The Eurasian wheat belt (EWB) spans a region across Eastern Ukraine, Southern Russia, and Northern Kazakhstan; accounting for nearly 15% of global wheat production. We assessed landsurface conditions across the EWB during the early growing season (April –May–June; AMJ) leading up to the 2010Russianheatwave, and over a longer-term period from 2000 to 2010. A substantial reduction in early season values of the normalized difference vegetation index occurred prior to the Russianheatwave, continuing a decadal decline in early season primary production in the region. In 2010, an anomalously cold winter followed by an abrupt shift to a warmer-than-normal early growing season was consistent with a persistently negative phase of the NorthAtlanticoscillation (NAO). Regression analyses showed that early season vegetation productivity in the EWB is a function of both the winter (December –January–February; DJF) and AMJ phases of the NAO. Landsurfaceanomaliespreceding the heatwave were thus consistent with highly negative values of both the DJF NAO and AMJ NAO in 2010. Keywords: Russianheatwave, NorthAtlanticoscillation, landsurface, food security, climate change, Arctic ampli ﬁcation, MODIS
The role of the ocean, especially the sea surface temperature (SST), in regulating the NAO has been the subject of several studies (e.g., Canyan, 1992, and Kushnir, 1999). However, there is little agreement over what that role is, therefore, it still remains controversial. Nevertheless, it is widely recognized that the NAO has an important forcing role in the NorthAtlantic Ocean. In his historic study of air-sea interaction over the NorthAtlantic, Bjerkens (1964) examined the relationship between anomalies in the NorthAtlantic SLP and SST, suggesting that the interannual SST anomalies are locally driven by changes in the heat flux from the atmosphere. On the decadal timescale, however, changes in the ocean circulation, and hence ocean heat transport, may also play an important role in regulating the NAO. Some authors also suggested that there is link between the NAO index and the frequency and duration of atmospheric blocking events over the NorthAtlantic (Shutts, 1986; Hurrel, 1996, Huang et al., 2000). What is less clear, however, is whether the blocking events are causing periods of low NAO index, or if they are merely symptoms of the weakened polar vortex associated with a low NAO index. Nevertheless, the blocking is likely important in the synoptic and sub-synoptic activity over the Atlantic in affecting storm tracks.
Although tropical SST is not the dominant driver of U.S. summer SAT variability (Barlow et al. 2001), many studies have noted a connection between tropical SST forcing regions on the midlatitude summer atmosphere (e.g., Shaw and Voigt 2015; Arblaster and Alexander 2012; Pegion and Kumar 2010; Schubert et al. 2009; Lau et al. 2006; Sutton and Hodson 2005; McCabe et al. 2004; Higgins et al. 2000). Protracted La Niña events have been associated with persistent droughts, notably the large-scale midlatitude drying between 1998 and 2002 (Hoerling and Kumar 2003), the Texas drought and heatwave of 2011 (Hoerling et al. 2013), and the Dust Bowl of the 1930s (Schubert et al. 2004; Seager et al. 2005). Some studies (Ding and Wang 2005; Ding et al. 2011) suggest that model skill derives from the predict- able zonal mean component of the circumglobal tele- connection. Wang and Ting (1999) and Ting (1994) showed that nonlinear interactions among monsoonal heating-induced flows link U.S. summer climate to convective regions near Asia in the NCEP–NCAR re- analyses and GCMs. Kushnir et al. (2010) showed that warm SSTs in the tropical NorthAtlantic can exert an ‘‘upstream’’ control on SAT by weakening the sub- tropical NorthAtlantic anticyclone, driving northerly cold advection and anomalous subsidence over North America. SSTs associated with decadal modes of vari- ability, such as the Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO), can influ- ence U.S. summer SAT by modulating the Great Plains low-level jet, which brings warm, moist air from the Gulf of Mexico to the central United States (Weaver 2013).
mainly the water layer of a thickness about 2 m, where the most intense absorption of the infrared part of ra- diation occurs. Water is characterised by a poor thermal conductivity, hence it does not intensely transmit heat to the inside. The warming of deeper parts of water oc- curs due to convection and mixing of water by wind, waves and currents. With a weak impact of wind, turbu- lence transmission of heat to the inside of the reservoir is clearly limited, resulting in its increased accumula- tion close to the surface of the water table.
The air ﬂows in extratropical cyclones can be represented by the conveyor belt conceptual model e.g., Brow- ning and Roberts . Figure 1a shows the three characteristic air ﬂows: the warm conveyor belt (WCB) extending along the main cold front and rising over the warm front where it splits into lower cyclonic and upper anticyclonic turning branches; the cold conveyor belt (CCB) wrapping rearward round the cyclone to the north of the warm front; and the dry intrusion (dry air) descending from the upper troposphere toward the top of the atmospheric boundary layer. Also shown is the location of strong near surface winds attribut- able to a sting jet (SJ), a mesoscale jet of strong winds, and especially strong gusts, which occurs behind the cold front in some cyclones over a period of several hours. Mart ınez-Alvarado et al.  found that up to a third of a set of 100 winter NorthAtlantic cyclones satisﬁed the conditions for sting jets. Sustained strong surface winds occur associated with the WCB and, in mature storms, with the end of the CCB [Hewson and Neu, 2015]. The cold front wraps around the low pressure center as the system matures, and the wind direc- tion in the CCB aligns with that of the environmental westerly ﬂow and so can be associated with extreme localized winds [Browning, 2005].
Influence of wave phase difference between surface soil heat flux and soil surface temperature on landsurface energy balance closure
The sensitivity of climate simulations to the diurnal variation in surface energy budget encourages enhanced inspection into the energy balance closure failure encountered in micrometeorological experiments. The diurnal wave phases of soil surfaceheat flux and temperature are theoretically characterized and compared for both moist soil and absolute dry soil surfaces, indicating that the diurnal wave phase difference between soil surfaceheat flux and temperature ranges from 0 to π/4 for natural soils. Assuming net radiation and turbulent heat fluxes have identical phase with soil surface temper- ature, we evaluate potential contributions of the wave phase difference on the surface energy balance closure. Results show that the sum of sensible heat flux (H ) and latent heat flux (LE ) is always less than surface available energy (Rn − G0) even if all energy components are accurately measured, their footprints are strictly matched, and all cor- rections are made. The energy balance closure ratio (ε) is extremely sensitive to the ratio of soil surfaceheat flux amplitude (A4) to net radiation flux amplitude (A1), and large value of A4/A1 causes a significant failure in surface energy balance closure. An experimental case study confirms the theoretical analysis.
A very interesting finding is the fact that there has been a significant positive trend in the AO/ NAO since the 60’s, whose magnitude has no precedent in the observational and even the paleoclimate records. This change is associated with cooling over the Northwestern Atlantic and warming over the Eurasian landmass. It accounts for much of the warming trend observed in this region, whereas when the whole hemisphere is considered, AO/NAO accounts for 30% of the temperature trend (Hurrell, 1996; Thompson et al., 2000). Several causes have been suggested for the observed change in the AO/NAO, such as the increasing of greenhouse gas concentrations (Fyfe et al., 1999) and stratospheric ozone depletion (Volodin and Galin, 1999), while unforced variability remains a possibility (Wunsch, 1999). It seems that the latter is responsible of other regional changes such as stronger westerlies in the whole troposphere (Thompson and Wallace, 2000), changes in precipitation patterns into the Eurasian continent (Hurrell, 1995), changes in the storm tracks and intensity over the Atlantic (Hurrell, 1995a) or changes in the blocking frequency (Nakamura, 1996).
Here we evaluate the total heat budget, including each of the terms noted above, for the NorthAtlantic using data from the Argo profiling floats which provide continuous cover- age from 1999–2005. The winter atmospheric circulation over the NorthAtlantic Ocean is dominated by the NorthAtlanticOscillation, which during this period was predom- inantly in the positive phase (increased westerly winds), in particular in 2000, 2002, 2004–2005. There were two signif- icant negative events (decreased westerly winds), one in the latter part of 2003 and one in latter part of 2005. The associ- ated interannual variations in surfaceheat flux are typically ∼ 20 Wm −2 , compared with a mean seasonal cycle typically + / −200 Wm −2 (Fig. 3), therefore the period 1999–2006 is a reasonable period for the study of the seasonal cycle in the NorthAtlantic Ocean. To check on the validity of our ap- proach an earlier analysis based on the Ocean Circulation and Climate Advanced Model (OCCAM, Webb et al., 1998), has been used to determine the Argo sampling error in monthly mixed layer heat storage estimates (Hadfield et al., 2007a). Using OCCAM sub-sampled at the Argo positions, it was found that the mixed layer monthly heat storage, in the sub- tropical NorthAtlantic but not including the Gulf Stream, has a sampling error of 10–20 Wm −2 when averaged over a 10 ◦ × 10 ◦ area. This sampling error is sufficiently small to provide useful estimates of the heat budget over a significant fraction of the basin.
over Western Europe at lag 0 (Figure 2d). This con ﬁguration may be forced by RWB at negative lags, which leads to the intensi ﬁcation of the jet stream [Hanley and Caballero, 2012; Gómara et al., 2013]. As a consequence, cyclones encounter very favorable upper-level conditions for explosive growth [Uccellini, 1990].
Conversely, NoEC predominantly develop under a different mean ﬂow pattern (Figures 2c, 2f, and 2i) which is less transient in time. It consists of three centers of action, with negative anomalies over eastern North America and north-western Europe and a positive anomaly over south-western Greenland. Even though the structure does not resemble the NAO pattern, it projects more onto the negative phase due to the high pressure anomalies over Greenland. In this case the mean ﬂow anomalies do not appear to promote rapid intensi ﬁcation as for EC95 but to deﬂect the cyclone trajectories toward Europe due to the comparatively high pressures near Greenland (Figures 2c and 2f ). As expected from their NDR, the anomalies associated with EC (Figures 2b, 2e, and 2h) are a blend of the previous two patterns.
DOI: 10.4236/gep.2018.68010 134 Journal of Geoscience and Environment Protection Recent advances in reconstruction of the past climate with fine temporal res- olution clarified the relation between the solar cycles and the monsoon rainfall in South Oman with multiple time scales from decadal to millennial . A de- cadal variation of tropical lower stratospheric ozone and temperature has pre- viously been identified that correlates positively with the 11-year solar activity cycle. The El Niño-Southern Oscillation (ENSO) also influences lower stratos- pheric ozone and temperature .
Many of the varied mechanisms controlling stream chemistry are influenced by climatic conditions affecting either catchment inputs or within-catchment processes (Monteith et al., 2000; Neal et al., 2001). Variations in the climate of the NorthAtlantic can be characterised through the use of the NorthAtlanticOscillation (NAO) index which is the difference in sea-level atmospheric pressure between the Icelandic low and Azores high pressure systems. The pressure difference influences the climatic conditions experienced across north-western Europe, especially during the winter months. A positive NAO index in the winter translates to relatively warm and wet conditions as Atlantic frontal systems are driven across the region. Correspondingly, negative NAO winters are cold, dry and dominated by air flow from the north-east (Hurrell, 1995). Changes in the strength of the prevailing wind conditions can cause variations in the total atmospheric deposition of sea-salts, affecting fresh water chemistry (Evans et al., 2001) and associated variations in temperature have been linked
decades over the ocean basins of the Northern Hemisphere, and these changes have had a profound effect on regional distributions of surface temperature and precipitation. The changes over the North Pacific have been well documented and have contributed to increases in temperatures across Alaska and much of western North America and to decreases in sea surface temperatures over the central North Pacific. The variations over the NorthAtlantic are related to changes in the NorthAtlanticOscillation (NAO). Over the past 130 years, the NAO has exhibited considerable variability at quasi- biennial and quasi-decadal time scales, and the latter have become especially pronounced the second half of this century. Since 1980, the NAO has tended to remain in one extreme phase and has accounted for a substantial part of the observed wintertime surface warming over Europe and downstream over Eurasia and cooling in the northwest Atlantic. Anomalies in precipitation, including dry wintertime conditions over southern Europe and the Mediterranean and wetter-than-normal conditions over northern Europe and Scandinavia since 1980, are also linked to the behavior of the NAO. Changes in the monthly mean flow over the Atlantic are accompanied by a northward shift in the storm tracks and associated synoptic eddy activity, and these changes help to reinforce and maintain the anomalous mean circulation in the upper troposphere. It is important that studies of trends in local climate records, such as those from high elevation sites, recognize the presence of strong regional patterns of change associated with phenomena like the NAO.
An analysis of the mixed layer heat budget may be useful for providing insight into the mechanisms of water mass transformation which are a key component of the thermohaline circulation. During an analysis of the mixed layer heat budget, accurate determination of the ocean mixed layer is essential. Ideally, the MLD should be defined using a density criterion. However, due to the limitations of the Argo-based salinity field at the time of writing, this was not possible and instead the MLD was estimated using a temperature criterion. This may limit the accuracy of the MLD estimates, particularly in the subpolar NorthAtlantic where salinity plays an important role in stratifying the water column (Montegut et al., 2004). The Argo profiling floats sample conductivity as well as temperature, theoretically enabling salinity to be derived. However, the conductivity sensors typically exhibit significant drift caused by biofouling. Given that the floats are not recovered, calibration is not a trivial matter. Several studies have focused on this issue (Wong et al., 2003; Böhme and Send, 2005; Oka, 2005) and DMQC procedures implemented at the Argo data centres aim to improve the quality of this dataset. It is expected that in the near future (with the broad-scale implementation of these procedures) Argo floats will provide an invaluable salinity data source without the need for extensive time consuming quality control by the user.
ments, with their sum still falling short of explaining the ob- served DIC drawdown or a stoichiometric equivalent sub- surface oxygen consumption (Jenkins and Goldman, 1985; Jenkins and Doney, 2003; Johnson et al, 2010) assuming Redfield stoichiometry between organic matter production and remineralization. More recently, episodic vertical mix- ing events and lateral advection are two physical mechanisms that have been proposed to supply the surface subtropical gyres with the “missing” nutrients to explain observed ANCP (Johnson et al., 2010; Letscher et al., 2016). However, in or- der to explain the observed summertime DIC drawdown from the subtropical gyre mixed layer, these two physical mech- anisms must supply nutrients, carbon, and oxygen in non- Redfield stoichiometries. Letscher et al. (2016) reported a C-deficient, non-Redfieldian supply of inorganic carbon and nutrients within the lateral nutrient streams reaching the sub- tropical gyres, but this mechanism still falls short of explain- ing the observed DIC drawdown at the stations ALOHA and BATS, even after accounting for non-Redfield C : N : P stoi- chiometry of organic matter production. Johnson et al. (2010) observed episodic, near-monthly, vertical mixing events near Station ALOHA that supply nitrate from the nutricline up- wards into the euphotic zone to a depth of ∼ 75–100 m. They concluded that the upper 250 m is in approximate balance be- tween nutrient supply and demand and suggested that there are processes that redistribute nitrate within this region. To explain the surface DIC drawdown, these authors suggested the non-Redfieldian supply of nitrate into the mixed layer above ∼ 50 m could be carried out by large, non-flagellated
Sparks, T.H. & Yates, T.J. (1997) The effect of spring temperature on the appearance dates of British butterflies 1883–1993. Ecography,
Stenseth, N.C., Ottersen, G., Hurrell, J.W., Mysterud, A., Lima, M., Chan, K.S. et al. (2003) Studying climate effects on ecology through the use of climate indices: the NorthAtlanticOscillation, El Nino Southern Oscillation and beyond. Proceedings of the Royal Society of London, Series B: Biological Sciences, 270, 2087–2096. United Kingdom Butterfly Monitoring Scheme (2010) [WWW docu-
A few hours later, at 15:00UTC on 28 December, the turning event is essentially complete, and the winds are relatively constant, as indicated in Figure 4. It is interesting to compare model estimates from WW3- ST4m to buoy and satellite data. At this time, 2-D wave spectra are available from synthetic aperture radar (SAR) onboard ENVISAT, along the satellite track shown in Figure 11h. The SAR image is located at (39.8768N 68.6838W) as shown in Figure 11h, whereas the buoy is rather distant, 1.948 216 km away, at (40.5048N 69.2488W). The retrieved SAR data at 14:43 UTC shows a peaked spectrum in Figure 11g with maximum energy 27.1 m 2 /Hz, which corresponds reasonably well to the maximum suggested by the buoy. As shown in Figure 11e, the latter is smoothed, characteristic of the retrieval process for the Longuet-Higgins method. The directions of the spectral peaks are approximately consistent, although SAR spectrum appears to turn more than the buoy spectrum, perhaps indicative of the distance between the two measurements. Results from the simulation by WW3-ST4m, at the location of the buoy, are shown in Figure 11f. The maximum energy from the model is 24.7 m 2 /Hz, which is consistent with buoy measurements. The peak direction is also consistent with the peak direction indicated by the buoy, at about 1258. The model results also indicate a secondary peak at 2008, which is also suggested by the buoy measurements, but not evident in the SAR imagery. However, like buoy observations, SAR imagery has limitations in terms of resolution of the direc- tional wave spectra (Xie et al., 2015; Zhang et al., 2010).
estimates (Jaeschke et al., 2007) from the western tropi- cal Atlantic, representing the main route of meridional heat and surface water mass exchange (Ganachaud and Wun- sch, 2000). I note that comparison of Mg/Ca- and alkenone- derived SST records can result in uncertainties due to pos- sible differences in the seasonality and habitat depth of G. ruber pink and coccolithophorids. However, the deglacial Mg/Ca-SST record (Weldeab et al., 2006) from a site very close to that of Jaeschke et al. (2007) shows the same trend as revealed in the alkenone-based SST record (Jaeschke et al., 2007), suggesting that the latter reflects a proxy-independent thermal state of the western equatorial Atlantic. In strong contrast to the EEA SST record, the western equatorial At- lantic time series exhibits rapid SST declines and rises that are synchronous with the onset and termination of Heinrich events (Jaeschke et al., 2007) (Fig. 5), respectively. Farther to the north in the Caribbean Sea, SST reconstruction indicates surface warmth during the onset of Heinrich events (H¨uls and Zahn, 2000). The feature that emerges from the comparison is a spatially and temporally heterogeneous pattern of trop- ical Atlantic thermal response to the millennial-scale high latitude climate oscillations (Fig. 5). I suggest that the ther- mal heterogeneity of the equatorial Atlantic may be related to changes in wind fields that at a regional level could have reinforced and counteracted a possible basin-wide surface warming due to reduced northward heat transport (Chang et al., 2008; Chiang et al., 2003, 2008; Krebs and Timmer- mann, 2007; Lee et al., 2011; Lohmann, 2003). In the Gulf of Guinea, a weakening of the Guinea Current could have contributed to the EEA surface water warming. In the mod- ern climate, a southward displacement of the intertropical convergence zone (ITCZ) and a weak summer monsoon are accompanied by weakening of the Guinea Current, leading to surface water warming in the Gulf of Guinea (Philander, 1986; Schott et al., 2002). However, the abrupt strengthening of the West African monsoon at the end of Heinrich events, as indicated by the δ 18 O record (Fig. 4) (Weldeab, 2012), is not paralleled by an equally rapid decline in SST. The de- coupling of EEA SST and West African monsoon changes suggests a less prominent role of the Guinea Current.
None of the 35 species had precisely defined peak flight weeks in all 34 years between 1976 and 2009. It can, for example, be difficult to precisely identify a peak flight week if similar numbers of butterflies are counted in each of two consecutive weeks. However, abundant univoltine species with shorter flight seasons generated more accurately defined peak flight weeks in more years than species that were bivoltine, less abundant or had a longer flight season. Accurate determination of the peak flight week for some bivoltine species was reduced if one generation was quite small, or by the presence, in some years, of a third generation. Voltinism is also affected by latitude and thus a species can be bivoltine in southern Britain and univoltine further north. Thus, high-quality datasets suitable for analysis of flight timing are available for only a rather limited number of butterfly species, of which most are univoltine and only two are bivoltine.
The alpine region exhibits the strongest interannual vari- ability of winter precipitation in Europe. In this paper an at- tempt is made to relate this variability to the dominant large- scale modes of climate variability in the Northern Hemi- sphere. The Arctic Oscillation and the NorthAtlantic Os- cillation are found to present only a weak correlation with winter alpine precipitation, regardless of aggregation scales, the use of time lags or the filtering of more extreme phases of the climate patterns. The East Atlantic-West Russia shows a significant negative correlation with precipitation anomalies but only for the first part of the winter season. Only some significant, yet small, trends are observed in a small region of the Alpine Eastern sector, that could suggest a small de- crease in precipitation totals and an increase in short-term dry anomalies in this area (Fig. 7).