author | Andreas Thurnherr <ant@ldeo.columbia.edu> |
Tue, 05 Mar 2019 10:03:40 -0500 | |
changeset 38 | 15c603bc4f70 |
parent 15 | libGM.pl@ebd8a4ddd7f2 |
child 39 | 56bdfe65a697 |
permissions | -rw-r--r-- |
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#====================================================================== |
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# L I B G M 7 6 . P L |
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# doc: Sun Feb 20 14:43:47 2011 |
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# dlm: Sat Feb 2 02:33:11 2019 |
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# (c) 2011 A.M. Thurnherr |
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# uE-Info: 144 43 NIL 0 0 70 2 2 4 NIL ofnI |
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#====================================================================== |
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# HISTORY: |
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# Feb 20, 2011: - created |
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# Feb 28, 2011: - cosmetics |
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# Mar 28, 2012: - BUG: N had been ignored (but only affects vertical |
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# wavelengths > 1000m in any was significantly |
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# - changed from Munk eqn 9.23b to 9.23a, which also |
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# affects only long wavelengths |
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# - return nan for omega outside internal-wave band |
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# Mar 29, 2012: - re-wrote using definition of B(omega) from Munk (1981) |
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# Aug 23, 2012: - cosmetics? |
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# Sep 7, 2012: - made N0, E0, b, jstar global |
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# Dec 28, 2012: - added allowance for small roundoff error to Sw() |
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parents:
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# Oct 6, 2014: - made omega optional in Sw() |
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# Nov 18, 2014: - made b & jstar mandatory for Sw() |
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# Feb 2, 2019: - renamed from libGM.pl to libGM76.pl |
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# - replaced beta with m |
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# - replaced old code based on Gregg + Kunze formalism with |
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# expressions from Thurnherr et al. (GRL 2015) |
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# - added GM_strain |
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# - BUG: Sw usage message had wrong parameter order |
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# - renamed Sw => GM_VKE; Su_z => GM_shear |
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require "$ANTS/libEOS83.pl"; |
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my($pi) = 3.14159265358979; |
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#====================================================================== |
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# Global Constants |
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#====================================================================== |
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$GM_N0 = 5.24e-3; # rad/s # reference stratification (from Gregg + Kunze, 1991) |
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$GM_E0 = 6.3e-5; # dimensionless # spectral level (Munk 1981) |
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$GM_b = 1300; # m # pycnocline e-folding scale |
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$GM_jstar = 3; # dimless # peak mode number |
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#====================================================================== |
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# Vertical velocity spectral density |
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# |
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# Units: K.E. per frequency per wavenumber [m^2/s^2*1/s*1/m = m^3/s] |
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# Version: GM76 |
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# |
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# E. Kunze (email, Feb 2011): The GM vertical velocity w spectrum is described by |
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# |
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# S[w](omega, k_z) = PI*E_0*b*{f*sqrt(omega^2-f^2)/omega}*{j*/(k_z + k_z*)^2} |
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# |
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# where E_0 = 6.3 x 10^-5 is the dimensionless spectral level, b = 1300 m is |
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# the pycnocline lengthscale, j* = 3 the peak mode number and k_z* the |
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# corresponding vertical wavenumber. The flat log-log spectrum implies w is |
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# dominated by near-N frequencies (where we know very little though Yves |
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# Desaubies wrote some papers back in the late 70's/early 80's about the |
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# near-N peak) and low modes. The rms w = 0.6 cm/s, right near your noise |
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# level. Interestingly, the only N dependence is in m and m*. As far |
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# as I know, little is known about its intermittency compared to horizontal |
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# velocity. Since w WKB-scales inversely with N, the largest signals should |
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# be in the abyss where you therefore likely have the best chance of |
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# measuring it. |
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# |
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# E. Kunze (email, Sep 19, 2013): |
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# |
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# S[w](omega, m) = PI*E0*b*[f*sqrt(omega^2-f^2)/omega]*[jstar/(m+mstar)^2] with |
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# |
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# S[w](m) = PI*E0*b*N*f*[jstar/(m+mstar)^2] |
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# |
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# where the nondimensional spectral energy level E0 = 6.3e-5, stratification |
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# lengthscale b = 1500 m, jstar = 3, mstar = jstar*PI*N/b/N0, and N0 = |
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# 5.3e-3 rad/s. |
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# |
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# NOTES: |
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# - b=1500m is a likely typo, as Gregg & Kunze (1991) have b=1300m |
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# - k_z == m |
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# |
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#====================================================================== |
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sub m($$) # vertical wavenumber as a function of mode number & stratification params |
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{ |
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my($j,$N,$omega) = @_; |
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return defined($omega) && ($omega <= $GM_N0) |
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? $pi / $GM_b * sqrt(($N**2 - $omega**2) / ($GM_N0**2 - $omega**2)) * $j |
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: $pi * $j * $N / ($GM_b * $GM_N0); # valid, except in vicinity of buoyancy turning frequency (Munk 1981, p.285) |
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} |
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sub B($) # structure function (omega dependence) |
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{ # NB: f must be defined |
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my($omega) = @_; |
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croak("coriolis parameter not defined\n") |
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unless defined($f); |
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return 2 / $pi * $f / $omega / sqrt($omega**2 - $f**2); |
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} |
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sub GM_VKE(@) |
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{ |
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my($omega,$m,$lat,$b,$jstar,$N) = |
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&antsFunUsage(-5,'fff','[frequency[1/s]] <vertical wavenumber[rad/m]> <lat[deg]> <b[m]> <j*> <N[rad/s]>',@_); |
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if (defined($N)) { # Sw(omega,m) |
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local($f) = abs(&f($lat)); |
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$omega += $PRACTICALLY_ZERO if ($omega < $f); |
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$omega -= $PRACTICALLY_ZERO if ($omega > $N); |
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return nan if ($omega < $f || $omega > $N); |
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my($mstar) = &m($jstar,$N,$omega); |
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return $GM_E0 * $b * 2 * $f**2/$omega**2/B($omega) * $jstar / ($m+$mstar)**2; |
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} else { # Sw(m), i.e. integrated over all omega; as in Thurnherr et al., GRL 2015 |
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$N = $lat; # shift arguments to account for missing omega |
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$lat = $m; |
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local($f) = abs(&f($lat)); |
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$m = $omega; |
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undef($omega); |
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my($mstar) = &m($jstar,$N); |
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return $pi * $GM_E0 * $b * $N * $f * $jstar / ($m+$mstar)**2; |
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} |
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} |
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#---------------------------------------------------------------------- |
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# Shear and Strain m-spectra (i.e. integrated over f) |
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# - spectral density |
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# - from Thurnherr et al. (GRL 2015) |
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#---------------------------------------------------------------------- |
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sub GM_shear(@) |
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{ |
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my($m,$lat,$b,$jstar,$N) = |
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&antsFunUsage(5,'fffff','<vertical wavenumber[rad/m]> <lat[deg]> <b[m]> <j*> <N[rad/s]>',@_); |
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local($f) = abs(&f($lat)); |
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my($mstar) = &m($jstar,$N); |
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return 3 * $pi/2 * $GM_E0 * $b * $jstar * $m**2 / ($m+$mstar)**2; |
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} |
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sub GM_strain(@) |
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{ |
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my($m,$lat,$b,$jstar,$N) = |
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&antsFunUsage(5,'fffff','<vertical wavenumber[rad/m]> <lat[deg]> <b[m]> <j*> <N[rad/s]>',@_); |
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local($f) = abs(&f($lat)); |
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my($mstar) = &m($jstar,$N); |
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return $pi/2 * $GM_E0 * $b * $jstar * $m**2 / ($m+$mstar)**2; |
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} |
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##---------------------------------------------------------------------- |
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## GM76, as per Gregg and Kunze (JGR 1991) |
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## - beta is vertical wavenumber |
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##---------------------------------------------------------------------- |
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# |
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#sub Su($$) |
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#{ |
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# my($beta,$N) = @_; |
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# |
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# my($beta_star) = &m($GM_jstar,$N); # A3 |
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# return 3*$GM_E0*$GM_b**3*$GM_N0**2 / (2*$GM_jstar*$pi) / (1+$beta/$beta_star)**2; # A2 |
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#} |
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# |
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#sub Su_z($$) |
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#{ |
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# my($beta,$N) = &antsFunUsage(2,'ff','<vertical wavenumber[rad/m]> <N[rad/s]>',@_); |
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# return $beta**2 * &Su($beta,$N); |
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#} |
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1; |