TY - JOUR

T1 - The power distribution between symmetric and antisymmetric components of the tropical wavenumber frequency spectrum

AU - Shamir, Ofer

AU - Schwartz, Chen

AU - Garfinkel, Chaim I.

AU - Paldor, Nathan

N1 - Publisher Copyright:
© 2021 American Meteorological Society.

PY - 2021/6

Y1 - 2021/6

N2 - A yet unexplained feature of the tropical wavenumber frequency spectrum is its parity distribution, i.e., the distribution of power between the meridionally symmetric and antisymmetric components of the spectrum. Due to the linearity of the decomposition to symmetric and antisymmetric components and the Fourier analysis, the total spectral power equals the sum of the power contained in each of these two components. However, the spectral power need not be evenly distributed between the two components. Satellite observations and reanalysis data provide ample evidence that the parity distribution of the tropical wavenumber frequency spectrum is biased toward its symmetric component. Using an intermediate-complexity model of an idealized moist atmosphere, we find that the parity distribution of the tropical spectrum is nearly insensitive to large-scale forcing, including topography, ocean heat fluxes, and land sea contrast. On the other hand, we find that a small-scale (stochastic) forcing has the capacity to affect the parity distribution at large spatial scales via an upscale (inverse) turbulent energy cascade. These results are qualitatively explained by considering the effects of triad interactions on the parity distribution. According to the proposed mechanism, any bias in the small-scale forcing, symmetric or antisymmetric, leads to symmetric bias in the large-scale spectrum regardless of the source of variability responsible for the onset of the asymmetry. As this process is also associated with the generation of large-scale features in the tropics by small-scale convection, the present study demonstrates that the physical process associated with deep convection leads to a symmetric bias in the tropical spectrum.

AB - A yet unexplained feature of the tropical wavenumber frequency spectrum is its parity distribution, i.e., the distribution of power between the meridionally symmetric and antisymmetric components of the spectrum. Due to the linearity of the decomposition to symmetric and antisymmetric components and the Fourier analysis, the total spectral power equals the sum of the power contained in each of these two components. However, the spectral power need not be evenly distributed between the two components. Satellite observations and reanalysis data provide ample evidence that the parity distribution of the tropical wavenumber frequency spectrum is biased toward its symmetric component. Using an intermediate-complexity model of an idealized moist atmosphere, we find that the parity distribution of the tropical spectrum is nearly insensitive to large-scale forcing, including topography, ocean heat fluxes, and land sea contrast. On the other hand, we find that a small-scale (stochastic) forcing has the capacity to affect the parity distribution at large spatial scales via an upscale (inverse) turbulent energy cascade. These results are qualitatively explained by considering the effects of triad interactions on the parity distribution. According to the proposed mechanism, any bias in the small-scale forcing, symmetric or antisymmetric, leads to symmetric bias in the large-scale spectrum regardless of the source of variability responsible for the onset of the asymmetry. As this process is also associated with the generation of large-scale features in the tropics by small-scale convection, the present study demonstrates that the physical process associated with deep convection leads to a symmetric bias in the tropical spectrum.

KW - Asymmetry

KW - Atmosphere

KW - Shallow-water equations

KW - Spectral analysis/models/distribution

KW - Tropics

UR - http://www.scopus.com/inward/record.url?scp=85108676914&partnerID=8YFLogxK

U2 - 10.1175/JAS-D-20-0283.1

DO - 10.1175/JAS-D-20-0283.1

M3 - ???researchoutput.researchoutputtypes.contributiontojournal.article???

AN - SCOPUS:85108676914

SN - 0022-4928

VL - 76

SP - 1983

EP - 1998

JO - Journal of the Atmospheric Sciences

JF - Journal of the Atmospheric Sciences

IS - 6

ER -