Recent seasonal asymmetric changes in the NAO (a marked summer decline and increased winter variability) and associated changes in the AO and Greenland Blocking Index

2014 ◽  
Vol 35 (9) ◽  
pp. 2540-2554 ◽  
Author(s):  
Edward Hanna ◽  
Thomas E. Cropper ◽  
Philip D. Jones ◽  
Adam A. Scaife ◽  
Rob Allan
Keyword(s):  
Summer Decline ◽  
Blocking Index

scholarly journals Blocking Detection Based on Synoptic Filters

2011 ◽  
Vol 2011 ◽  
pp. 1-11 ◽  
Author(s):  
Bernd Schalge ◽  
Richard Blender ◽  
Klaus Fraedrich
Keyword(s):  
Case Studies ◽  
Southern Hemisphere ◽  
Geopotential Height ◽  
Height Anomaly ◽  
Geopotential Height Anomaly ◽  
Minimum Duration ◽  
Additional Filter ◽  
Blocking Index

The Tibaldi-Molteni blocking index is supplemented by additional filter criteria to eliminate cut-off lows and subsynoptic structures. We introduce three blocking filters and analyse their sensitivities: (i) a quantile filter requiring a minimum geopotential height anomaly to reject cut-off lows, (ii) an extent filter to extract scales above a minimum zonal width, and (iii) a persistence filter to extract events with a minimum duration. Practical filter application is analysed in two case studies and the blocking climatologies for the Northern and the Southern Hemisphere.

scholarly journals Anomalous blocking over Greenland preceded the 2013 extreme early melt of local sea ice

2017 ◽  
Vol 59 (76pt2) ◽  
pp. 181-190 ◽  
Author(s):  
Thomas J. Ballinger ◽  
Edward Hanna ◽  
Richard J. Hall ◽  
Thomas E. Cropper ◽  
Jeffrey Miller ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Regional Climate ◽  
Regional Climate Change ◽  
Circulation Pattern ◽  
The Arctic ◽  
Labrador Sea ◽  
First Year ◽  
Tropospheric Circulation ◽  
Blocking Index

ABSTRACTThe Arctic marine environment is undergoing a transition from thick multi-year to first-year sea-ice cover with coincident lengthening of the melt season. Such changes are evident in the Baffin Bay-Davis Strait-Labrador Sea (BDL) region where melt onset has occurred ~8 days decade−1 earlier from 1979 to 2015. A series of anomalously early events has occurred since the mid-1990s, overlapping a period of increased upper-air ridging across Greenland and the northwestern North Atlantic. We investigate an extreme early melt event observed in spring 2013. (~6σ below the 1981–2010 melt climatology), with respect to preceding sub-seasonal mid-tropospheric circulation conditions as described by a daily Greenland Blocking Index (GBI). The 40-days prior to the 2013 BDL melt onset are characterized by a persistent, strong 500 hPa anticyclone over the region (GBI >+1 on >75% of days). This circulation pattern advected warm air from northeastern Canada and the northwestern Atlantic poleward onto the thin, first-year sea ice and caused melt ~50 days earlier than normal. The episodic increase in the ridging atmospheric pattern near western Greenland as in 2013, exemplified by large positive GBI values, is an important recent process impacting the atmospheric circulation over a North Atlantic cryosphere undergoing accelerated regional climate change.

scholarly journals The Seasonal Cycle of Blocking and Associated Physical Mechanisms in the Australian Region and Relationship with Rainfall

2013 ◽  
Vol 141 (12) ◽  
pp. 4534-4553 ◽  
Author(s):  
M. J. Pook ◽  
J. S. Risbey ◽  
P. C. McIntosh ◽  
C. C. Ummenhofer ◽  
A. G. Marshall ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Seasonal Cycle ◽  
Seasonal Temperature ◽  
Ocean Fronts ◽  
Temperature Changes ◽  
Physical Mechanisms ◽  
Australian Region ◽  
Continental Antarctica ◽  
Positive Correlations ◽  
Blocking Index

Abstract The seasonal cycle of blocking in the Australian region is shown to be associated with major seasonal temperature changes over continental Antarctica (approximately 15°–35°C) and Australia (about 8°–17°C) and with minor changes over the surrounding oceans (below 5°C). These changes are superimposed on a favorable background state for blocking in the region resulting from a conjunction of physical influences. These include the geographical configuration and topography of the Australian and Antarctic continents and the positive west to east gradient of sea surface temperature in the Indo-Australian sector of the Southern Ocean. Blocking is represented by a blocking index (BI) developed by the Australian Bureau of Meteorology. The BI has a marked seasonal cycle that reflects seasonal changes in the strength of the westerly winds in the midtroposphere at selected latitudes. Significant correlations between the BI at Australian longitudes and rainfall have been demonstrated in southern and central Australia for the austral autumn, winter, and spring. Patchy positive correlations are evident in the south during summer but significant negative correlations are apparent in the central tropical north. By decomposing the rainfall into its contributions from identifiable synoptic types during the April–October growing season, it is shown that the high correlation between blocking and rainfall in southern Australia is explained by the component of rainfall associated with cutoff lows. These systems form the cyclonic components of blocking dipoles. In contrast, there is no significant correlation between the BI and rainfall from Southern Ocean fronts.

scholarly journals Southern Hemisphere Blocking Onsets Associated with Upper-Tropospheric Divergence Anomalies

2005 ◽  
Vol 62 (5) ◽  
pp. 1614-1625 ◽  
Author(s):  
F. Javier Sáez de Adana ◽  
Stephen J. Colucci
Keyword(s):  
Southern Hemisphere ◽  
Nonlinear Effect ◽  
Local Development ◽  
Relative Vorticity ◽  
Convective Activity ◽  
Early Winter ◽  
Horizontal Advection ◽  
Blocking Activity ◽  
The Tropics ◽  
Blocking Index

Abstract Upper-tropospheric divergence anomalies and divergence tendencies prior to and during the onset of blocking have been investigated for selected cases over the Southern Hemisphere in search of links between the upper-tropospheric response to tropical convective activity and the onset of blocking in midlatitudes. Climatologies of blocking, defined by an objective index, and divergence are established for the Southern Hemisphere and the southern Pacific, respectively. Relative blocking frequency versus longitude reveals a region of maximum blocking activity between 160°E and 75°W. Blocking frequencies for each ENSO phase indicate a shift toward the late austral fall and early winter during the warm phase, whereas during the cold and neutral phases the highest frequencies are in June and July, respectively. Composites of area-averaged divergence anomalies for the selected blocking cases reveal more anomalous divergence than during nonblocking periods over the blocking regions and the immediate upstream regions in midlatitudes. A full divergence tendency equation is utilized to diagnose the local development of divergence preceding the onset of blocking. Results indicate that divergence tendencies over midlatitudes in the block-onset region were forced primarily by horizontal advection, ageostrophic relative vorticity, and a nonlinear effect. In the region directly upstream from the block-onset region, ageostrophic relative vorticity had the greatest contribution followed by the horizontal advection. In the Tropics, divergence tendencies appear to be driven primarily by horizontal advection. Correlations of calculated divergence tendencies with the blocking index suggest that ageostrophic vorticity may locally generate divergence that in turn may force anticyclonic vorticity associated with blocking. Lag correlations with a blocking index during blocking reveal the importance of horizontal advection in driving divergence anomalies, implying divergence-induced vorticities, toward the incipient block.

Response selectivity of neurons in area MT of the macaque monkey during reversible inactivation of area V1

1992 ◽  
Vol 67 (6) ◽  
pp. 1437-1446 ◽  
Author(s):  
P. Girard ◽  
P. A. Salin ◽  
J. Bullier
Keyword(s):  
Receptive Field ◽  
Macaque Monkey ◽  
Direction Selectivity ◽  
Area 17 ◽  
Visual Responses ◽  
Area Mt ◽  
Reversible Inactivation ◽  
Mt Neurons ◽  
Preferred Direction ◽  
Blocking Index

1. Behavioral results in the monkey and clinical studies in human show remarkable residual visual capacities after a lesion of area V1. Earlier work by Rodman et al. demonstrated that visual activity can be recorded in the middle temporal area (MT) of the macaque monkey several weeks after a complete lesion of V1. These authors also tested the effect of a reversible block of area V1 on the visual responses of a small number of neurons in area MT and showed that most of these cells remain visually responsive. From the results of that study, however, it is difficult to assess the contribution of area 17 to the receptive-field selectivity of area MT neurons. To address this question, we have quantitatively measured the effects of a reversible inactivation of area 17 on the direction selectivity of MT neurons. 2. A circular part of the opercular region of area V1 was reversibly inactivated by cooling with a Peltier device. A microelectrode was positioned in the lower layers of V1 to control the total inactivation of that area. Eighty percent of the sites recorded in the retinotopically corresponding region of MT during inactivation of V1 were found to be visually responsive. The importance of the effect was assessed by calculating the blocking index (0 for no effect, 1 for complete inactivation). Approximately one-half of the quantitatively studied neurons gave a blocking index below 0.6, illustrating the strong residual responses recorded in many neurons. 3. Receptive-field properties were examined with multihistograms. It was found that, during inactivation of V1, the preferred direction changed for most neurons but remained close to the preferred direction or to its opposite in the control situation. During inactivation of V1, the average tuning curve of neurons became broader mostly because of strong reductions in the response to directions close to the preferred and nonpreferred. Very little change was observed in the responses for directions at 90 degrees to the optimal. These results are consistent with a model in which direction selectivity is present without an input from V1 but is reinforced by the spatial organization of this excitatory input. 4. Residual responses were found to be highly dependent on the state of anesthesia because they were completely abolished by the addition of 0.4-0.5% halothane to the ventilation gases. Finally, visual responses were recorded in area MT several hours after an acute lesion of area 17.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Response of birch (Betula pendula Roth) phytophages to liming

2008 ◽  
Vol 54 (No. 12) ◽  
pp. 572-578
Author(s):  
E. Kula
Keyword(s):  
Betula Pendula ◽  
Positive Response ◽  
Dolomitic Limestone ◽  
Extent Of Damage ◽  
Summer Decline ◽  
Higher Doses

: In the course of 2004–2007, the effects of compensation liming at the application dose of 1.5–3–6 t/ha dolomitic limestone on the elimination or activation of phytophages or other types of damage resulting in the loss of assimilatory organs did not become evident yet. A shift was noted in the fluctuation expressed indirectly by the extent of damage to the assimilatory area in feeding caused by an undetermined hymenopterous larva (summer increase), weevils (spring and summer decline and increase in 2007), <I>Coleophora serratella</I> (decline), <I>Eriocrania</I> sp. (increase), mites <I>Acalitus rudis</I> (increase), <I>Eriophyes leionotus</I> (increase in 2006–2007). Only signs of a positive response to higher doses of dolomitic limestone characterized the mite <I>Eriophyes leionotus</I>.

Effects of High Temperature on Survival of the Giant Scallop

1958 ◽  
Vol 15 (6) ◽  
pp. 1189-1211 ◽  
Author(s):  
L. M. Dickie
Keyword(s):  
High Temperature ◽  
Temperature Acclimation ◽  
Direct Result ◽  
Acclimation Temperature ◽  
Lethal Temperature ◽  
Temperature Changes ◽  
Naturally Occurring ◽  
Special Circumstances ◽  
Summer Decline ◽  
Sudden Temperature Change

Upper lethal temperatures of scallops are raised 1 °C. by each increase of 5 °C. in acclimation temperature. Acclimation upwards is fairly rapid (average 1.7 °C. per day over part of the range). Loss of acclimation to high temperature is slow, and appears to take as long as 3 months. There is a winter-to-summer decline in lethal temperature. It appears that naturally occurring water temperatures over 23.5 °C. will be lethal to scallops and directly responsible for mortalities. Temperatures over 21 °C. may also be a direct cause of mortalities but only in special circumstances could mortalities occur as a direct result of temperatures below this. In the "sub-lethal" temperature range, sudden temperature changes upward or downward may so reduce scallop mobility as to make them easier prey to enemies. In this way sudden temperature change could be an indirect cause of increased mortality.

An experimental study of the summer decline in a Daphnia population

1985 ◽  
Vol 22 (5) ◽  
pp. 3131-3136
Author(s):  
Petter Larsson ◽  
Geir Johnsen ◽  
Andreas L. Steigen
Keyword(s):  
Experimental Study ◽  
Daphnia Population ◽  
Summer Decline

FLUCTUATIONS IN NUMBERS OF ADULT BLACK FLIES (DIPTERA: SIMULIIDAE) IN DEEP RIVER, ONTARIO

1972 ◽  
Vol 104 (9) ◽  
pp. 1465-1470 ◽  
Author(s):  
W. F. Baldwin ◽  
H. P. Gross
Keyword(s):  
Late Summer ◽  
Weather Conditions ◽  
Control Site ◽  
Black Flies ◽  
Small Stream ◽  
Local Species ◽  
Summer Decline ◽  
The Town ◽  
Light Forest ◽  
Control Trap

AbstractAdult black flies were trapped at the townsite of Deep River from the early emergence of Prosimulium spp. (approx. 21 May) through to the late summer decline of Simulium spp. (in August). "Sticky" traps employing CO2 as an attractant were located at five sites throughout the town; in addition a trap was positioned at a "control" site outside the town limits near a heavily forested area. The overall numbers increased rapidly in early June, remaining at high levels until the first week in July, by which time over 110,000 flies had been captured. The numbers of flies recovered both within and outside the town fluctuated widely with weather conditions, seemingly influenced by precipitation. In the town, three centrally located traps captured only half as many adults as two traps near the southerly limits, where a small stream flowed through light forest. The control trap showed that black flies were at least 10 times more plentiful outside Deep River. Three insecticide applications did not have any measurable effect on fly numbers. The predominant local species is Simulium venustum Say.

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