Intraseasonal variability of sea‐ice concentration in the Antarctic with particular emphasis on wind effect

Abstract

[1] This study investigated mechanisms for the intraseasonal variability of sea-ice concentration in the Antarctic, using Complex Empirical Orthogonal Function (CEOF) analysis of daily sea-ice concentration data during the period 1992 through 2001 derived from images of the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I). The first CEOF mode clearly showed that the large amplitudes of sea-ice concentration occur in the marginal sea-ice zone of the western Antarctic. The first mode also revealed the existence of eastward propagating phases with a period of 10-20 days in the western Antarctic. Regression analysis of meridional wind velocity onto the temporal coefficient of the first CEOF mode showed that the spatial phase of the meridional wind velocity precedes that of sea-ice concentration by about 90 degrees, indicating that the maximum change of sea-ice concentration occurs at the maximum wind velocity. From data analyses of ice-drifting velocity and simple sea-ice model results, it is suggested that thermodynamical effects such as sea-ice production are likely to contribute dominantly to the intraseasonal variability of sea-ice concentration in the marginal sea-ice zone of the western Antarctic.

The intraseasonal variability of winter semester surface air temperature in Antarctica

“…Those anomalies consistently propagate eastward correspondingly with the evolution of the modes. The wind vector anomaly also influences the sea-ice anomaly (Baba et al 2006;Lima & Carvalho 2008). In most cases the effect is confined to the Southern Ocean and Antarctic marginal sea regions.…”

“…Matthews & Meredith (2004) found that the variability of oceanic Antarctic circumpolar transport and the atmospheric SAM on intraseasonal (30 Á 70-day) timescales was related to the tropical atmospheric MJO during the southern winter. By means of complex empirical orthogonal functions (CEOFs), Baba et al (2006) reported that the largest amplitudes in variability along the marginal sea-ice zone occurred around West Antarctica, especially in the Amundsen and Bellingshausen seas, and that the spatial phase of the meridional wind velocity preceded that of sea-ice concentration by about 908. Lima & Carvalho (2008) demonstrated the relationship between mid-latitude atmospheric wave train and sea-ice area in the Amundsen and Bellingshausen seas and showed that the extreme sea-ice area anomalies on intraseasonal timescales (20 Á 100 days) lag behind the propagation of subtropical wave train in the Southern Hemisphere by approximately 10 Á 15 days.…”

“…Some researchers also studied intraseasonal oscillations in Southern mid-latitudes (Ghil & Mo 1991;Lau et al 1994;Mo & Higgins 1998). Although some studies have examined intraseasonal oscillations using a single station's meteorological data from Antarctica or sea-ice data in the Southern Ocean (Yasunari & Kodama 1993;Baba et al 2006), to our knowledge there have been no systematic studies of intraseasonal variability over the entire region south of 608 S. Given the critical role that Antarctica plays in global climate change, it is important to understand the causes of the intraseasonal oscillations in this region and their impact on Antarctic weather and climate. This paper presents a systematic analysis of the intraseasonal variability of surface air temperature in the region south of 608S and the possible reasons for the oscillation.…”

Anti-persistence in the global temperature anomaly field

“…The Madden-Julian oscillation (Madden and Julian, 1994) is one of the most powerful tropical phenomenon on intraseasonal time-scales that modulates cloudiness, precipitation and circulation over the tropics, with impacts on the subtropics and extratropics of both hemispheres (e.g, Lau and Waliser, 2005, and references therein). In addition, important variations on intraseasonal time-scales have been observed in temperature (Przybylak, 2002) and sea ice (Baba et al, 2006) records in high latitudes. However, the physical reasons for distinct scaling characteristics and, therefore, H over the continents and oceans are not obvious but suggest different responses of temperature fluctuations on intraseasonal time-scales.…”

“…However, uncertainties about the details of the natural variability as well as the response of the climate system to the rapid increase of greenhouse gases still remain (IPCC, 2007). Understanding natural variability of the climate system is crucial to predict non-linear climate forcings and abrupt changes possibly due to anthropogenic activity (Alley et al, 2003). The objective of this study is to imCorrespondence to: L. M. V. Carvalho (leila@model.iag.usp.br) prove our understanding of climate variability by providing new insights about the spatiotemporal variability of temperature anomalies.…”