Evidence for Equatorial Kelvin Modes in Nimbus-7 LIMS

Abstract

Eastward propagating disturbances over the equator are diagnosed in two independent Nimbus-7 LIMS (Limb Infrared Monitor of the Stratosphere) data sets. They are evident consistently at several pressure levels throughout the stratosphere and account for much of the temperature variance in the tropics. The disturbances, which can be seen in wavenumbers 1–3, are in phase and symmetric about the equator, latitudinally evanescent, and have short-moderate vertical phase structure, 10–40 km, which progresses downward. Wavenumber 1 has spectral components which propagate eastward at periods of 6.7–8.6 days (54–69 m s−1) and 3.5–4.0 days (115–135 m s−1). Wavenumber 2 exhibits eastward propagating variance at periods of 6.0–7.5 days (31–39 m s−1) and 3.8–4.3 days (55–62 m s−1). The faster waves appear principally in the upper stratosphere. These features are in reasonable agreement with the structure and dispersion characteristics of simple, quasi-separable Kelvin modes. With the exception of the slower w... Abstract Eastward propagating disturbances over the equator are diagnosed in two independent Nimbus-7 LIMS (Limb Infrared Monitor of the Stratosphere) data sets. They are evident consistently at several pressure levels throughout the stratosphere and account for much of the temperature variance in the tropics. The disturbances, which can be seen in wavenumbers 1–3, are in phase and symmetric about the equator, latitudinally evanescent, and have short-moderate vertical phase structure, 10–40 km, which progresses downward. Wavenumber 1 has spectral components which propagate eastward at periods of 6.7–8.6 days (54–69 m s−1) and 3.5–4.0 days (115–135 m s−1). Wavenumber 2 exhibits eastward propagating variance at periods of 6.0–7.5 days (31–39 m s−1) and 3.8–4.3 days (55–62 m s−1). The faster waves appear principally in the upper stratosphere. These features are in reasonable agreement with the structure and dispersion characteristics of simple, quasi-separable Kelvin modes. With the exception of the slower w...