit amsu 2005 2007

An Analysis of Intensity Estimates of the Advanced Microwave Sounding Unit (AMSU), 2005-2007

Corey Walton

NHC SCEP Intern

August 7, 2008


Purpose
Purpose Sounding Unit (AMSU), 2005-2007

  • To provide information on the accuracy of the AMSU method of estimating tropical cyclone intensity for the 2005 to 2007 hurricane seasons.

  • To compare the AMSU method with the Dvorak method (TAFB/SAB) for the 2005 through 2007 hurricane seasons when aircraft reconnaissance is available.


General overview
General Overview Sounding Unit (AMSU), 2005-2007

  • Used ATCF database for all data retrieval

  • Includes both the Atlantic Basin and the Eastern Pacific Basin

  • Data points require reconnaissance flight data within 2 hrs of the time the AMSU data was taken

  • Wind estimate comparisons only (kts)

  • Used both CIMSS and CIRA AMSU real time estimates and the TAFB and SAB Dvorak estimates


Amsu in general
AMSU (in general) Sounding Unit (AMSU), 2005-2007

  • Microwave sounder which includes channels for measuring brightness temperatures (Tb)

  • AMSU-A (temperature, 15 channels) and AMSU-B (moisture, 5 channels) 1998-present

  • Resolution: ~50km at nadir, ~100 km at limb

  • Temperature anomaly directly related to TC intensity / size (completely independent of Dvorak)

  • No dependence on previous estimate

-Used with permission of Derrick Herndon


Cimss vs cira

CIMSS Sounding Unit (AMSU), 2005-2007

AMSU-A channels 5-8

AMSU-B channel 16

Corrections applied to account for sub-sampling and scan geometry.

Uses only TC data within 6 hours of recon

Depends on RMW and P_env

Uses multiple regression scheme directly from AMSU channels to get MSLP

MSLP used to get corresponding MSW

Updated annually

CIRA

AMSU-A, 23 pressure levels

No sub-sampling correction for resolution

Uses any best track data for regression

Relies on model data for boundary conditions

Uses AMSU channels to get temperature and wind fields and then multiple regression scheme to get MSLP and MSW separately

Known to work well in higher latitudes

Last update in 2005

CIMSS vs. CIRA

-Used with permission of Derrick Herndon


Data division overview
Data Division Overview Sounding Unit (AMSU), 2005-2007

  • Subdivided by Year (2005,2006,2007)

    • Subdivided by homogeneity*

  • Combined Data (all years 2005-2007)

    • Subdivided by homogeneity*

    • Subdivided by intensity

    • Subdivided by size

      *Homogeneity is determined by having all values (CIMSS, CIRA, TAFB, SAB) for a single time. Also divided by being homogeneous for only AMSU or Dvorak.


Sample data set
Sample Data Set Sounding Unit (AMSU), 2005-2007


2005 findings
2005 Findings Sounding Unit (AMSU), 2005-2007

  • Season Notes

  • Most active year in history (28 total storms)

  • 7 major hurricanes: Dennis(4), Emily(5), Katrina(5), Maria(3), Rita(5), Wilma(5), Beta(3)

  • Data Set includes these storms: Arlene, Bret, Cindy, Dennis, Emily, Franklin, Harvey, Irene, Jose, Katrina, Ophelia, Philippe, Rita, Stan, Tammy, Wilma, Beta, Gamma

2005 Track Map


2005 findings graphs
2005 Findings-Graphs Sounding Unit (AMSU), 2005-2007


2006 findings
2006 Findings Sounding Unit (AMSU), 2005-2007

  • Season Notes

  • Season less active than anticipated

  • Total of 10 storms (AT), with 2 major hurricanes (Gordon and Helene)

  • Data Set includes these storms: Chris, Ernesto, Florence, Gordon, Helene, John (EP), Lane (EP)

2006 Track Map


2006 findings graphs
2006 Findings- Graphs Sounding Unit (AMSU), 2005-2007


2007 findings
2007 Findings Sounding Unit (AMSU), 2005-2007

  • Season Notes

  • Total of 15 tropical cyclones, including 2 major hurricanes, both Cat 5 (Dean and Felix)

  • Data Set includes these storms: Andrea, Barry, Dean, Erin, Felix, Gabrielle, Humberto, Ingrid, Lorenzo, Noel

2007 Track Map


2007 findings graphs
2007 Findings-Graphs Sounding Unit (AMSU), 2005-2007


Combined findings 2005 2007
Combined Sounding Unit (AMSU), 2005-2007Findings (2005-2007)

  • Notes

  • Distribution of data set:

  • 2005: 68 data values

  • 2006: 33 data values

  • 2007: 27 data values

  • Data set from a total of 35 tropical cyclones, including 10 major hurricanes


Combined findings 2005 20071
Combined Findings (2005-2007) Sounding Unit (AMSU), 2005-2007


Comparison to previous studies
Comparison to Previous Studies Sounding Unit (AMSU), 2005-2007


Intensity subdivision findings
Intensity Subdivision Findings Sounding Unit (AMSU), 2005-2007

  • Divided into three groups:

    • Tropical Depressions and Tropical Storms

    • Category 1 and 2 Hurricanes

    • Category 3, 4 and 5 Hurricanes


Intensity findings 2005 2007
Intensity Findings (2005-2007) Sounding Unit (AMSU), 2005-2007


Size subdivision findings
Size Subdivision Findings Sounding Unit (AMSU), 2005-2007

  • Size determined by Radius of Max Wind (RMW)

  • Divided into three categories:

    • Small: RMW 5-15 nm

    • Medium : RMW 20-30 nm

    • Large: RMW 35+ nm


Size findings 2005 2007
Size Findings (2005-2007) Sounding Unit (AMSU), 2005-2007


Conclusions
Conclusions Sounding Unit (AMSU), 2005-2007

  • CIMSS AMSU more reliable than CIRA in most cases

  • Overall, CIMSS AMSU is competitive with Dvorak for 2005-2007 hurricane seasons

  • Both CIMSS and CIRA AMSU are competitive with Dvorak for storms with an RMW of 20 nm and greater and outperforms Dvorak for storms with an RMW of 30 nm and greater

  • CIRA AMSU is competitive with Dvorak for TD’s and TS’s

  • CIMSS AMSU outperforms Dvorak for TD’s and TS’s


For the future
For the Future Sounding Unit (AMSU), 2005-2007

  • In process of obtaining confidence levels for all AMSU cases (help to remove outliers when confidence not high)

  • Stratify by storm latitude and evaluate statistics

  • Add ADT values for comparison

  • Will add 2008 TC’s to database and will reevaluate statistics after the season

  • The AMSU techniques (esp CIMSS) undergoes revisions which will need to be evaluated

  • Evaluate AMSU 34 kt wind radii technique from CIRA


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