Retrieving characteristics of inertia gravity wave parameters with least uncertainties using the hodograph method

Abstract

Abstract. We have analyzed wind velocities measured with high-resolution Global Positioning System (GPS) radiosondes which have been flown continuously from Hyderabad for 120 h with an interval of 6 h. Hodograph method has been used to retrieve inertia gravity waves (IGWs) parameters. Background winds are removed from the time series by detrending, whereas polynomials of different orders are removed to obtain the fluctuations from individual profiles. A Butterworth filter is used to extract the monochromatic IGW component. Another filter finite impulse response (FIR1) is tried in a similar manner to test the effects of filters in estimating IGW characteristics. Results reveal that the fluctuation profiles differ with the change in polynomial orders, but the IGW parameters remain same when a Butterworth filter is chosen to extract the monochromatic wave component. The FIR1 filter produces results with a broader range. The direction of wave propagation can be confirmed with additional temperature information.

A Brief Overview of Gravity Wave Retrieval Techniques From Observations

“…The bispectral analysis is helpful to explain nonlinear resonant wave-wave interactions (Wüst and Bittner, 2006). The rotary spectral technique (Vincent, 1984) or Hodograph analysis (Hirota and Niki, 1985) is popular to characterize the inertia gravity wave intrinsic frequency and propagation direction, though it demands the presence of a single coherent wave source and does not yield good results at the mixture of different frequencies present in the perturbation profiles (Dutta et al, 2017). In general, in a plot of fluctuation components of winds, an ellipse would be fit and the rotational direction of the ellipse would decide the propagation direction of waves.…”

“…The difference between soundings and the background profiles defines the wave field which can be filtered out by using a Fourier transform to remove the very high or very low frequency oscillations. Dutta et al (2017) reported the use of different order polynomial fits (2-9) as the background on observed instantaneous wind profiles by global positioning system radiosondes over Hyderabad (17.4 °N, 78.5 °E). They observed the difference of wave parameters calculated by varying order of polynomials, and found reasonably reduced difference when a "Butterworth" filter was applied to extract inertia gravity wave components.…”

Gravity Wave Activities Associated With Convective Phenomena at a Tropical Location Near Land‐Sea Boundary

“…The hodograph analysis is obtained from the perturbation components of zonal ( u ′) and meridional wind ( v ′) of the ECMWF 91 model level data over Kolkata to estimate the energy propagation direction with a uncertainty of 180° (Vincent & Joan Alexander, ). To reduce the uncertainty the temperature perturbation has been plotted with the in‐phase velocity (Dutta et al, ). In‐phase wind is U cos ѳ, where U is the total wind and ѳ is the orientation angle of the u ′‐ v ′ hodograph.…”

“…In‐phase wind is U cos ѳ, where U is the total wind and ѳ is the orientation angle of the u ′‐ v ′ hodograph. The clockwise rotation of in‐phase wind and temperature perturbation hodograph indicates horizontal wave propagation along the orientation angle of u ′‐ v ′ hodograph (Dutta et al, ). Counterclockwise rotation indicates the propagation direction in the opposite direction (Dutta et al, ).…”

Gravity waves generated by thunderstorms

“…The model basically calculates the phase velocity and amplitude of the wave generated from a thunderstorm. The individual vertical profiles of radiosonde can be used to determine the perturbation in the horizontal wind profiles and also the power spectrum of the signal [76], [82]. The power spectrum is analysed for significant waves based on the red-noise spectrum, and the most dominant frequency is used for the conclusion here.…”