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Investigation of meso-scale atmospheric phenomena in the marine boundary layer using multi-sensor satellite data.

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  1. Investigation of meso-scale atmospheric phenomena in the marine boundary layer using multi-sensor satellite data • Werner Alpers Institute of Oceanography University of Hamburg Hamburg, Germany • …...

  2. Examples of mesoscale atmospheric phenomena: • Coastal atmospheric fronts in Asian Marginal Seas • Katabatic winds • Atmospheric gravity waves • Gap winds • Bora winds • Atmospheric boundary layer rolls

  3. Coastal fronts off the east coast of Taiwan ERS-2 SAR, 18 Jan. 1999 ERS-1 SAR, 7 April 1996 ERS-2 SAR 24 Nov.1997 Envisat ASAR, WS 8 Nov. 2006

  4. Question: Are these frontal features really sea surface signatures of atmospheric fronts or of the Kuroshio front? Answer: Yes, they are!

  5. The 18 Jan. 1999 front Rain cells ERS-2 SAR, 18 Jan. 1999, 02:24 UTC The radiosonde at Hualien measured a humidity that varied between 86% and 100 % Imaged area: 380 km x 100 km

  6. Cloud image obtained by the Japanese Geostationary Meteorological Satellite GMS-4 in the visible band.

  7. Surface weather map of 18 January 1999 at 0:00 UTC (8:00 LT) Air temperature at Hualien (sea level): 16.7 degr C

  8. Theories on the formation of the atmospheric front: 1) Katabatic wind

  9. Simulations carried out with the MM5 model Wind velocity (vectors) and wind speed (color) Vertically integrated cloud water J.- P, Chen of the National Taiwan University; Taipei

  10. Streamlines and cloud water distribution along the profile shown in the previous slide

  11. Envisat ASAR WS image 8 Nov. 2006 at 01:50 UTC Wind field derived from this ASAR image by using the wind direction from the NCEP model The 8 Nov. 2006 atmospheric front

  12. The 8 Nov. 06 atmospheric front MODIS Terra image (visible composite) acquired on 8 November 2006 at 02:30 UTC Wind field calculated with the MM5 model

  13. The 11 Dec. 2006 atmospheric front Envisat ASAR WS image 11 December 2006, 14:03 UTC

  14. Sea surface wind field map of the waters surrounding Taiwan derived from Quikscat data acquired on 11 December 2006 at 10:49 UTC

  15. Zoom Weather radar image, 11 Dec. 2006, 14:00 UTC ZOOM: Envisat ASAR WS image, 11 December 2006,14:03 UTC

  16. Simulations carried out with the MM5 model Streamlines simulated with the MM5 model Wind field simulated with the MM5 model

  17. MODIS Terra image acquired on 12 December 2006 at 02:15 UTC

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  41. Examples of mesoscale atmospheric phenomena: • Coastal atmospheric fronts • Katabatic winds • Atmospheric gravity waves

  42. Occur late in the evening or at night • Require radiation weather, i.e., no clouds • Require calm weather Katabatic wind fields Envisat ASAR image acquired over the north eastern part of Taiwan on 29 July 2004 at 13:48 UTC or 21:48 local time.

  43. Katabatic wind No clouds Radiation weather Taiwan MODIS 29 July 2004, 0230 UTC

  44. Examples of mesoscale atmospheric phenomena: • Coastal atmospheric fronts • Katabatic winds • Atmospheric gravity waves

  45. Question: Are they sea surface signatures • of oceanic internal waves? On SAR images of the sea surface often wave patterns are visible. • or of atmospheric gravity waves?

  46. Oceanic internal waves in the South China Sea Dongsha Coral Reef ASAR WS, 21 June 2005, 14:09 UTC

  47. Atmospheric gravity wave ASAR IM, 26 May 2007, 13:48 UTC, Yellow Sea Institute of Oceanography University of Hamburg

  48. Atmospheric gravity waves Oceanic internal waves ASAR AP image, Yellow Sea, 2 Sept.2007, 13:37 UTC Swath width: 100 km

  49. 2) atmospheric internal waves Nonlinear atmospheric internal waves appear on SAR images usually as broad bright bands surrounded by narrow dark bands. σ= B /U + ΔU/ α SAR imaging of nonlinear waves 1) oceanic internal waves Nonlinear oceanic internal waves appear on SAR images usually as narrow very bright bands followed by narrow dark bands. Between them are broad bands of background image intensity. σ = σ0 ( 1 + A dux/dx) The wave pattern looks “crisp“. The wave pattern looks “soft“.

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