Quantification and Exploration of Diurnal Oscillations in Tropical Cyclones

Details

• Journal Title:
  Monthly Weather Review
• Personal Author:
  Knaff, John A. ; Slocum, Christopher J. ; Musgrave, Kate D.
• NOAA Program & Office:
  NESDIS (National Environmental Satellite, Data, and Information Service) ; CIRA (Cooperative Institute for Research in the Atmosphere) ; STAR (Center for Satellite Applications and Research)
• Description:
  Diurnal oscillations of infrared cloud-top brightness temperatures (Tbs) in tropical cyclones (TCs) as inferred from storm-centered, direction-relative longwave infrared (~11 μm) imagery are quantified for Northern Hemisphere TCs (2005–15) using statistical methods. These methods show that 45%, 54%, and 61% of at least tropical storm-, hurricane-, and major hurricane-strength TC cases have moderate or strong diurnal signals. Principal component analysis–based average behavior of all TCs with intensities of 34 kt (17.5 m s−1) or greater is shown to have a nearly symmetric diurnal signal where Tbs oscillate from warm to cold and cold to warm within and outside of a radius of approximately 220 km, with maximum central cooling occurring in the early morning (0300–0800 local standard time), and a nearly simultaneous maximum warming occurring near the 500-km radius—a radial standing wave with a node near 220-km radius. Amplitude and phase of these diurnal oscillations are quantified for individual 24-h periods (or cases) relative to the mean oscillation. Details of the diurnal behavior of TCs are used to examine preferred storm and environmental characteristics using a combination of spatial, composite, and regression analyses. Results suggest that diurnal, cloud-top Tb oscillations in TCs are strongest and most regular when storm characteristics (e.g., intensity and motion) and environmental conditions (e.g., vertical wind shear and low-level temperature advection) support azimuthally symmetric storm structures and when surrounding mid- and upper-level relative humidity values are greater. Finally, it is hypothesized that larger mid- and upper-level relative humidity values are necessary ingredients for robust, large-amplitude, and regular diurnal oscillations of Tbs in TCs.
• Keywords:
  Atmospheric Science
• Source:
  Monthly Weather Review, 147(6), 2105-2121
• DOI:
  https://doi.org/10.1175/mwr-d-18-0379.1
• ISSN:
  0027-0644 ; 1520-0493
• Format:
  PDF
• Publisher:
  American Meteorological Society
• Document Type:
  Journal Article
• Funding:
  Grant no. NA17RJ1228
• Rights Information:
  Other
• Compliance:
  Library
• Main Document Checksum:
  urn:sha-512:1dd29a7dd8dfbe1fd1c951bc49f698d55178f72b980832747f24db9469e73f3d8f00ee436c7475fb11f22f6ce5c04db910e18903d0ac6aa183fdda65faea7045
• Download URL:
  https://repository.library.noaa.gov/view/noaa/59881/noaa_59881_DS1.pdf
• File Type:
  [PDF - 2.24 MB ]