Table 1 EDJ parameters

From: Intraseasonal shift in the wintertime North Atlantic jet structure projected by CMIP6 models

Mathematical expression

Description

\({{\rm {Lat}}}=\mathop{\max }\limits_{\phi \,\in \,[15^{\circ} {\rm{N}},75^{\circ} {\rm{N}}]}{U}_{{\rm {c}}}(\phi )\)

The latitude at which Uc attains its maximum.

\({\rm {{Int}}}={U}_{{\rm {c}}}({{\rm {Lat}}})\)

The Uc value at Lat.

\({{\rm {Sh}}}={{\rm {Int}}}-{\overline{U(\phi )}}_{{\rm {c}}}:\phi \in [15^{\circ} {\rm{N}},75^{\circ} {\rm{N}}]\)

The difference between Int and the meridional mean of Uc over all latitudes [15°N, 75°N].

\({{U}_{{\rm {c}}}\left({{\rm{Latn}}}\right)\atop{{{\rm {Latn}}}\in \left[{{\rm {Lat}}},75^{\circ} {\rm {N}}\right]}}={{\rm {Int}}}-{{\rm {Sh}}}/2\)

Latn: The latitude of the poleward flank of EDJ where Uc decreases the half of Sh.

\({{{U}_{{\rm {c}}}({{\rm {Lats}}})}\atop{{{\rm {Lats}}}\in [15^{\circ} N,{{\rm {Lat}}}]}}={{\rm {Int}}}-{{\rm {Sh}}}/2\)

As Latn but for the equatorward flank.

\(\begin{array}{l}{{\rm {Til}}}=60{\cdot b}\\{{{\rm {Lat}}}}_{\lambda }^{* }\, \sim {a}+{b\,\cdot\,}\lambda :{\rm{\lambda }}\in [60^{\circ} {\rm{W}},0^{\circ}]\end{array}\)

The slope of the tracked latitudes (Lat*λ) of Lat along the NATL.

\({{\rm {Lon}}}=\mathop{\sum }\limits_{\lambda =60^{\circ} {\rm{W}}}^{0^{\circ}}\lambda \cdot {{{{\rm {Int}}}}_{\lambda }}^{2}/\mathop{\sum }\limits_{\lambda =60^{\circ} {\rm{W}}}^{0^{\circ}}{{{{\rm {Int}}}}_{\lambda }}^{2}\)

The average of the NATL longitudes weighted by the square of Intλ (the zonal wind at Lat*λ).

\(\left[{{\rm {Lonw}}},{{\rm {Lone}}}\right]\in \left[90^{\circ} {\rm{W}},30^{\circ} {\rm{E}}\right]:\Delta {{{\rm {Int}}}}_{[{{\rm {Lonw}}},{{\rm {Lone}}}]}\ge 0.5\cdot \Delta {{{\rm {Int}}}}_{[60^{\circ} {\rm {W}},0^{\circ}]}\)

The longitudinal interval [Lonw, Lone] around Lon containing half of the Intλ contours over the NATL.

\({{\rm {Dep}}}=\sqrt{\frac{\mathop{\sum }\nolimits_{\lambda =60^{\circ} {\rm{W}}}^{0^{\circ}}{\left({{{\rm {Lat}}}}_{\lambda }-{{{\rm {Lat}}}}_{\lambda }^{* }\right)}^{2}}{n}}\)

The spread in the location of the latitudinal wind maxima (Latλ) obtained for the n longitudinal sectors of the NATL with respect to the fitted Lat*λ.

  1. Mathematical expressions synthesising the computation of the EDJ parameters (left column) and a brief explanation (right column). The zonal mean of u850 averaged over a longitudinal sector of 60° width is denoted by Uλ, with λ indicating the half longitude of the sector (the subindex c refers to the centre of the NATL sector, i.e. λ = 30°W). The latitudes are represented by \(\phi\). The intercept and slope of the linear regression are denoted by \(a\) and \(b.\,{{{\rm {Lat}}}}_{\lambda }^{* }\) depicts the latitudes obtained from the zonal tracking of the latitudinal peak \({{\rm {Lat}}}\) over the Uλ profiles of the NATL sector, so that contiguous values cannot differ by more than 5°. \({{{\rm {Lat}}}}_{\lambda }\) identifies the latitudes of the wind peak in Uλ, which do not necessarily coincide with \({{{\rm {Lat}}}}_{\lambda }^{* }\). See the “Methods” section for details.
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