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Seasonal Evolution (seasonal + evolution)

Distribution by Scientific Domains

Earth and Environmental Science	75%

Selected Abstracts

Seasonal evolution of Titan's dark polar hood: midsummer disappearance observed by the Hubble Space Telescope

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
Ralph D. Lorenz
ABSTRACT Titan, Saturn's largest moon, has a dense organic-laden atmosphere that displays dramatic seasonal variations in composition and appearance. Here we document the evolution of the dark polar hood, first seen in 1980 by Voyager 1 around the north pole, and report quantitative measurements of the hood's disappearance from the south pole in 2002,2003 using previously unpublished observations with the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS). These data support a model of the hood as a transient structure associated with downwelling during polar winter. [source]

Spatio-temporal distribution of albacore (Thunnus alalunga) catches in the northeastern Atlantic: relationship with the thermal environment

FISHERIES OCEANOGRAPHY, Issue 2 2010
Y. SAGARMINAGA
Abstract When the spring seasonal warming starts, North Atlantic albacore (Thunnus alalunga) juveniles and pre-adults perform a trophic migration to the northeastern Atlantic, to the Bay of Biscay and to the southeast of Ireland. During this migration, they are exploited by Spanish trolling and baitboat fleets. The present study analyzes the relationship between the albacore spatio-temporal distribution and the thermal environment. For this approach, several analyses have been performed on a database including fishing logbooks and sea surface temperature (SST) images, covering the period between 1987 and 2003. SST values and the SST gradients at the catch locations have been statistically compared to broader surrounding areas to test whether the thermal environment determines the spatial distribution of albacore. General additive models (GAM) have been used also to evaluate the relative importance of environmental variables and fleet behaviour. The results obtained show that, although juvenile albacore catch locations are affected by fleet dynamics, there is a close spatial and temporal relationship with the seasonal evolution of a statistically significant preferential SST window (16,18°C). However, differences have been identified between the relationship of albacore with SST within the Bay of Biscay in July and August (higher temperature). Such differences are found also in the spatial distribution of the catch locations; these reflect clearly the presence of two groups, differentiated after the third week of the fishing campaign at the end of June. The analysis undertaken relating the distribution of North Atlantic albacore juveniles with thermal gradients did not provide any evidence of a relationship between these catch locations and the nearby occurrence of thermal gradients. [source]

Response of the summer atmospheric circulation over East Asia to SST variability in the tropical Pacific

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2010
Rena Nagata
Abstract General circulation over East Asia and its linkages with sea surface temperature (SST) variability over the tropical Pacific is investigated for the 1958,2000 period. The western edge of the North Pacific subtropical high (NPSH) index (SHI) is defined from pentad 31 (May 31 to June 4) to pentad 49 (August 29 to September 2). A southwestward extension of the SHI has been observed since 1980. The changes in the NPSH are associated with SST warming in the tropical eastern Pacific and Indian Ocean. On the basis of the SHI, years with western, eastern, southern and northern displacement of the NPSH are defined as WD, ED, SD and ND years. WD and SD years occur after 1980. Climatologically, the subsidence is located around 30°N in the western Pacific. This subsidence area corresponds to the NPSH region. Before pentad 40 in WD and SD years, associated with warm SST anomalies, circulation anomalies show an ascending motion over the tropical eastern Pacific and Indian Ocean. This ascending motion induces the anomalous subsidence over the tropical western Pacific and causes the southwestward extension of the NPSH. After pentad 40 (July 15,19), the seasonal evolution of WD years is different from the SD years. After pentad 40 in WD years, associated with large warm SST anomalies over the tropical eastern Pacific and Indian Ocean, the strong anomalous ascending motion strengthens the anomalous subsidence in the western tropical Pacific and leads to the lack of the eastward contraction of the NPSH. In SD years, warm SST anomalies over the tropical eastern Pacific and Indian Ocean weakened after pentad 40. Correspondently, the weakened anomalous ascending motion over these regions provides the weak anomalous subsidence over the tropical western Pacific. The weakened anomalous subsidence leads to the eastward contraction of the NPSH after pentad 40 similar to the climatological evolution. Copyright © 2009 Royal Meteorological Society [source]

Life cycle of the QBO-modulated 11-year solar cycle signals in the Northern Hemispheric winter

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 641 2009
Hua Lu
Abstract This paper provides some insights on the quasi-biennial oscillation (QBO) modulated 11-year solar cycle (11-yr SC) signals in Northern Hemisphere (NH) winter temperature and zonal wind. Daily ERA-40 Reanalysis and ECMWF Operational data for the period of 1958,2006 were used to examine the seasonal evolution of the QBO-solar cycle relationship at various pressure levels up to the stratopause. The results show that the solar signals in the NH winter extratropics are indeed QBO-phase dependent, moving poleward and downward as winter progresses with a faster descent rate under westerly QBO than under easterly QBO. In the stratosphere, the signals are highly significant in late January to early March and have a life span of ,30,50 days. Under westerly QBO, the stratospheric solar signals clearly lead and connect to those in the troposphere in late March and early April where they have a life span of ,10 days. As the structure changes considerably from the upper stratosphere to the lower troposphere, the exact month when the maximum solar signals occur depends largely on the altitude chosen. For the low-latitude stratosphere, our analysis supports a vertical double-peaked structure of positive signature of the 11-yr SC in temperature, and demonstrates that this structure is further modulated by the QBO. These solar signals have a longer life span (,3,4 months) in comparison to those in the extratropics. The solar signals in the lower stratosphere are stronger in early winter but weaker in late winter, while the reverse holds in the upper stratosphere. Copyright © 2009 Royal Meteorological Society [source]