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Abstract Much of the early research which now underpins tunnel fire safety design was carried out experimentally, using small scale ducts. This paper reviews such experiments, mostly carried out in the 1960s, 1970s, and 1980s, highlighting the assumptions and limitations of the early studies, which may have been forgotten as the equations developed have been applied in practice in the subsequent years. The review covers three primary topics; fire propagation under ‘turbulent slug flow’ conditions, stratification & flame spread, and backlayering & critical ventilation velocity. [ABSTRACT FROM AUTHOR]

We have analyzed time series of solar data together with the atmospheric and ionospheric measurements for solar cycles 19 till 23 according to particular data availability. For the analyses we have used long term data with 1-day sampling. By mean of Continuous Wavelet Transform (CWT) we have found common spectral domains within solar and atmospheric and ionospheric time series. Further we have identified terms when particular pairs of signals show high coherence applying Wavelet Transform Coherence (WTC). Despite wide oscillation ranges detected in particular time series CWT spectra we found only limited domains with high coherence by mean of WTC. Wavelet Transform Coherence reveals significant high power domains with stable phase difference for periods 1 month, 2 months, 6 months, 1 year, 2 years and 3–4 years between pairs of solar data and atmospheric and ionospheric data. The occurence of the detected domains vary significantly during particular solar cycle (SC) and from cycle to the following one. It indicates the changing solar forcing and/or atmospheric sensitivity with time. [ABSTRACT FROM AUTHOR]

Maintaining a strong antioxidant system is essential for preventing drought-induced oxidative stress. Thus, in the present study we investigated the role of some non-enzymic and enzymic antioxidants in desiccation tolerance of Haberlea rhodopensis . The effects of high light upon desiccation on antioxidant capacity was estimated by comparing the response of shade and sun plants. The significant enhancement of the antioxidant capacity at 8% RWC corresponded to an enormous increase in flavonoid content. The important role of ascorbate-glutathione cycle in overcoming oxidative stress during drying of H. rhodopensis was established. The antioxidant capacity increased upon dehydration of both shade and sun plants but some differences in non-enzymatic and enzymatic antioxidants were observed. Investigations on the role of polyphenols in desiccation tolerance are scarce. In the present study the polyphenol profiles (fingerprints) of the resurrection plant Haberlea rhodopensis , including all components of the complex are obtained for the first time. It was clarified that the polyphenol complex of H. rhodopensis includes only two types of glycosides - phenylethanoid glucosides and hispidulin 8-C-glucosides. Upon desiccation the polyphenol content increase and the main role of phenylethanoid glucosides in the protection of H. rhodopensis was revealed. [ABSTRACT FROM AUTHOR]

Abstract: The correlation between geomagnetic activity and the sunspot number in the 11-year solar cycle exhibits long-term variations due to the varying time lag between the sunspot-related and non-sunspot related geomagnetic activity, and the varying relative amplitude of the respective geomagnetic activity peaks. As the sunspot-related and non-sunspot related geomagnetic activity peaks are caused by different solar agents, related to the solar toroidal and poloidal fields, respectively, we use their variations to derive the parameters of the solar dynamo transforming the poloidal field into toroidal field and back. We find that in the last 12 cycles the solar surface meridional circulation varied between 5 and 20m/s (averaged over latitude and over the sunspot cycle), the deep circulation varied between 2.5 and 5.5m/s, and the diffusivity in the whole of the convection zone was ∼108 m2/s. In the last 12 cycles solar dynamo has been operating in moderately diffusion dominated regime in the bulk of the convection zone. This means that a part of the poloidal field generated at the surface is advected by the meridional circulation all the way to the poles, down to the tachocline and equatorward to sunspot latitudes, while another part is diffused directly to the tachocline at midlatitudes, “short-circuiting” the meridional circulation. The sunspot maximum is the superposition of the two surges of toroidal field generated by these two parts of the poloidal field, which is the explanation of the double peaks and the Gnevyshev gap in sunspot maximum. Near the tachocline, dynamo has been operating in diffusion dominated regime in which diffusion is more important than advection, so with increasing speed of the deep circulation the time for diffusive decay of the poloidal field decreases, and more toroidal field is generated leading to a higher sunspot maximum. During the Maunder minimum the dynamo was operating in advection dominated regime near the tachocline, with the transition from diffusion dominated to advection dominated regime caused by a sharp drop in the surface meridional circulation which is in general the most important factor modulating the amplitude of the sunspot cycle. [Copyright &y& Elsevier]

Summary: The changes in some proteins involved in the light reactions of photosynthesis of the resurrection plant Haberlea rhodopensis were examined in connection with desiccation. Fully hydrated (control) and completely desiccated plants (relative water content (RWC) 6.5%) were used for thylakoid preparations. The chlorophyll (Chl) a to Chl b ratios of thylakoids isolated from control and desiccated leaves were very similar, which was also confirmed by measuring their absorption spectra. HPLC analysis revealed that β-carotene content was only slightly enhanced in desiccated leaves compared with the control, but the zeaxanthin level was strongly increased. Desiccation of H. rhodopensis to an air-dried state at very low light irradiance led to a little decrease in the level of D1, D2, PsbS and PsaA/B proteins in thylakoids, but a relative increase in LHC polypeptides. To further elucidate whether the composition of the protein complexes of the thylakoid membranes had changed, we performed a separation of solubilized thylakoids on sucrose density gradients. In contrast to spinach, Haberlea thylakoids appeared to be much more resistant to the same solubilization procedure, i.e. complexes were not separated completely and complexes of higher density were found. However, the fractions analyzed provided clear evidence for a move of part of the antenna complexes from PSII to PSI when plants became desiccated. This move was also confirmed by low temperature emission spectra of thylakoids. Overall, the photosynthetic proteins remained comparatively stable in dried Haberlea leaves when plants were desiccated under conditions similar to their natural habitat. Low light during desiccation was enough to induce a rise in the xanthophyll zeaxanthin and β-carotene. Together with the extensive leaf shrinkage and some leaf folding, increased zeaxanthin content and the observed shift in antenna proteins from PSII to PSI during desiccation of Haberlea contributed to the integrity of the photosynthetic apparatus, which is important for rapid recovery after rehydration. [Copyright &y& Elsevier]

Abstract: General atmospheric circulation is the system of atmospheric motions over the Earth on the scale of the whole globe. Two main types of circulation have been identified: zonal – characterized by low amplitude waves in the troposphere moving quickly from west to east, and meridional with stationary high amplitude waves when the meridional transfer is intensified. The prevailing type of circulation is related to global climate. Based on many years of observations, certain “circulation epochs” have been defined when the same type of circulation prevails for years or decades. Here we study the relation between long-term changes in solar activity and prevailing type of atmospheric circulation, using NAO index reconstructed for the last four centuries as a proxy for large-scale atmospheric circulation. We find that when the southern solar hemisphere is more active, increasing solar activity in the secular solar cycle results in increasing zonality of the circulation, while when the northern solar hemisphere is more active, increasing solar activity increases meridional circulation. In an attempt to explain the observations, we compare the short-term reaction of NAO and NAM indices to different solar drivers: powerful solar flares, high speed solar wind streams, and magnetic clouds. [Copyright &y& Elsevier]

Abstract: The relationship between the level of UV-B-induced and/or UV-B-absorbing compounds and stress tolerance of barley seedlings (Hordeum vulgare L. cv. Alfa) was investigated. A physiological response to UV-B irradiation was evaluated by measuring the oxygen evolution rate and chlorophyll fluorescence. UV-B irradiation led to an increase of the amount of UV-B absorbing compounds, including flavonoids, measured in acidified methanol extract at 300nm and of UV-B induced compounds, with maximum absorbance at 438nm, extracted in 0.1% trichloracetic acid. The content of free proline, malondialdehide and H2O2 increased as a result of 4 days treatment with 150mM NaCl, KCl or NaNO3. Salt pretreatment resulted in considerable decrease of the level of UV-induced and UV-B absorbing compounds measured 24h after UV-B irradiation. In the meantime chlorophyll fluorescence parameters and oxygen evolution in salt pretreated seedlings were less affected by UV-B in comparison to the control. Damaging effect of UV-B measured by the MDA and H2O2 generation and electron transport activity corresponded to the increased levels of UV-B induced and UV-B absorbing compounds. We do not necessarily exclude UV-inducing compounds from an important role in overall UV-B protection but the data presented here showed that the accumulation of these compounds could be a consequence of stress-induced damage to the cells and probably they may serve as stress markers. [Copyright &y& Elsevier]

Abstract: Magnetic clouds, characterized by high magnetic field magnitude, low proton temperature and plasma beta, and a smooth rotation in the magnetic field direction, cause strong geomagnetic disturbances. In the present paper we study the impact of magnetic clouds on the middle atmosphere and geomagnetic disturbances. We find that the effects of magnetic clouds depend on both the phase of the quasibiennial oscillations of equatorial stratospheric winds, and on the handedness, or direction of rotation, of the magnetic field in the cloud. Strongest influence on the stratosphere both in the Northern and Southern hemispheres has left-handed magnetic clouds in QBO Easterly phase. Effects of magnetic clouds are seen in the mesopause region as well, and their effects on the neutral winds and geomagnetic disturbances also depend on QBO phase and the handedness of the clouds, being strongest again for left-handed clouds in QBO Easterly phase. [Copyright &y& Elsevier]

Earlier studies have demonstrated a relation between long-term changes in the Earth''s rotation rate and the prevalence of zonal or meridional types of circulation. The results, however, have been confined to the 20th century and to the Northern hemisphere. In the present paper we compare the long-term changes in the length of the day (LOD) and the temperature contrast between the equator and the pole in the Northern and the Southern hemispheres as an indirect measure for the zonality of the atmospheric circulation. In the 20th century in the Northern hemisphere we find a high negative correlation between the rotation rate and the equator/pole temperature contrast, while in the 19th century the correlation is positive. For the Southern hemisphere, the situation is opposite. The correlation changes when the North–South asymmetry of solar activity also changes sign. The decadal changes in LOD are shown to be related to the changes in the North–South asymmetry of solar equatorial rotation rate supposedly induced by planetary-driven changes in the angular momentum of the solar system, with both quantities showing pronounced periodicities and high squared coherence at 47 years. It is hypothesized that decadal changes in LOD are driven by core-mantle coupling processes regulated by solar wind transferring solar magnetic fields and angular momentum modulated by planetary influences. The atmospheric circulation in the Northern and Southern hemispheres is found to be different not only on decadal time-scales but also in the 11-year solar cycle, and different in even and odd cycles. While long-term changes in geomagnetic activity closely follow sunspot activity changes, the correlation between the two in the 11-year cycle has been decreasing in the last century with the increase of the North–South solar activity asymmetry which modulates also the asymmetry of galactic cosmic rays flux considered a candidate mediator between solar activity and climate. [Copyright &y& Elsevier]

This brief introductory review of some recent developments in atmosphere–ionosphere science is written for the “Vertical Coupling Special Issue” that is motivated by the 5th IAGA/ICMA/SCOSTEP Workshop on Vertical Coupling in the Atmosphere–Ionosphere System. Basic processes of vertical coupling in the atmosphere–ionosphere system are discussed, focusing on the effects of internal waves, such as gravity waves and solar tides, sudden stratospheric warmings (SSWs), and of solar activity on the structure of the atmosphere. Internal waves play a crucial role in the current state and evolution of the upper atmosphere–ionosphere system. SSW effects extend into the upper atmosphere, producing changes in the thermospheric circulation and ionospheric disturbances. Sun, the dominant energy source for the atmosphere, directly impacts the upper atmosphere and modulates wave-induced coupling. The emphasis is laid on the most recent developments in the field, while giving credits to older works where necessary. Various international activities in atmospheric vertical coupling, such as SCOSTEP's ROSMIC project, and a brief contextual discussion of the papers published in the special issue are presented. [ABSTRACT FROM AUTHOR]

Abstract: From the leaves of barley seedlings (Hordeum vulgare L. cv. Alfa) UV-B induced compounds, with maximum absorbance at 438nm (A438) were extracted. The relationship between the level of UV-B induced compounds and UV-B tolerance of barley seedlings was investigated. The level of these compounds depended on the time of UV-B irradiation. They increased 4h after UV-B treatment, reached maximum after 24h and then declined. Contrary, the syntheses of UV-absorbing compounds extracted in acidified methanol continued for a long period after UV exposure and after 120h the values of A300 are higher. The content of UV-induced compounds enhanced in the plants treated with proline before UV-B irradiation and decreased as a result of NaCl pretreatment in a concentration depending manner. A physiological response to UV-B irradiation was evaluated by measuring the oxygen evolution rate, chlorophyll fluorescence and chlorophyll/carotenoids ratio. No correlation was found between the level of A438 and UV-B tolerance of barley seedlings. It is possible these compounds to play a subtle role in plant UV-B protection than simple UV-B screening or to serve as stress markers. [Copyright &y& Elsevier]

Haberlea rhodopensis is a chlorophyll-retaining resurrection plant, which can survive desiccation to air dry state under both low light and sunny environments. Maintaining the integrity of the membrane during dehydration of resurrection plants is extremely important. In the present study, the diffusion model was improved and used for a first time to evaluate the changes in ion leakage through different cellular compartments upon desiccation of H. rhodopensis and to clarify the reasons for significant increase of electrolyte leakage from dry leaves. The applied diffusion approach allowed us to distinguish the performance of plants subjected to dehydration and subsequent rehydration under different light intensities. Well-hydrated (control) shade plants had lower and slower electrolyte leakage compared to control sun plants as revealed by lower values of phase amplitudes, lower rate constants and ion concentration. In well-hydrated and moderately dehydrated plants (50% relative water content, RWC) ion efflux was mainly due to leakage from apoplast. The electrolyte leakage sharply increased in severely desiccated leaves (8% RWC) from both sun and shade plants mainly due to ion efflux from symplast. After 1 day of rehydration the electrolyte leakage was close to control values, indicating fast recovery of plants. We suggest that the enhanced leakage in air-dried leaves should not be considered as damage but rather as a survival mechanism based on a reversible modification in the structure of cell wall, plasma membrane and alterations in vacuolar system of the cells. However, further studies should be conducted to investigate the changes in cell wall/plasma membrane to support this conclusion. [ABSTRACT FROM AUTHOR]

In the present study, we examined the photoprotective mechanisms of the homoiochlorophyllous desiccation-tolerant (DT) Haberlea rhodopensis Friv. (Gesneriaceae) during the desiccation–rehydration cycle in its natural understory shaded and sunny habitats within drought prone regions. The integration of classical analysis of chlorophyll fluorescence with a detailed analysis of energy partitioning showed a re-adjustment in the function and extent of the different components of energy management in photosystem II (PSII) depending on the degree of dehydration. At mild dehydration, the non-photochemical quenching by active centres (NPQ) played a relevant role in preventing photoinhibition, while under the photoinhibitory conditions occurring when dehydration was severe, the light-dependent quenching by inactive centres provided strong photoprotection. These analyses of the photosynthetic and PSII functionality together with measurements of carotenoid changes showed that the photoprotective mechanisms of this resurrection species were also affected by growth irradiance. Plants growing in understory shaded habitats were mainly protected against dehydration by the mechanism of thermal re-emission by inactive PSII reaction centres together with the relevant contribution of an operative xanthophyll-cycle involved in a quenching process triggered by dehydration itself. Conversely, plants growing in sunny open environments relied more on the quenching mechanism in the light-harvesting antennae. One additional role of carotenoids, in particular of β-carotene, in dehydration tolerance of H. rhodopensis may well be quenching of ROS, a mechanism that could occur in homoiochlorophyllous resurrection plants as a consequence of the retained chlorophylls and photosynthetic apparatus, especially when plants grow in open sunny habitats. [ABSTRACT FROM AUTHOR]

The resurrection plant, Haberlea rhodopensis can survive nearly total desiccation only in its usual low irradiation environment. However, populations with similar capacity to recover were discovered recently in several sunny habitats. To reveal what kind of morphological, structural and thylakoid-level alterations play a role in the acclimation of this low-light adapted species to high-light environment and how do they contribute to the desiccation tolerance mechanisms, the structure of the photosynthetic apparatus, the most sensitive component of the chlorophyll-retaining resurrection plants, was analyzed by transmission electron microscopy, steady state low-temperature fluorescence and two-dimensional Blue-Native/SDS PAGE under desiccation and rehydration. In contrast to the great differences in the morphology of plants, the ultrastructure and the organization of thylakoids were surprisingly similar in well-hydrated shade and sun populations. A high ratio of photosystem (PS)I binding light harvesting complex (LHC)II, important in low- and fluctuating light environment, was characteristic to both shade and sun plant, and the ratios of the main chlorophyll–protein complexes were also similar. The intensive protective mechanisms, such as shading by steep leaf angle and accumulation of protective substances, probably reduced the light intensity at the chloroplast level. The significantly increased ratio of monomer to oligomer antennae in well-hydrated sun plants may be connected with the temporary high light exposure of chloroplasts. During desiccation, LHCII was removed from PSI and part of PSII supercomplexes disassembled with some loss of PSII core and LHCII. The different reorganization of antennae, possibly connected with different quenching mechanisms, involved an increased amount of monomers in shade plants but unchanged proportion of oligomers in sun plants. Desiccation-induced responses were more pronounced in sun plants which also had a greater capacity to recover due to their stress-acclimated attitude. [ABSTRACT FROM AUTHOR]

Summary: The effects of short-term darkening and methyl jasmonate (MeJA) on cotyledon senescence were studied 24h after transfer of intact 7-day-old Cucurbita pepo (zucchini) seedlings to darkness or spraying with 100μM MeJA. The jasmonate inhibitory effect on chlorophyll content and chloroplast transcriptional activity was stronger compared with darkness. Further, MeJA reduced the photosynthetic rate whereas darkness did not affect photosynthesis. Neither stress factor affected the photochemical quantum efficiency of photosystem II (PSII) estimated by the variable fluorescence (F v)/maximal fluorescence (F m) ratio, suggesting the existence of mechanisms protecting the functional activity of PSII at earlier stages of senescence, thus making this parameter more stable compared to others used to quantify senescence. Both stress factors caused a decrease in the content of physiologically active cytokinins, especially trans-zeatin (Z), with the jasmonate effect being much more pronounced when compared to darkness. Our results indicate that MeJA is a more potent inducer of senescence in zucchini cotyledons, at least within the relatively short period of the 24h treatment. This is likely due to its stronger down-regulatory effect on the levels of physiologically active cytokinins. [Copyright &y& Elsevier]

Summary: The photosynthetic changes evaluated by oxygen evolution, chlorophyll fluorescence, photoacoustics, and delayed fluorescence (DF) were studied in leaves of grown in vitro for 8 weeks grapevine plants (Vitis vinifera) infected by grapevine leafroll-associated virus 3 (GLRaV-3). The infected leaves were characterized during the viral infection without visible disease symptoms. The symptomless infection led to a decrease in plant biomass. The non-photochemical fluorescence quenching, qN, declined, whereas the photochemical quenching, qP, and the Chl a/b ratio were not significantly affected. Photoacoustic and oxygen evolution measurements showed that the energy storage and oxygen evolution rate decreased in the infected leaves. Enhanced alternative electron sinks during the symptomless viral infection were also estimated. The changes in fluorescence and DF temperature curves demonstrated an enhanced stability of the thylakoid membranes in the infected leaves. This effect was clearly expressed at high actinic light intensities. The viral infected in vitro grown grapevine plants were used in the present study as a simplified model system that allow to avoid the involvement of different environmental factors that could interfere with the GLRaV infection and the virus–grapevine interactions. Thus, the ‘pure’ impact of the viral infection on photosynthesis could be investigated. [Copyright &y& Elsevier]

• Cold acclimated fresh leaves of H. rhodopensis survive subzero temperatures. • Newly observed narrow epidermal channels contribute to the fast water loss upon frost stress. • Decrease in the efficiency of excitation energy transfer to reaction centers is essential for frost survival. • Survival of frost conditions is also based on desiccation-like readjustment of the photosynthetic apparatus. Haberlea rhodopensis is unique among homoiochlorophyllous resurrection plants with its ability to tolerate also low temperatures at temperate climate. This study was carried out to elucidate the response and acclimation ability of photosynthetic apparatus to cold and the capacity to tolerate freezing temperatures. Cold acclimated plants experienced short-term freezing conditions under controlled-environment in climatic chamber and also long-term subzero winter temperatures in an ex-situ natural environment. Our results indicated strong freezing tolerance after cold acclimation. In fact, fresh leaves were exposed to and survived freezing stress under both controlled and ex-situ conditions, thus confirming their appropriate cold acclimation. Freezing temperatures induced desiccation of leaves and the corresponding ultrastructural changes in mesophyll cells under ex situ environmental conditions. However, while the complete rearrangement in the cells commenced at 20 % RWC under drought stress, this process started already at 60 % RWC under freezing conditions. The presence of epidermal channels on both leaf sides was observed and their role for the fast water loss is proposed. It was found that freezing-induced desiccation, reversible downregulation of photosynthesis, readjustments in the abundance/organization of the pigment protein complexes and the main photosynthetic proteins together with increased thermal energy dissipation during chilling and freezing temperatures enable plants to survive harsh winter conditions and their fast recovery with the onset of spring. Low temperature responses are discussed in comparison to desiccation-induced changes to point out both common and specific features. [ABSTRACT FROM AUTHOR]