1 / 18

A simple parameterization of sea surface cooling beneath a hurricane inner core

Andrea Schumacher CIRA / CSU Mark DeMaria NOAA / NESDIS / STAR Isaac Ginis and Biju Thomas University of Rhode Island. A simple parameterization of sea surface cooling beneath a hurricane inner core. 28 th Conference on Hurricanes and Tropical Meteorology, 5/2/08. 17A.4. Outline.

yadid
Download Presentation

A simple parameterization of sea surface cooling beneath a hurricane inner core

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Andrea Schumacher CIRA / CSU Mark DeMaria NOAA / NESDIS / STAR Isaac Ginis and Biju Thomas University of Rhode Island A simple parameterization of sea surface cooling beneath a hurricane inner core 28th Conference on Hurricanes and Tropical Meteorology, 5/2/08 17A.4

  2. Outline • Motivation: hurricane-ocean feedback • Methodology & Data • Inner Core Parameters • Development of simple parameterization • Evaluation & Results • Summary & Future Work 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  3. Motivation Well observed that TCs impact upper ocean T structure Example: Cold wake (upwelling) Cold wake Rita 9/22/05 12 UTC (HWRF SST) 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  4. Motivation Also, upper ocean can have a significant impact on maintaining and/or modifying TC structure and intensity (Cione & Ulhorn, 2003) Example: SST-dependent MPI (DeMaria and Kaplan, 1994), Where T is SST, T0 is a specified reference temperature, and A, B, and C are constants. MPI = A + BC(T-T0) 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  5. Motivation Suggests Ocean / Hurricane Feedback Hurricane Surface Winds MPI Enthalpy Flux Convection ??? Upwelling ? Sea Surface Temperature 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  6. Motivation These effects most important in inner core region Cold Wake, dSST ~ 3-4º C Inner Core, dSST ~ 1 ºC Suggests Ocean / Hurricane Feedback Hurricane Surface Winds Cold wake MPI Enthalpy Flux Convection ??? Upwelling ? Inner Core Sea Surface Temperature 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  7. Cione & Ulhorn (2003) Even small dSST in the inner core region can lead to substantial changes in ocean heat content extracted and hence intensity Inner core enthalpy flux (sensible + latent), Hcore, related to upper-ocean heat content extracted by TC, QH,ext by: 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  8. Motivation (Cont…) • Forecasting TC intensity: Need to quantify dSSTIC • Very difficult to measure, sparse observations • Necessary to develop parameterization • Currently, Statistical Hurricane Intensity Prediction Scheme (SHIPS) includes a parameterization for dSSTIC • Developed from ??? • Depends on latitude, initial SST, & translational speed • Are there other storm and ocean-related parameters that should be included? 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  9. Approach • In lieu of observations, use the HWRF ocean-atmosphere coupled model fields • Explore possible statistical relationships between dSSTIC and (measurable) parameters • First step to consider a simple statistical relationship: multiple linear regression 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  10. Data • HWRF atmosphere-ocean coupled model • Grid spacing: approx. 0.19 °lon, 0.17 °lat • Domain: 98.5-50 °W, 10-47.5 °N • Reruns of named Atlantic storms from 2004-2006 • 35 of 55 named storms available in reruns • 491 forecast runs • Each run, used analysis and forecasts for t = 24, 48, 72, 96, and 120 h • Data fields used • Ocean temperature by depth • TC intensity • TC position 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  11. Parameters Only three independent parameters were considered for this preliminary study: • TC Intensity (Vmax) • Surface wind speed should directly correlate with magnitude of ocean upwelling beneath inner core • TC Translational Speed (Spd) • The more time a TC inner core spends over the same area of ocean, the more upwelling should occur • Ocean Heat Content (OHC) • The larger the ocean heat content, the deeper the ocean mixed layer, and hence the longer/stronger the upwelling needed to bring colder water to surface 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  12. OHC vs. Latitude HWRF-derived OHC 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  13. Inner Core Calculations • Inner core defined as area within 60 km radius of storm center (consistent with Cione and Ulhorn, 2003) • Averaged all points within area to calculate inner core value • If more than 10% of data points invalid (eg. over land), case not used • Data processing resulted in 1399 cases to be used in multiple regression 60 km 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  14. Regression Analysis • Dependent variable: dSSTIC = SSTIC(t=0) – SSTIC(t=t’) • All variables normalized before multiple regression • Regression coefficients: 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  15. Regression Analysis • Vmax positive  larger intensity, larger SSTIC cooling • Spd negative  faster moving, smaller SSTIC cooling • OHC negative  higher OHC, smaller SSTIC cooling 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  16. Evaluation • To test, parameterizations implemented in the SHIPS model • Run over developmental dataset (1982 – 2006) • Only times where altimetry-derived OHC available were used, 1995 – 2006 • 4 test runs • No parameterization • Current param (CP) • Linear param (LP) • Quadratic param (QP) 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  17. Evaluation (Cont…) • All parameterizations improve forecast skill after t = 24 h • CP shows greater improvement before t = 84 h • LP & QP show greater improvement at later forecast times * % forecast improvement is calculated in relation to using no dSSTIC parameterization at all in SHIPS. 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

  18. Summary / Future Work • In the HWRF model, Vmax, Spd and OHC all appear to have an impact on dSSTIC • Testing on SHIPS reanalysis data shows new parameterizations generally improve SHIPS forecast, especially at later forecast times • Current parameterization still outperforms at early forecast times  more work to be done • Physical motivation for new parameterizations is reasonable, keep working on improvements • Other parameters? • TC structure, wind radii • Thermocline depth 28th Conf on Hurricanes and Tropical Meteorology, 5.2.08

More Related