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School discontinuation in Finland is more common among the Finnish Roma than among the population as a whole. We lack knowledge of the perspective of those of the Roma, representing a minority inside a minority, who have left compulsory school without a leaving certificate. Within a study about school experiences of imprisoned early school leavers in Finland we had six participants with a Finnish Roma background, whose experiences of relatedness, and frustration of it, we examine in this paper. We conducted narrative interviews with the participants, applying a co-operative narrative interpretation to the meanings of what was told. After the field process, we interpreted the narrative accounts focusing on experiences of relatedness, and how relationships with people in the school environment affected the participants’ sense of belonging together with the people in the school environment. Frustration of relatedness was identified at three levels. Firstly, at a general, life condition level, cultural prejudice manifested itself as a sense of not being accepted and respected as an equal with other people, the situation creating a constant need to cope with outspoken prejudices. Secondly, at a contextual-specific level in the school environment, we identified experiences of being rejected by peers and their parents, as well as some of the teachers. This was linked with a sense of loneliness and detachment from other people in the school environment. Thirdly, at a situational level, the participants described both positive relationships, such as momentary friendships, and negative experiences of being excluded from the peer group. Pathways for further inquiries are discussed.

Nuclear factor erythroid-2 related factor 2 (Nrf2) is a transcription factor that regulates protection against a wide variety of toxic insults to cells, including cytotoxic cancer chemotherapeutic drugs. Many lung cancer cells harbor a mutation in either Nrf2 or its inhibitor Keap1 resulting in permanent activation of Nrf2 and chemoresistance. In this study, we sought to examine whether this attribute could be exploited in cancer suicide gene therapy by using a lentiviral (LV) vector expressing herpes simplex virus thymidine kinase (HSV-TK/GCV) under the regulation of antioxidant response element (ARE), a cis-acting enhancer sequence that binds Nrf2. In human lung adenocarcinoma cells in which Nrf2 is constitutively overexpressed, ARE activity was found to be high under basal conditions. In this setting, ARE-HSV-TK was more effective than a vector in which HSV-TK expression was driven by a constitutively active promoter. In a mouse xenograft model of lung cancer, suicide gene therapy with LV-ARE-TK/GCV was effective compared with LV-PGK-TK/GCV in reducing tumor size. We conclude that ARE-regulated HSV-TK/GCV therapy offers a promising approach for suicide cancer gene therapy in cells with high constitutive ARE activity, permitting a greater degree of therapeutic targeting to those cells. Cancer Res; 72(23); 6227–35. ©2012 AACR.

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PDF file - 324K, The effect of ganciclovir and doxorubicin on ARE activity

The effect of composition, size and number density of inclusions on the ductility of an experimental direct quenched ultra-high-strength low-alloy steel with a minimum specified tensile strength of 1300 MPa has been investigated. Two steels with impurity levels, i.e. total O+N+S contents, of 55 and 91 mass ppm have been studied. Both steels were Al-killed and Ca-treated, and had a martensitic microstructure after hot rolling and direct quenching. Ductility was characterized using tensile and Charpy V-notch testing. The number, size and composition of the inclusions were characterized using field emission scanning electron microscope with energy dispersive spectrometer (FESEM-EDS). At the higher impurity level of 91 ppm, the inclusion structure consisted of titanium nitrides, spherical calcium aluminates and elongated manganese sulphides, whereas at the lower impurity level of 55 ppm, the inclusion structure consisted of mainly fine spherical calcium aluminates with sulphide shells. The impurity level did not have a significant effect on the number density of inclusions, as with higher and lower impurity level the number of inclusions mm −2 was 80.5 and 73.8, respectively. However, the impurity level affected somewhat more the size distribution of the inclusions, as well as the composition of coarse inclusions with their longest length more than 8 µm. The number density of coarse inclusions mm −2 rose from 0.7 to 1.2 with increasing impurity level, and with the higher impurity level of 91 ppm, 72% of the coarse inclusions were titanium nitrides or manganese sulphides, whereas with the lower impurity level of 55 ppm, only 14% of the coarse inclusions were titanium nitrides while no manganese sulphides were detected. Coarse titanium nitrides were especially detrimental to the impact toughness. The number density of them should be below 0.4 mm −2 in order to guarantee the best possible toughness in the steel in question.

The effect of as-cast structure and macrosegregation on the mechanical properties of a direct-quenched low-alloy martensitic ultrahigh-strength aluminum killed and calcium treated steel cast at different superheats was studied. Samples from the castings were laboratory hot rolled with two different finishing rolling temperatures to distinguish the effect of hot rolling. Using optical emission spectrometry, the steel composition was analyzed as a function of slab thickness in order to detect the variations in steel chemistry due to macrosegregation. Further, hardness profiles, prior austenite grain sizes and tensile and impact toughness were determined for the hot-rolled specimens. It was found that interdendritic segregation was more intense at the higher superheat, which led to more pronounced positive segregation in the columnar-to-equiaxed transition (CET) zone, and negative segregation between CET and the centerline. These macrosegregation patterns were inherited by the hot-rolled samples causing local variations in hardness, which followed the variations in carbon content. However, altering the superheat had a minor effect on the nominal transformed microstructures and nominal prior austenite grain sizes. This occurred because of the interdendritic segregation induced composition variations both enlarged and decreased by turns the grain sizes. The CET also reduced measured impact toughness values.

A fair fraction of Pc1 pulsation events observed on the ground includes more than one simultaneous pulsation band. In most such multiband events the bands display different characteristics and, therefore, come from different source regions via horizontal ducting in the ionosphere. However, in this report we identify a new "coherent" subclass of multiband Pc1 events where the pearls of the simultaneous bands have the same group velocities (repetition rates) as well as dispersion and other properties, thus implying that the bands are produced by the same source. Studying one example of such a coherent multiband event in more detail, we argue that these events defy an explanation in terms of band splitting by magnetospheric heavy ions because the observed frequency gap between the bands is smaller than would result in such a case. We interpret these events to be due to the frequency dependence of the ionospheric reflection coefficient of Alfvén waves. An oscillatory frequency dependence of the coefficient is a natural consequence of the idea that the ionosphere acts as a resonator for Alfvén waves. We also discuss other predictions of this interpretation.

Results of the analysis of 15 unusual Pc1 pearl wave events with inverse dispersion in comparison with the dispersion of well-known electromagnetic ion-cyclotron (EMIC) waves in the form of classic pearl pulsations are presented. Pulsations with the dynamical spectrum consisting of both falling tones only (first type) and events with structures, which start with the falling tones and then develop into rising tones (second type), have been discovered. The first type corresponds to the frequency dispersion of magnetosonic waves (R-waves), and the second type corresponds to the mixed frequency dispersion of R-waves and EMIC waves (L-waves). All events were observed during quiet geomagnetic periods. The duration of the events is about 20-30 min. For the interpretation of these phenomena, the cyclotron instability driven by energetic proton beams with relative mean velocity v 0 directed along the background magnetic field and corresponding to an energy ∼10-100 keV is considered. The interaction of such proton beams with waves having frequencies ω T ∥ ) will be amplified. This instability is the reason for the generation of classic Pc1 pearl pulsations with the usual dispersion and allows explaining the transition of the dispersion from R- to L-waves.

We study structured and unstructured Pc1 pulsations observed at a high-latitude station (Sodankyla; L = 5.1) and a midlatitude station (Nurmijarvi; L = 3.3) during 18 storms occurring in low solar activity years (1976–1978 and 1984–1988). Pc1 activity was studied from the day of storm sudden commencement (denoted by day 0) onward during six consecutive days. While unstructured pulsations are only weakly affected, structured pulsations are greatly dependent on storm evolution. During the storm main phase they nearly vanish on the ground, despite strong wave activity in space. Structured Pc1 activity increases from day 0 to day 4 by a factor of about 4–5, reaching maximum occurrence on day 4 at both stations. Also, the average daily frequency of structured Pc1s increases from day 0 to a maximum on day 3 at Nurmijarvi or day 4 at Sodankyla. The diurnal distribution of structured Pc1s suffers a dramatic change during the storm. On days 1 and 2, structured pulsations are strongly concentrated in the evening sector, but during the later recovery (days 3–5) the activity shifts to the morning sector. The latitudinal similarity of structured Pc1 occurrence and the daily evolution of wave frequency argue against the model according to which the outward expansion of plasmapause causes the maximum wave occurrence on the ground on day 4. We also note that the strong maximum of structured Pels during the late storm recovery phase is not supported by the model calculations of the magnetospheric wave source or by direct observations of waves in space. Instead, we argue that the ionospheric resonator and propagation conditions which strongly affect wave observations on the ground are deteriorated during the storm main and early recovery phases, impeding wave propagation to the ground. The subsequent recovery of the ionospheric conditions leads to the maximum occurrence of structured Pc1s on the ground during the late storm recovery phase.

We study the properties of structured and unstructured Pc1 pulsations at a high-latitude station (Sodankyla; L =5.1) and a mid-latitude station (Nurmijarvi; L =3.3) during 18 storms occurring in low solar activity years. The storms were divided into two groups according to their intensity as measured by the minimum value of the D st index. Pc1 activity was studied from the day of the storm sudden commencement onwards during six consecutive days. Having recently published the average results for all 18 storms [Kerttula et al., J. Geophys. Res. (2000) in press], we concentrate here on the effect of magnetic storm intensity on wave properties. The source of structured Pc1s was found to be at lower latitudes during intense storms, in agreement with the lower latitude of the ring current during intense storms. Also, the source of unstructured Pc1s, the plasmasheet ions, was found to shift to lower latitudes during intense storms but this change was only observed in the early recovery phase. The great depletion of structured Pc1s on ground during the storm main and early recovery phase, which is in apparent disagreement with space observations and model calculations, is even more dramatic for intense storms. This further emphasizes the significance of the ionospheric conditions for wave observations on ground, and suggests that the depletion is due to deterioration of the ionospheric Alfven resonator during the storm main phase. Moreover, the results support the idea [Kerttula et al., J. Geophys. Res. 62 (2000) 299–309] that Pc1 occurrence maximum during late recovery phase is related to the improved ionospheric amplification and propagation conditions, rather than the outward expansion of the plasmapause.

A Pc1/IPDP event recorded by the Finnish search coil magnetometers on 15 December 1984 was analyzed in a companion paper (Mursula et al., 2000. Non-stationary Alfven resonator: new results on Pc1 pearls and IPDP events. J. Atmos. Solar-Terr. Phys. 62(4), 299–309) using numerical simulations of the ionospheric Alfven resonator (IAR). EISCAT incoherent scatter radar data were used to determine the vertical profiles of ionospheric plasma parameters. In this paper, the detailed altitude profiles of several wave characteristics at the IAR eigenfrequency are computed up to 1000 km height, including, e.g., the real normalized amplitude of the magnetic wave field component, ellipticity and orientation of the polarization ellipse in the horizontal plane. We also calculate the altitude profile of the energy flux density (Poynting vector). These features illustrate in detail the ionospheric effects on the wave spectral structure in a non-stationary IAR, and their significance in the formation of the Pc1/IPDP signal on the ground.

We analyse a Pc1 pearl event observed by the Finnish search-coil magnetometer network on 15 December 1984, which subsequently developed into a structured IPDP after a substorm onset. The EISCAT radar was simultaneously monitoring the mid- to high-latitude ionosphere. We have calculated the ionospheric resonator properties during the different phases of the event using EISCAT observations. Contrary to the earlier results, we find that the Pc1/IPDP (Interval of Pulsations of Diminishing Period) frequency observed on the ground corresponds to the maximum of the transmission coefficient rather than that of the reflection coefficient. This casts strong doubts on the bouncing wave packet model of Pc1 pearls. Instead, we present evidence for an alternative model of pearl formation in which long-period ULF waves modulate the Pc1 growth rate. Moreover, we propose a new model for IPDP formation, whereby the ionosphere acts as an active agent in forming the IPDP signal on the ground. The model calculations show that the ionospheric resonator properties can be modified during the event so that the resonator eigenfrequency increases according to the observed frequency increase during the IPDP phase. We suggest that the IPDP signal on the ground is a combined effect of the frequency increase in the magnetospheric wave source and the simultaneous increase of the resonator eigenfrequency. The need for such a complicated matching of the two factors explains the rarity of IPDPs on the ground despite the ubiquitous occurrence of EMIC waves in the magnetosphere and the continuous substorm cycle.

In this paper we study structured Pc1 pulsations (also called Pc1 pearls) observed on ground, concentrating on the relation between the pearl repetition period τ and the wave frequency f. Earlier studies suggest that the product τ f is roughly constant. We reexamine this relation and show that a simple inverse law is excluded. Instead, our observations suggest the relation τ ∝ f−p, with p = 0.59 ± 0.06, posing a new, strict constraint on theories of Pc1 pearl formation. We also study the L dependence of various combinations of τ and f using a model L value and extract additional constraints from these combinations. We discuss these constraints in the bouncing wave packet model of pearl formation and determine the range of allowed parameter values in this model. We present two models of energetic ions with different L distributions and show that one of them can be excluded by the constraints derived. We also discuss how to further improve on these constraints to better test the bouncing wave packet model and other theories of Pc1 pearl formation.

The JYFLTRAP double Penning-trap system was moved to a new location along with the Ion Guide Isotope Separator On-line (IGISOL) facility at the Accelerator Laboratory of the University of Jyvaskyla. The move made it possible to upgrade various parts of the facility. For example, separate beam lines for JYFLTRAP and the collinear laser spectroscopy station were constructed after the radio-frequency quadrupole cooler and buncher. In this contribution we give an overview of the new JYFLTRAP facility and results from the first stable ion-beam tests.

We discuss the ponderormotive redistribution of ions along geomagnetic field lines due to the action of Pc 1 pulsations, using a simple diffusion equilibrium model. The field-aligned component of the ponderomotive force is derived for Alfven waves as well as for ion cyclotron waves propagating in a multicomponent plasma. Our theory gives a possibility for a better understanding of the problem and a convenient way to make rough estimates of the ponderomotive efficiency of Pc 1 waves under concrete magnetospheric conditions. Qualitative analysis of equations and satellite information on the intensity of wave fields show that the ponderomotive forces can have a pronounced effect on plasma. Ground-based observations of Pc 1 pulsations also suggest a ponderomotive redistribution of the background plasma.

In this paper we investigate fluctuations of the repetition period of geomagnetic Pc1 pearl pulsations. Starting from calculated repetition period we present a general formula for the deviation of the repetition period as a function of wave frequency and stochastic parameters of the medium along the ray trace. We then apply this formula for a dipole magnetic field with a simple plasma distribution, and show that a linear correlation between repetition period and its deviation is predicted. This correlation and the frequency dependence of fluctuations are then compared with experimental values measured from selected Pc1 pearl events observed in Finland.

Ion cyclotron wave (Pc1 pulsation) activity on the ground has been found to depend strongly on solar activity: Pc1 pulsations occur considerably more often during solar minimum than solar maximum conditions. We have now studied Pc1 wave activity observed by the AMPTE/CCE satellite close to the equatorial source region of these waves, and simultaneously on the ground at Sodankyla, Finland, during two periods of contrasting solar activity levels: August 1985 – May 1986 (with average daily sunspot number of 13.9) and May 1988 – January 1989 (118.2). The total occurrence rate of waves in space decreased by a factor 1.6 from low to high sunspot times, in good agreement with a simultaneous decrease observed for high-latitude unstructured Pc1's on ground. The structured Pc1's (classical pearls) suffer a greater depletion in high sunspot times. The data suggests that the long-term variation of high-latitude Pc1's may entirely be due to a change in wave generation. Another, holistic view on wave appearance in a given flux tube with several factors affecting the observed changes is also possible. Ionospheric ducting does not seem to be a significant factor in regulating long-term activity of high-latitude Pc1's. The data also suggests a nonlinear dependence between Pc1 activity and solar activity as measured by sunspot mumbers.

The authors study the existence of stop bands for left-handed Alfvenic ion cyclotron waves propagating in the direction of magnetic field in a multicomponent plasma. Three effects are discussed: finite ion temperature, inhomogeneous magnetic field, and nonlinear wave amplitude. All of them affect the existence of stop bands and set critical bounds on the relevant physical parameters, particularly on the density of heavy ions. Using the model of a linearly varying, longitudinally inhomogeneous magnetic field, they calculate the critical lower bound on heavy ion density as a function of longitudinal inhomogeneity, and they discuss the difference between the truly inhomogeneous and essentially homogeneous situations. Typical values for the wave vector in the resonance region are derived. They also find the upper bound on the wave amplitude for the linear theory to be applicable, and the authors derive the condition for stop band formation in the nonlinear case. The obtained results are applied to the magnetospheric environment and are shown to lead to relevant modifications. For example, the formation of stop bands by thermal heavy ions is strongly dependent on the local inhomogeneity of the magnetic field.

The effect of superheat on grain sedimentation and macrosegregation has been investigated using experimental castings of a low-alloyed steel grade. With a high superheat of ~ 40 °C, the central equiaxed parts of the slabs consisted of randomly oriented fine dendrites but with a low superheat of ~ 10 °C, coarse globular structures formed. The mean carbon content measured with optical emission spectroscopy was of the order of 15% smaller with coarse globular structures than in fine equiaxed dendritic structures. Electron probe microanalysis of other alloying elements indicates that the negative segregation in the slab central zones is caused by sedimentation of globulites. With superheat in the range ~ 20 - 40 °C, the equiaxed zone is bordered by a columnar to equiaxed transition (CET) zone. In this region a positive macrosegregation of carbon and other alloying elements was observed. These phenomena are important when considering the through-thickness properties of the slabs and final products.

Although focal adhesion kinase (FAK) is elevated in epithelial cancers, it is not known whether FAK expression influences tumor development in vivo. We found that fak +/- heterozygous mice display reduced 7,12-dimethylbenz[a]anthracene-induced papilloma formation that correlates with reduced FAK protein expression in the skin. However, the frequency of malignant conversion of papillomas into carcinomas is indistinguishable in fak +/- mice and their wild-type fak +/+ littermates, most likely because papilloma FAK protein expression is elevated to wild-type levels. We also found that keratinocyte FAK protein expression is important for cellular responses downstream of ras in vitro (monitored by extracellular signal-regulated kinase activation after integrin engagement). Because 7,12-dimethylbenz[a]anthracene induces an activating mutation of H-ras, this provides one possible explanation for suppression of papilloma formation when FAK protein is limiting.

An old but rarely used resonance method is introduced and examined in order to study the very long term occurrence of Pc 1 micropulsations. By this method it is possible to detect Pc 1 pulsations with a frequency close to the eigenfrequency of the magnetometer system. We have analyzed the magnetograms of the LaCour-type magnetometer used in a quick-run operation at the high-latitude station of Sodankyla, Finland. The eigenfrequencies of the three components covered the frequency range from about 0.3 to 0.5 Hz. Our analysis extends over the whole registration period from 1932 to 1944 and from 1953 to 1983, i.e., covering nearly four solar cycles. The results show a very strong negative correlation between the annual Pc 1 activity and the annual sunspot number which persists over the whole data period. According to the statistics obtained, it is, for example, very unlikely that the Pc 1 activity maximum at a high-latitude station would occur during the declining phase of the sunspot cycle. Furthermore, as a result of the negative correlation, some of the differences between the various solar cycles can be seen in the corresponding cycles of annual Pc 1 activity. Our results also reveal some new features common for the long-term variations of Pc 1 activity at high- and mid-latitude stations and help in understanding the differences between them.

Electric field has been measured by the EISCAT incoherent scatter radar during an IPDP (Intervals of Pulsations of Diminishing Periods) type plasma wave event. The event was recorded in the local late evening-midnight sector. The electric field has a significant westward component during the IPDP. We demonstrate that the radial inward drift of the magnetospheric plasma under the observed electric field can explain the increasing frequency in this IPDP.

We report the isolation and characterization of six overlapping cDNA clones that provide the first and complete amino acid sequence of the human laminin B1 chain. The cDNA clones cover 5613 nucleotides with 5358 nucleotides in an open reading frame encoding 1786 amino acids, including a 21-residue signal peptide-like sequence. Sequence analysis demonstrated the presence of two types of internal homology repeats that were found in clusters within the polypeptide chain. The type A repeats contain about 50 amino acids of which 8 are cysteine. These repeats are present in two clusters toward the NH2-terminal end of the chain and are separated from each other by about 220 amino acids. The two clusters contain five and eight consecutive repeats each. There are two copies of consecutive type B repeats of about 40 amino acids close to the COOH-terminal end. Computer analysis of the amino acid sequence of the B1 chain revealed the presence of structurally distinct domains that contain cysteine-rich repeats, globular regions, and helical structures. Using somatic cell hybrid methodology and in situ hybridization to metaphase chromosomes it was established that the human laminin B1 gene (LAMB1) is located in the q22 region of chromosome 7.

The source of Pc 1 (pearl) pulsations observed in the course of the local morning hours on 7 December 1977 has been determined by the amplitude and group delay methods. The frequency of pulsations exhibit the typical diurnal variation with the maximum frequency during dawn hours. The source location of pearls during every 1-h interval is compared with the position of the plasmapause inferred from the GEOS I measurements and from previous statistical analysis. It is shown that the source of high-frequency pulsations (f > 1 Hz) is well inside the plasmapause whereas low-frequency pulsations (f < 1 Hz) occur near the plasmapause. The source of pulsations is displaced to higher L-values in the course of the local morning hours and this displacement is associated with the decrease of the frequency of pulsations. The source displacement is much more pronounced than the simultaneous movement of the plasmapause position. These observations imply that the model of the Pc1 generation which locates the source only at the plasmapause has serious shortcomings. A model is discussed which takes into account the generation of Pc1 pulsations also well inside the plasmapause and the properties of the waveguide propagation of waves in the ionspheric duct.

We show two examples of magnetic pulsation recordings which illustrate that IPDP type wave events can occur simultaneously in the evening and morning sectors of the magnetosphere. This is a further confirmation that the generation of morning IPDP's is also associated with the enhancement of magnetospheric electric fields and energetic plasma during substorms.

We analyse data from the Finnish north-south chain of riometers and pulsation magnetometers to show that there is a type of electron precipitation event in the aftemoon-to-evening sector of the auroral and sub-auroral zone which occurs simultaneously with IPDP pulsation events. These events show concurrent motions of their sources. We conclude that in these cases riometer absorption events can be used to trace the movements of the source field line of pulsations. This information is used in model calculations which simulate the motions of the IPDP source region by taking into account the geometry of the particle injection boundary in the midnight sector and the westward drift of energetic protons in the magnetosphere.

Mercury's surface brightness has been measured from 16 photographic plates representing an equal amount of different phases. The resulting photometric function turns out to be almost identical with the lunar photometric function.

Laminin B2 is one of the three polypeptide chains of laminin. a large, complex glycoprotein synthesized by a variety of cells and specifically deposited in basement membranes. A cloned cDNA that encodes the human laminin B2 chain was isolated and characterized. The human laminin B2 gene (LAMB2) was assigned to region 1q25→q31 by (1) hybridization of the probe to DNA from a panel of human × mouse somatic cell hybrids containing different human chromosomes and (2) in situ hybridization to isolated metaphase chromosomes.

We report the isolation and characterization of six overlapping cDNA clones that provide the first and complete amino acid sequence of the human laminin B1 chain. The cDNA clones cover 5613 nucleotides with 5358 nucleotides in an open reading frame encoding 1786 amino acids, including a 21-residue signal peptide-like sequence. Sequence analysis demonstrated the presence of two types of internal homology repeats that were found in clusters within the polypeptide chain. The type A repeats contain about 50 amino acids of which 8 are cysteine. These repeats are present in two clusters toward the NH2-terminal end of the chain and are separated from each other by about 220 amino acids. The two clusters contain five and eight consecutive repeats each. There are two copies of consecutive type B repeats of about 40 amino acids close to the COOH-terminal end. Computer analysis of the amino acid sequence of the B1 chain revealed the presence of structurally distinct domains that contain cysteine-rich repeats, globular regions, and helical structures. Using somatic cell hybrid methodology and in situ hybridization to metaphase chromosomes it was established that the human laminin B1 gene (LAMB1) is located in the q22 region of chromosome 7.

Intervals of pulsations of dimminishing periods (IPDP) magnetic pulsation data have been analyzed from several recording compaigns and from stations that are widely spaced in both meridional and azimuthal directions. On the basis of their local time occurrence it seems useful to divide the events into at least two main categories: 1400

We report that intervals of pulsations of diminishing periods (IPDP) type plasma events which are associated with magnetospheric substorms are less frequent in the years of high solar acitivity than in years of low activity. This new result is based on two independent continuous data sets from 1974 to 1985. We show also that IPDP events occur throughout the recurrent magnetic storms in 1976, whereas they appear more sporadically in 1980, i.e., during high solar activity. It is concluded that several factors such as changes in plasmapause position, attenuation of horizontal ionospheric wave propagation, and heavy ion densities in the magnetosphere can contribute to the observed long-term variability. copyright American Geophysical Union 1988