Remote weather associated with South Pacific subtropical sea‐level high properties

Abstract

The subtropical highs in sea-level pressure (SLP) are little studied and incompletely understood. In recent years, three groups of theories, i.e. tropical divergent circulations, subtropical Rossby wavetrains, and midlatitude frontal cyclone interactions, have been proposed for remote maintenance of these highs. The latter is presented here as a remote forcing of these highs for the first time in the reviewed literature. The focus of the study is upon illuminating associations between these mechanisms and the South Pacific subtropical high in SLP (SP high). Precipitation, outgoing longwave radiation, velocity potential, and divergent winds are used as proxy markers for the remote forcing mechanisms. The tools used include composites, one-point correlations, autocorrelations, cross-correlations, and cross-spectra. Observational evidence, in monthly and daily data, is examined that appears to support each mechanism. Associations seen in monthly data are better understood in daily data at various lags. Convection over Amazonia, coordinated with suppressed convection in the western tropical Pacific, leads to enhanced SLP on the tropical side of the high. Midlatitude weather systems are the strongest influence upon the maximum SLP and the SLP on the higher latitude side of the high. The western side is associated with both middle-and lower-latitude phenomena, such as the South Pacific convergence zone. Various properties of the high have a strong period around 45 days. Associations to the Madden-Julian oscillation and El Niño-southern oscillation are explored and are strong only for the tropical side of the SP high.

Remote weather associated with North Pacific subtropical sea level high properties

“…From these, divergent wind components and velocity potential (VP) were calculated. In Grotjahn (2004), VP was a more reliable field than daily P for the SP high. For the NP high, VP was not as useful an indicator of divergent circulations associated with midlatitude frontal cyclones than were divergent wind components.…”

“…This Southern Hemisphere association suggests a common link rather than a direct connection. Evidence for a common link is found in Grotjahn (2004): a stronger South Pacific subtropical high (SP high) is associated with (a) South Pacific storm track shifted south, and (b) greater Indonesian-region P, though the stronger SP high preceded the stronger Indonesian P in lag/lead correlations of daily anomaly data. The proposed link to surface temperature is not addressed by these monthly mean correlations.…”

“…The data and data analysis tools are similar to Grotjahn (2004). Therefore, only brief descriptions of the data and analysis methods are listed here.…”

“…The first paper, Grotjahn (2004), focused upon associating variations of remote events with variations of the South Pacific subtropical high (hereafter SP high). This paper is an analogous study of the subtropical high of the North Pacific (hereafter NP high).…”

“…Convergence of these upper level ageostrophic winds produces sinking above and on the eastern side of the subtropical highs. As mentioned, Grotjahn (2004) introduced consideration of extratropical cyclone/anticyclone forcing. One sees that connection by recognizing that those upper level equatorward ageostrophic winds arise from maintaining thermal wind balance for developing frontal cyclones.…”