COHERENT PATTERNS OF INTERANNUAL VARIABILITY OF THE ATMOSPHERIC CIRCULATION: THE ROLE OF INTRASEASONAL VARIABILITY

Abstract This study investigates the role of large-scale environmental factors, notably sea surface temperature (SST), low-level relative vorticity, and deep-tropospheric vertical wind shear, in the interannual variability of November–April tropical cyclone (TC) activity in the Australian region. Extensive correlation analyses were carried out between TC frequency and intensity and the aforementioned large-scale parameters, using TC data for 1970–2006 from the official Australian TC dataset. Large correlations were found between the seasonal number of TCs and SST in the Niño-3.4 and Niño-4 regions. These correlations were greatest (−0.73) during August–October, immediately preceding the Australian TC season. The correlations remain almost unchanged for the July–September period and therefore can be viewed as potential seasonal predictors of the forthcoming TC season. In contrast, only weak correlations (<+0.37) were found with the local SST in the region north of Australia where many TCs originate; these were reduced almost to zero when the ENSO component of the SST was removed by partial correlation analysis. The annual frequency of TCs was found to be strongly correlated with 850-hPa relative vorticity and vertical shear of the zonal wind over the main genesis areas of the Australian region. Furthermore, correlations between the Niño SST and these two atmospheric parameters exhibited a strong link between the Australian region and the Niño-3.4 SST. A principal component analysis of the SST dataset revealed two main modes of Pacific Ocean SST variability that match very closely with the basinwide patterns of correlations between SST and TC frequencies. Finally, it is shown that the correlations can be increased markedly (e.g., from −0.73 to −0.80 for the August–October period) by a weighted combination of SST time series from weakly correlated regions.

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Ice conditions interannual variability in the Antarctic Peninsula region and its connection with the atmospheric circulation indexes

Ukrainian Antarctic Journal ◽

10.33275/1727-7485.6-7.2008.508 ◽

2008 ◽

pp. 167-174

Author(s):

Ju. V. Artamonov ◽

◽

E. A. Skripaleva ◽

Ant. A. Bukatov ◽

◽

...

Keyword(s):

Interannual Variability ◽

Atmospheric Circulation ◽

Antarctic Peninsula ◽

Ice Conditions ◽

The Antarctic

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Recent changes of relative humidity: regional connection with land and ocean processes

10.5194/esd-2017-43 ◽

2017 ◽

Cited By ~ 3

Author(s):

Sergio M. Vicente-Serrano ◽

Raquel Nieto ◽

Luis Gimeno ◽

Cesar Azorin-Molina ◽

Anita Drumond ◽

...

Keyword(s):

Relative Humidity ◽

Interannual Variability ◽

Air Temperature ◽

Spatial Scales ◽

Global Scale ◽

Sea Surface ◽

Positive Trend ◽

Source Regions ◽

Strong Agreement

Abstract. We analyzed changes in surface relative humidity (RH) at the global scale from 1979 to 2014 using both observations and ERA-Interim dataset. We compared the variability and trends of RH with those of land evapotranspiration and ocean evaporation in moisture source areas across a range of selected regions worldwide. The sources of moisture for each particular region were identified by integrating different observational data and model outputs into a lagrangian approach. The aim was to account for the possible role of changes in air temperature over land, in comparison to sea surface temperature (SST), on RH variability. Results demonstrate a strong agreement between the interannual variability of RH and the interannual variability of precipitation and land evapotranspiration in regions with continentally-originated humidity. In contrast, albeit with the dominant positive trend of air temperature/SST ratio in the majority of the analyzed regions, the interannual variability of RH in the target regions did not show any significant correlation with this ratio over the source regions. Also, we did not find any significant association between the interannual variability of oceanic evaporation in the oceanic humidity source regions and RH in the target regions. Our findings stress the need for further investigation of the role of both dynamic and radiative factors in the evolution of RH over continental regions at different spatial scales.

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The role of air-sea coupling on the simulation of intraseasonal rainfall variability over the South Pacific in ECHAM5-SIT

10.5194/egusphere-egu21-12770 ◽

2021 ◽

Author(s):

Sunil Kumar Pariyar ◽

Noel Keenlyside ◽

Wan-Ling Tseng

Keyword(s):

General Circulation ◽

Rainfall Variability ◽

Intraseasonal Variability ◽

Phase Relationship ◽

Coupled Model ◽

South Pacific ◽

South Pacific Convergence Zone ◽

The South ◽

The Impact

We investigate the impact of air-sea coupling on the simulation of the intraseasonal variability of rainfall over the South Pacific using the ECHAM5 atmospheric general circulation model coupled with Snow-Ice-Thermocline (SIT) ocean model. We compare the fully coupled simulation with two uncoupled simulations forced with sea surface temperature (SST) climatology and daily SST from the coupled model. The intraseasonal rainfall variability over the South Pacific Convergence Zone (SPCZ) is reduced by 17% in the uncoupled model forced with SST climatology and increased by 8% in the uncoupled simulation forced with daily SST. The coupled model best simulates the key characteristics of the two intraseasonal rainfall modes of variability in the South Pacific, as identified by an Empirical Orthogonal Function (EOF) analysis. The spatial structure of the two EOF modes in all three simulations is very similar, suggesting these modes are independent of air-sea coupling and primarily generated by the dynamics of the atmosphere. The southeastward propagation of rainfall anomalies associated with two leading rainfall modes in the South Pacific depends upon the eastward propagating Madden-Julian Oscillation (MJO) signals over the Indian Ocean and western Pacific. Air-sea interaction seems crucial for such propagation as both eastward and southeastward propagations substantially reduced in the uncoupled model forced with SST climatology. Prescribing daily SST from the coupled model improves the simulation of both eastward and southeastward propagations in the uncoupled model forced with daily SST, showing the role of SST variability on the propagation of the intraseasonal variability, but the periodicity differs from the coupled model. The change in the periodicity is attributed to a weaker SST-rainfall relationship that shifts from SST leading rainfall to a nearly in-phase relationship in the uncoupled model forced with daily SST.

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