Fluctuations of radio occultation signals in sounding the Earth's atmosphere

Transcription

1 Fluctuations of radio occultation signals in sounding the Earth's atmosphere Valery Kan, Michael E. Gorbunov A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences Viktoria F. Sofieva Finnish Meteorological Institute

2 Contents Radio occultation sounding as a statistical problem Isotropic and anisotropic inhomogeneities: turbulence and IGW; their identification from occultation observations Basic models Results

3 Radio Occultations GPS signals: L1: HGz, cm L2: HGz, cm 1. The sounding of the Earth s atmosphere by means of GPS signals. 2. Retrieval of refractivity profiles. 3. Statistical study of internal gravity waves and turbulence.

4 Isotropic and Anisotropic Inhomogeneities Gurvich, A. S. and Brekhovskikh, V. L.: Study of the Turbulence and Inner Waves in the Stratosphere Based on the Observations of Stellar Scintillations from Space: A Model of Scintillation Spectra, Waves in Random Media, 11, , 2001.

5 Vertical vs Oblique Observation Geometry Gurvich, A. S. and Brekhovskikh, V. L.: Study of the Turbulence and Inner Waves in the Stratosphere Based on the Observations of Stellar Scintillations from Space: A Model of Scintillation Spectra, Waves in Random Media, 11, , 2001.

6 Scintillation Spectra Gurvich, A. S. and Kan, V.: Structure of air density irregularities in the stratosphere from spacecraft observations of stellar scintillation: 1.Three-dimensional spectrum model and recovery of its parameters, Izv. Atmos. Ocean. Phys., 39, , 2003.

7 N = n-1 n= N-N N ( ) / N r r ( ) ( ) ( ) F k =F k +F k 3D Models of Refractivity Fluctuation Spectra Refractive index Relative fluctuations of refractive index Locally spherically symmetric model of regular atmosphere n W K Fluctuation spectrum: W anisotropic component (Internal Gravity Waves, IGW), K isotropic Kolmogorov turbulence 2 2( ) -µ WK, /2 æ k ö F=F WK, = ACWK, h k z+hwk, k ^ + KWK, fç, ç èkwk, ø ( ) z W, K ^, ^ x y, exp / W, K k =k +h k k =k +k f= -k k 2 C WK, Structure constants WK, 1 µ WK, Spectrum power h ³ Anisotropy coefficients K k WK, WK, Outer scale wavenumber Inner scale wave number

8 3D Models of Refractivity Fluctuation Spectra µ= 5, h? 1, A = 1 Saturated IGWs µ= 11/ 3, h= 1, A = K n / C = C N Isotropic Kolmogorov turbulence

9 Phase Screen Approximation The eikonal fluctuation spectrum in the phase screen plane RH d F% æ ö k j k, k =Y F k, k + k exp - k R e H 0 ( ) ( ) 2 ò 2 2 e 0 2 x z y z x y ç 2 2 x è + k z H0 ø 1+ k z H0 - the Earth's radius - the atmospheric scale height Y= p RH N 2 e 0 Mean eikonal Gurvich, A. S.: Fluctuations During Observations of Extraterrestrial Sources from Space Through the Atmosphere of the Earth, Radiophysics and Quantum Electronics, 27, 665, 1984.

10 Amplitude and Phase Fluctuation Spectra 2D fluctuation spectra 2 k ì éxq ù Fc,, 1 cos q F%, 2 ê kg ú î ë û ( ) 1 ( k k = í m k + k ) ( ) j k k S z y z y z y q refractive attenuation γ relative distance from receiver to phase screen ü ý þ 1D fluctuation spectra as function of vertical wave number ( ) ( ) c V k = ò F k k dk c, S z, S z, y y 1D fluctuation spectra as function of oblique wave number ( ) ( ) Vc, S k s = ò Fc, S kssin a+k cos a, kscos a-k sin a dk

11 IGW, Turbulence, and Stellar Occultations 1. Smith, S. A., Fritts, D. C., and VanZandt, T. E.: Evidence of saturation spectrum of atmospheric gravity waves, J. Atmos. Sci., 44, , Tsuda, T., VanZandt, T. E.,Mizumoto,M., Kato, S., and Fukao, S.: Spectral analysis of temperature and Brunt-Vaisala frequency fluctuations observed by radiosondes, J. Geophys. Res., 96, , Nastrom, G. D., Gage, K. S., and Ecklund,W. L.: Variability of Turbulence, 4 20 km, in Colorado and Alaska from MST Radar Observations, J. Geophys. Res., 91, , Gracheva, M. E. and Gurvich, A. S.: A simple model for calculation of turbulence disturbances in optical devices, Izv. Akad. Nauk SSSR, Fiz. Atmos. Okeana, 16, , in Russian, Gurvich, A. S. and Kan, V.: Structure of air density irregularities in the stratosphere from spacecraft observations of stellar scintillation: 2. Characteristic scales, structure characteristics, and kinetic energy dissipation, Izv. Atmos. Ocean. Phys., 39, , 2003b. 6. Sofieva, V. F., Gurvich, A. S., Dalaudier, F., and Kan, V.: Reconstruction of internal gravity wave and turbulence parameters in the stratosphere using GOMOS scintillation measurements, J. Geophys. Res., 112, D12 113, doi: /2006jd007483, 2007a.

12 Stellar Occultation Spectra Figure 3. Illustration of the retrieval in two steps. Red thin line: the experimental (measured) spectrum. Black bold dashed line: the fit using all points of the measured spectrum, the first step fit (the values of retrieved parameters are given in the black box). Blue bold solid line: the fit after removal of two outliers (the points used in the retrieval are marked by black circles), the second step fit (the values of retrieved parameters are given in the blue box). Sofieva, V. F., Gurvich, A. S., Dalaudier, F., and Kan, V.: Reconstruction of internal gravity wave and turbulence parameters in the stratosphere using GOMOS scintillation measurements, J. Geophys. Res., 112, D12 113, doi: /2006jd007483, 2007a

13 Amplitude and Phase Fluctuation Spectra RMS fluctuation for model estimates of amplitude and phase fluctuations for isotropic (Kolomogorov turbulence) and anisotropic (saturated IGWs) inhomogeneities.

14 Amplitude Spectra Amplitude fluctuation spectra for the lower stratosphere: panel A: the isotropy hypothesis (Kolmogorov turbulence); panel B: the anisotropy hypothesis (saturated IGWs). The color map red green blue corresponds to the increasing obliquity angles, which are subdivided into three groups. The black solid line in panel B presents the theoretical vertical spectrum for the saturated IGW model; the dashed lines present the asymptotics of this spectrum for low and high frequencies. For the comparison, red dashed lines show the high-frequency spectral asymptotic of the Kolmogorov turbulence model.

15 Amplitude Spectra Amplitude fluctuation spectra for the upper troposphere: panel A: the isotropy hypothesis (Kolmogorov turbulence); panel B: the anisotropy hypothesis (saturated IGWs). The notations are the same as in previous Figure.

16 Eikonal Spectra The normalized eikonal fluctuation spectra for the lower stratosphere: panel A: the isotropy hypothesis; panel B: the anisotropy hypothesis. The black solid line in panel B represents the theoretical vertical spectrum for the saturated IGWmodel; the dashed line represents its asymptotics. For the comparison, red dashed lines show the high-frequency spectral asymptotic of the Kolmogorov turbulence model.

17 Eikonal Spectra The normalized eikonal fluctuation spectra for the upper troposphere. Panel A: the isotropy hypothesis; panel B: the anisotropy hypothesis. The notations are the same as in previous Figure.

18 Conclusion 1. We studied amplitude and phase variances of RO signal for typical parameters of 3D spectra based on two models: 1) the Kolmogorov turbulence and 2) saturated IGWs. 2. For GPS/MET observations in the altitude range of 4 25 km for middle and polar latitudes, we derived the amplitude and phase fluctuation spectra. 3. Both theoretical and experimental results indicate a dominant role of saturated IGWs in forming the fluctuations of RO signal at altitudes above 4 5 km in middle and polar latitudes, and above 7 8 km in the tropics. 4. Relationships that link IGW parameters and RO signal fluctuations may serve as a basis for the global monitoring of IGW parameters and activity from RO observations in the stratosphere and upper troposphere.

19 Acknowledgements The work of V. Kan and M. E. Gorbunov was supported by Russian Foundation for Basic Research, grant

20 Thanks for attention!