Boreal Spring (boreal + spring)

Distribution by Scientific Domains

Selected Abstracts

At-sea distributions and abundance of tropicbirds in the eastern Pacific

IBIS, Issue 2 2005
During spring and autumn 1980,95, we surveyed Red-tailed Phaethon rubricauda, White-tailed P. lepturus and Red-billed Tropicbirds P. aethereus at sea in the Pacific between the coast of the Americas and 176°W. For the Pacific, we had complete coverage of the range of aethereus, but only partial coverage of that of rubricauda and lepturus. Six areas of higher density were indicated: three of rubricauda, two of lepturus and one of aethereus. After pooling data across years, the ,abundance' (total number including subadults and adults) estimate for rubricauda was 81 700 (boreal spring) and 86 500 (boreal autumn) birds. Abundance of each of the three rubricauda subpopulations differed between seasons by about 50% despite seasonal consistency when populations were grouped. Furthermore, high densities of rubricauda occurred at the edge of our study area, indicating that neither of the seasonal estimates for this species could be considered as total numbers. Abundance estimates of lepturus during the non-breeding season (when these birds had dispersed from colonies) were 11 000 and 41 500 birds for northern and southern populations, respectively. Estimated abundance of aethereus during the boreal spring was 26 700 birds, and 33 400 during the boreal autumn. Because tropicbirds are attracted to survey vessels, we also estimated the abundance after excluding those recorded as flying in a steady direction, or having been attracted to the ship. Considering only stationary birds (i.e. those that could not have been attracted), our minimum estimates were 41 000 rubricauda, 15 750 aethereus, 28 000 southern lepturus and 6400 northern lepturus. [source]

Interannual variability of boreal summer rainfall in the equatorial Atlantic

Guojun Gu
Abstract Tropical Atlantic rainfall variations during boreal summer (June,July,August (JJA)) are quantified by means of a 28-year (1979,2006) monthly precipitation dataset from the Global Precipitation Climatology Project (GPCP). Rainfall variability during boreal spring (March,April,May (MAM)) is also examined for comparison in that the most intense interannual variability is usually observed during this season. Comparable variabilities in the Atlantic maritime intertropical convergence zone (ITCZ) (15° ,35°W) strength (PITCZ) are found during both seasons. Variations in the ITCZ's latitudinal location (LatITCZ) during JJA, however, are much weaker than during MAM. PITCZ and LatITCZ are shown to be closely associated with sea surface temperature (SST) anomalies in both the tropical Atlantic and Pacific. Within the tropical Atlantic, the Atlantic Niño events (Atl3) and SST anomalies in the tropical North Atlantic (TNA) are the two major local factors modulating surface rainfall patterns and variations. Atl3 is significantly correlated with PITCZ and LatITCZ during JJA and MAM. TNA is significantly correlated to PITCZ during JJA but not to LatITCZ. In contrast, TNA is significantly correlated to LatITCZ during MAM but its correlation with PITCZ is weak. The impact of the El Niño-Southern Oscillation (ENSO) events (Nino3.4) is observed during both seasons, while the correlation between Nino3.4 and LatITCZ is slightly weak. However, with the effects of Atl3 and TNA removed, the ENSO tends to have a quite limited direct impact on the tropical Atlantic, specifically over the open ocean. High second-order partial correlation between Nino3.4 and rainfall is generally confined to the western basin and over the northeastern South America. Therefore, during JJA, the two local SST modes are of dominance for the tropical Atlantic rainfall variability. Nevertheless, the ENSO seems to still play an active role in modulating surface zonal wind anomalies in the western basin and then the Atlantic Niño mode. Copyright © 2008 Royal Meteorological Society [source]

Trend and variability of China precipitation in spring and summer: linkage to sea-surface temperatures

Fanglin Yang
Abstract Observational records in the past 50 years show an upward trend of boreal-summer precipitation over central eastern China and a downward trend over northern China. During boreal spring, the trend is upward over southeastern China and downward over central eastern China. This study explores the forcing mechanism of these trends in association with the global sea-surface temperature (SST) variations on the interannual and interdecadal time scales. Results based on singular value decomposition (SVD) analyses show that the interannual variability of China precipitation in boreal spring and summer can be well defined by two centres of action for each season, which are covarying with two interannual modes of SSTs. The first SVD modes of precipitation in spring and summer, which are centred in southeastern China and northern China respectively, are linked to an El Niño,southern oscillation (ENSO)-like mode of SSTs. The second SVD modes of precipitation in both seasons are confined to central eastern China, and are primarily linked to SST variations over the warm pool and the Indian Ocean. Features of the anomalous 850 hPa winds and 700 hPa geopotential height corresponding to these modes support a physical mechanism that explains the causal links between the modal variations of precipitation and SSTs. On the decadal and longer time scale, similar causal links are found between the same modes of precipitation and SSTs, except for the case of springtime precipitation over central eastern China. For this case, while the interannual mode of precipitation is positively correlated with the interannual variations of SSTs over the warm pool and Indian Ocean, the interdecadal mode is negatively correlated with a different SST mode, i.e. the North Pacific mode. The latter is responsible for the observed downward trend of springtime precipitation over central eastern China. For all other cases, both the interannual and interdecadal variations of precipitation can be explained by the same mode of SSTs. The upward trend of springtime precipitation over southeastern China and downward trend of summertime precipitation over northern China are attributable to the warming trend of the ENSO-like mode. The recent frequent summertime floods over central eastern China are linked to the warming trend of SSTs over the warm pool and Indian Ocean. Copyright © 2004 Royal Meteorological Society [source]

Intraseasonal variability of the ocean , atmosphere coupling in the Gulf of Guinea during boreal spring and summer

Gaëlle de Coëtlogon
Abstract Statistical analyses of the satellite TMI sea-surface temperature (SST) and QuikSCAT surface winds in boreal spring and summer are performed to investigate the intraseasonal variability of air,sea interactions in the Gulf of Guinea. There, empirical orthogonal function decomposition shows the existence of peaks around 15 days, and their lagged cross-correlation the signature of an expected 5-day lag wind forcing and 3-day lag strong negative SST feedback. Lagged linear regressions are performed onto a reference SST index of the cold tongue northern front in the Gulf of Guinea. A cold SST anomaly covering the equatorial and coastal upwelling is forced after about one week by stronger-than-usual south-easterlies linked to the St Helena anticyclone, suggesting that intraseasonal variability in the Gulf of Guinea is connected to large-scale fluctuations in the South Atlantic. Within about 5°S and 5°N, two retroactions between SST and surface wind appear to dominate near-surface atmosphere conditions. When the wind leads the SST, stronger monsoonal winds north of 2°N are partly sustained by the developing SST anomaly and bring more humidity and rainfall toward the continent. When the SST leads the wind, a reversal of anomalous winds is observed mainly south of 2°N, closing a negative feedback loop with a biweekly periodicity. Eventually, further investigation with an ocean model emphasizes the contribution of the horizontal advection in shaping these intraseasonal SST signals. The contribution of vertical processes may also be important but was more difficult to estimate. Copyright © 2010 Royal Meteorological Society [source]

Crunoecia irrorata (Curtis) (Trichoptera: Lepidostomatidae) and conservation of boreal springs: indications of clustering of red-listed species

Jari Ilmonen
Abstract 1.Crunoecia irrorata is widely dispersed across Europe, but rare and red-listed in Finland. Its geographical range comprises most of the southern boreal zone in Fennoscandia. The species is confined to springs in the north, but occurs also in lower reaches of headwater streams in central and western Europe. It becomes more rare and less abundant towards the limits of its range across Europe, showing diffusive rarity. Glacial history and climate limit the distribution of the species in the north. 2.The most important habitat characteristic for C. irrorata in Finland was the total area of helocrene habitats. Its occurrence was positively related to taxon richness of benthic macroinvertebrates, but not bryophytes. Co-occurrence of C. irrorata with other red-listed spring-dependent taxa was observed, indicating high conservation value of the springs occupied. 3.Crunoecia irrorata occurred frequently in moderately disturbed springs, indicating tolerance to human disturbance around springs. However, the effect of the disturbance on population size is not known. Forestry and water and gravel extraction are potential threats to C. irrorata, and only a few of its populations are strictly protected. Therefore, populations of C. irrorata in the boreal zone should be conserved and monitored to ensure the species' survival at the northern limits of its range. Copyright © 2007 John Wiley & Sons, Ltd. [source]