Atmospheric Internal Solitary Waves observed by MERIS/ASAR in the Mozambique Channel, Africa.

1. Atmospheric Internal Solitary Waves observed by MERIS/ASAR in the Mozambique Channel, Africa. Jorge Magalhães (jmagalhaes@fc.ul.pt), J. C. da Silva, Institute of Oceanography & Department of Physics, University of Lisbon Roger Grimshaw and Mathew Pearce. Department of Mathematical Sciences, Loughborough University, U.K.. September 29, 2005 ESA-ESRIN, Frascati, Italy.

2. Acknowledgements • ESA project AOPT-2423, A Multi-sensor Analysis and Interpretation System for the Coastal Zone Remote Sensing (AMAZING). • INTAS – SIMP (03-51-4987): Slicks as Indicators of Marine Processes. • Modis satellite data: http://daac.gsfc.nasa.gov • Atmospheric soundings: http://weather.uwyo.edu • Surface wind velocity data: www.ssmi.com

3. Motivations • Atmospheric internal solitary waves are recognized to be an important component of the dynamics of the atmospheric boundary layer. • They represent a fundamental element in the weather evolution for tropical Africa (Leroux, 2001). • In the Mozambique Channel this kind of phenomena is often associated with rain and thunderstorms (Leroux, 2001). • Why is this important for Remote Sensing? Discrimination between oceanic and atmospheric internal waves.

4. Aims: • Recently discovered area, with high occurrence frequency of internal waves, both atmospheric and oceanic. • Their main physical properties and propagation characteristics. • New physical parameter which seems to be a strong indicator of favorable propagating conditions for the atmospheric internal waves. • New possible method to detect and reveal the presence of atmospheric internal waves (synergy of MERIS /Scatterometer/ SAR).

5. Introduction Atmospheric internal solitary waves are very popular in the Gulf of Carpentaria (Australia). The so called...Morning Glories

6. Characterized by horizontal scales of a 100 meters to a few kilometers and phase speeds in the order of 10 ms-1. They usually appear as an amplitude-order series of waves of elevation. Atmospheric internal waves that propagate in the atmosphere fall broadly in to two classes: Those that propagate in a fairly shallow stratified layer above the earth’s surface. Those that occupy the entire troposphere. Introduction

7. MozambiqueChannel Why the Mozambique Channel? • Recently discovered area, very promising potential, never studied before… • Very rich in oceanic and atmospheric internal waves.

8. MozambiqueChannel • Statistical approach referring to 2nd semester of 2002. • Data collected from Meris, ASAR and Modis sensors. • Daily record of atmospheric internal waves presence in the Mozambique Channel. Column charts addressing the phenomenon's temporal and spatial variability.

9. MozambiqueChannel Similar conclusions for all three sensors: High frequency of atmospheric internal waves during the winter period (Southern Hemisphere).

10. Atmospheric internal waves in the MozambiqueChannel • High frequency of atmospheric internal waves in the Mozambique Channel. • Enables us to conduct a systematic and trustworthy survey capable of characterizing the phenomena's physical properties. • Supplies with the means necessary to compare the experimental outcomes with those predicted by theoretical models.

11. Atmospheric internal waves in the MozambiqueChannel How to describe atmospheric internal gravity waves from a physical point of view and indicate their more salient properties? Using a computer program, developed with IDL computer language, that analyses the available data, and calculates several physical parameters of particular interest such as the buoyancy frequency and the Scorer parameter.

12. Comparing data results with theoretical models • Absolute necessity for the existence of internal waves is a horizontal wave guide which inhibits the wave energy from propagating away in the vertical direction. How can we characterize the wave guide from a physical point of a view?

13. Comparing data results with theoretical models • What constitutes suitable boundary conditions? • Determine the depth of the waveguide. Analyze Scorer’s Parameter vertical profile.

14. Scorer Parameter Brunt-Väisälä frequency Wave’s phase speed Mean wind velocity component in the direction of the wave propagation

15. Scorer Parameter Scorer Parameter's behavior is govern by two intrinsically distinct factors: • N2: Measures the atmospheres stability. d2u0 : Indicator of shear effect. dz2

16. Meris High Resolution Image Mozambique Channel, 16 September 2004

17. Case study: 16 August 2002 Shear Effect (s-2) ScorerParameter (m-2) Buoyancy Frequency (s-1)

18. Subsidence Parameter • Represents a strong indicator of favorable propagating conditions for atmospheric internal waves. • Measures the strength of sudden and abrupt changes in dew point temperature vertical profile. Subsidence Area!! Total ΔZ Total ΔT ΔT/ΔZ in the Subsidence Area Subsidence Parameter = Total ΔT/Total ΔZ Typical dew point temperature vertical profile.

19. Subsidence Parameter Evolution of the Scorer parameter over time for the Antananarivo station August, 2002

20. High Resolution Image Mozambique Channel, 16 August 2002

21. Subsidence Parameter • Strong correlation between high values of the Subsidence Parameter and the presence of internal waves. • Represents a starting point in atmospheric internal wave’s favorable generating conditions forecast. • Atmospheric internal waves play important role in the weather evolution for tropical Africa. • Important from the meteorological point of a view.

22. A new insight: • Present what seems to be a new remote sensing method to detect and reveal internal solitary waves. • Is it possible for the solitary waves to produce a signature in the surface wind velocity field? • Present the wind velocity field in the Mozambique Channel at the surface level for 22nd of August 2004.

23. A new insight: Mozambique Channel, 22 August 2004

24. A new insight: Mozambique Channel, 22 August 2004

25. Meris High Resolution Image Mozambique Channel, 22 August 2004

26. A new insight: Mozambique Channel, 22 August 2004

27. Conclusions: • Mozambique Channel → High potential for internal wave’s study. • Importance of the Scorer Parameter to the definition of the waveguide’s properties. • Positive correlation between the presence of atmospheric internal waves and high values of the Subsidence Parameter. • Atmospheric solitary waves produce a measurable signature in the wind velocity field (Scatterometer /ASAR).