Solar maximum epoch imprints in tree-ring width from Passo Fundo,Brazil (1741–2004)

A tree-ring thickness time series from Passo Fundo (Southern Brazil) for the interval 1741–2004 was studied by spectral, wavelet and cross-wavelet analyses in order to identify the non-stationary characteristics in tree-ring and sunspot number data. Periods corresponding to the solar cycles of 11, 22, and 80 yr were found. The 11 yr solar cycle is detected in tree-ring data only during maximum solar activity interval from 1764 to 1804, 1824 to 1884, and 1924 to 1984. The Hale 22 yr solar cycle was observed in tree-ring wavelet map for the 1764–1864 and 1904–2004 intervals. The Gleissberg solar cycle was also observed in tree-ring wavelet map for the 1844–1904 interval.     

Solar activity imprints in tree ring width from Chile (1610–1991)

We have investigated the solar activity signal in tree ring data from two locations in Chile. The tree ring time series extended over a period of ∼400 yr. Spectral and wavelet analysis techniques were employed. We have found evidence for the presence of the solar activity Schwabe (∼11 yr), Hale (∼22 yr), fourth-harmonic of the 208-yr Suess cycle (∼52 yr) and Gleissberg (∼80 yr) cycles. The Gleissberg cycle of tree ring data is in anti-phase with solar activity. Wavelet and cross-wavelet techniques revealed that the periods found are intermittent, possibly because solar activity signals observed in tree rings are mostly due to solar influence on local climate (rainfall, temperature, and cloud cover) where trees grow up. Further, cross-wavelet analysis between sunspot and tree ring time series showed that the cross power around the 11 yr solar cycle is more significant during periods of high solar activity (grand maximum) than during periods of low solar activity (grand minimum). As Glaciar Pio XI is practically at the Pacific Ocean level, the tree-ring response may be stronger due to the heating of the Pacific Ocean water following an increase of the solar radiation incidence rather than at the higher altitudes of Osorno region.     

Descriptive study of solar activity sudden increase and Halloween storms of 2003

During the declining phase of the last three solar cycles, secondary peaks have been detected 2–3 years after the main peak of sunspot number. The main peak of cycle 23 was in 2001, but a sudden increase of the solar activity occurred during the period October 17 to November 10, 2003 (the so-called Halloween storms). A similar storm occurred 1 year later, during the period October 3 to November 13, 2004. These events are considered as secondary peaks during the declining phase of cycle 23. Secondary peaks during declining phase of the last 10 solar cycles were detected by Gonzalez and Tsurutani [1990. Planetary and Space Science 38, 181–187]. During Halloween storm period, the sunspot area increased up to 1.11×10^?9 hemisphere on October 19, and grow up to 5.69×10^?9 hemisphere on October 30, 2003. Then it decreased to 1.11×10^?9 hemisphere on November 4, 2003. Also, the radio flux of λ=10.7 cm increased from 120 sfu on October 19, to 298 sfu on October 26, 2003, then decreased to 168 sfu on November 4, 2003. Two eruptive solar proton flares were released on 26 and 28 October 2003, the latter being the most eruptive flare recorded since 1976 (values reaching X17/4B).The aim of this study is to follow the morphological and magnetic changes of the active region before, during, and after the production of high-energy flares. Furthermore, the causes of release of these eruptive storms have been discussed for the period, October–November 2003, during the declining phase of the solar cycle 23.     

Modelling the Northern Hemisphere temperature for solar cycles 24 and 25

It is uncertain whether the solar cycle 24 will have a high or a low sunspot maximum number. In its last revision the Solar Cycle 24 Prediction Panel indicates that the low prediction is the most likely. Also, solar cycle 25 is considered to present an equal or lower activity than cycle 24. In order to assess the possible effect of the solar activity on temperature, in the present work we attempt to model the tendency of the Northern Hemisphere temperature for the years 2009–2029, corresponding to solar cycles 24 and 25, using a thermodynamic climate model. We include as forcings the atmospheric carbon dioxide (CO₂) and the solar activity by means of the total solar irradiance, considering that the latter has not only a direct effect on climate, but also an indirect one through the modulation of the low cloud cover. We use two IPCC-2007 CO₂ scenarios, one with a high fossil consumption and other with a low use of fossil sources. Also we consider higher and lower solar activity conditions. We found that in all the performed experiments the inclusion of the solar activity produces a noticeable reduction in warming respect to the IPCC-2007 CO₂ scenarios. Such reduction goes between ～14% and ～44%. In order to evaluate the efficiency of the TCM, we use the root mean square (RMS) between the observed and model temperatures for the period 1980–2003. We find that the RMS for the experiment using the CO₂ as the only forcing is 0.06 °C,while for the experiment that includes also the solar activity it is higher, 0.13 °C.     

Phase-coherent oscillatory modes in solar and geomagnetic activity and climate variability

Oscillatory modes with the period of approximately 7–8 yr were detected in monthly time series of sunspot numbers, geomagnetic activity aa index, NAO (North Atlantic Oscillation) index and near-surface air temperature from several mid-latitude European locations. Instantaneous phases of the modes underwent synchronization analysis and their statistically significant phase coherence, beginning from 1950s, has been observed. Thus the statistical evidence for a coupling between solar/geomagnetic activity and climate variability has been obtained from continuous monthly data, independent of the season, however, confined to the temporal scale related to oscillatory periods about 7–8 yr.     

Solar dynamo and geomagnetic activity

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 20 m/s (averaged over latitude and over the sunspot cycle), the deep circulation varied between 2.5 and 5.5 m/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.     

A 22 yr hurricane cycle and its relation with geomagnetic activity

Applying spectral analysis to the Atlantic and Pacific hurricane time series, we found periodicities that coincide with the main sunspot and magnetic solar cycles. To assess the possibility that these periodicities could be associated with solar activity, we obtain correlations between hurricane occurrence and several solar activity-related phenomena, such as the total solar irradiance, the cosmic ray flux and the Dst index of geomagnetic activity. Our results indicate that the highest significant correlations are found between the Atlantic and Pacific hurricanes and the Dst index. Most importantly, both oceans present the highest hurricane–Dst correlations during the ascending part of odd solar cycles and the descending phase of even solar cycles. This shows not only the existence of a 22 yr cycle but also the nature of such periodicity. Furthermore, we found that the Atlantic hurricanes behave differently from the Pacific hurricanes in relation to the solar activity-related disturbances considered.     

Interplanetary origins of November 2004 superstorms

The sun was very active in the declining phase of solar cycle 23. Large sunspot active regions gave origin to multiple flare and coronal mass ejection (CME) activity in the interval 2003–2005. On November 2004, the active region AR 10696 was the origin of dozens of flares and many CMEs. Some events of this solar activity region resulted in two large geomagnetic storms, or superstorms (Dst??250 nT) on November 8, peak Dst=?373 nT, and on November 10, peak Dst=?289 nT. It is the purpose of this article to identify the interplanetary origins of these two superstorms. The southward-directed interplanetary magnetic fields (IMF Bs) that caused the two superstorms were related to a magnetic cloud (MC) field for the first superstorm, and a combination of sheath and MC fields for the second superstorm. However, this simple, classic picture is complicated by the presence of multiple shocks and waves. Six fast-forward shocks and, at least, two reverse waves were observed in the period of the two superstorms. A detailed analysis of these complex interplanetary features is performed in this work.     

Astrochronology of the late Jurassic Kimmeridge Clay (Dorset,England) and implications for Earth system processes

The Late Jurassic Kimmeridge Clay Formation (KCF) is an economically important, organic-rich source rock of Kimmeridgian–Early Tithonian age. The main rock types of the KCF in Dorset, UK, include grey to black laminated shale, marl, coccolithic limestone, and dolostone, which occur with an obvious cyclicity at astronomical timescales. In this study, we examine two high-resolution borehole records (Swanworth Quarry 1 and Metherhills 1) obtained as part of a Rapid Global Geological Events (RGGE) sediment drilling project. Datasets examined were total organic carbon (TOC), and borehole wall microconductivity by Formation Microscanner (FMS). Our intent is to assess the rhythmicity of the KCF with respect to the astronomical timescale, and to discuss the results with respect to other key Late Jurassic geological processes. Power spectra of the untuned data reveal a hierarchy of cycles throughout the KCF with ～ 167 m, ～ 40 m, 9.1 m, 3.8 m and 1.6 m wavelengths. Tuning the ～ 40 m cycles to the 405-kyr eccentricity cycle shows the presence of all the astronomical parameters: eccentricity, obliquity, and precession index. In particular, ～ 100-kyr and 405-kyr eccentricity cycles are strongly expressed in both records. The 405-kyr eccentricity cycle corresponds to relative sea-level changes inferred from sequence stratigraphy. Intervals with elevated TOC are associated with strong obliquity forcing. The 405-kyr-tuned duration of the lower KCF (Kimmeridgian Stage) is 3.47 Myr, and the upper KCF (early part of the Tithonian Stage, elegans to fittoni ammonite zones) is 3.32 Myr. Two other chronologies test the consistency of this age model by tuning ～ 8–10 m cycles to 100-kyr (short eccentricity), and ～ 3–5 m cycles to 36-kyr (Jurassic obliquity). The ‘obliquity-tuned’ chronology resolves an accumulation history for the KCF with a variation that strongly resembles that of Earth's orbital eccentricity predicted for 147.2 Ma to 153.8 Ma. There is evidence for significant non-deposition (up to 1 million years) in the lowermost KCF (baylei–mutabilis zones), which would indicate a Kimmeridgian/Oxfordian boundary age of 154.8 Ma. This absolute calibration allows assignment of precise numerical ages to zonal boundaries, sequence surfaces, and polarity chrons of the lower M-sequence.     

The variation of ionospheric slab thickness over equatorial ionization area crest region

The GPS-derived total electron content (TEC) and NmF2 are measured at the Chung-Li ionosonde station (24.9°N, 121°E) in order to study the variations in slab thickness (τ) of the ionosphere at low-latitudes ionosphere during 1996–1999, corresponding to half of the 23rd solar cycle. This study presents the diurnal, seasonal, and solar flux variations in τ for different solar phases. The seasonal variations show that the average daily value is greater during summer and the reverse is true during equinox in the equatorial ionization anomaly (EIA) region. Moreover, the τ values are greater during the daytime (0800–1600 LT) and nighttime (2000–0400 LT) for summer and winter, respectively. The diurnal variation shows two abnormal peaks that appear during the pre-sunrise and post-sunset hours. The peak values decrease as the sunspot number increases particularly for the pre-sunrise peak. Furthermore, the variation in the F-peak height (hpF2) indicates that a thermospheric wind toward the equator leads to an increase in hpF2 and an enhancement in τ during the pre-sunrise period. Furthermore, the study shows the variations of τ values for different geophysical conditions such as the geomagnetic storm and earthquake. A comprehensive discussion about the relation between τ and the geophysical events is provided in the paper.     

Are there connections between the Earth's magnetic field and climate?

Understanding climate change is an active topic of research. Much of the observed increase in global surface temperature over the past 150 years occurred prior to the 1940s and after the 1980s. The main causes invoked are solar variability, changes in atmospheric greenhouse gas content or sulfur due to natural or anthropogenic action, or internal variability of the coupled ocean–atmosphere system. Magnetism has seldom been invoked, and evidence for connections between climate and magnetic field variations have received little attention. We review evidence for correlations which could suggest such (causal or non-causal) connections at various time scales (recent secular variation ∼ 10–100 yr, historical and archeomagnetic change ∼ 100–5000 yr, and excursions and reversals ∼ 10³–10⁶ yr), and attempt to suggest mechanisms. Evidence for correlations, which invoke Milankovic forcing in the core, either directly or through changes in ice distribution and moments of inertia of the Earth, is still tenuous. Correlation between decadal changes in amplitude of geomagnetic variations of external origin, solar irradiance and global temperature is stronger. It suggests that solar irradiance could have been a major forcing function of climate until the mid-1980s, when “anomalous” warming becomes apparent. The most intriguing feature may be the recently proposed archeomagnetic jerks, i.e. fairly abrupt (∼ 100 yr long) geomagnetic field variations found at irregular intervals over the past few millennia, using the archeological record from Europe to the Middle East. These seem to correlate with significant climatic events in the eastern North Atlantic region. A proposed mechanism involves variations in the geometry of the geomagnetic field (f.i. tilt of the dipole to lower latitudes), resulting in enhanced cosmic-ray induced nucleation of clouds. No forcing factor, be it changes in CO₂ concentration in the atmosphere or changes in cosmic ray flux modulated by solar activity and geomagnetism, or possibly other factors, can at present be neglected or shown to be the overwhelming single driver of climate change in past centuries. Intensive data acquisition is required to further probe indications that the Earth's and Sun's magnetic fields may have significant bearing on climate change at certain time scales.     

Modeled tephra ages from lake sediments,base of Redoubt Volcano,Alaska

A 5.6-m-long lake sediment core from Bear Lake, Alaska, located 22 km southeast of Redoubt Volcano, contains 67 tephra layers deposited over the last 8750 cal yr, comprising 15% of the total thickness of recovered sediment. Using 12 AMS ¹⁴C ages, along with the ¹³⁷Cs and ²¹⁰Pb activities of recent sediment, we evaluated different models to determine the age–depth relation of the core, and to determine the age of each tephra deposit. The selected age model is based on a mixed-effect regression that was passed through the adjusted tephra-free depth of each dated layer. The estimated age uncertainty of the 67 tephras averages ±105 yr (95% confidence intervals). Tephra-fall frequency at Bear Lake was among the highest during the past 500 yr, with eight tephras deposited compared to an average of 3.7/500 yr over the last 8500 yr. Other periods of increased tephra fall occurred 2500–3500, 4500–5000, and 7000–7500 cal yr. Our record suggests that Bear Lake experienced extended periods (1000–2000 yr) of increased tephra fall separated by shorter periods (500–1000 yr) of apparent quiescence. The Bear Lake sediment core affords the most comprehensive tephrochronology from the base of the Redoubt Volcano to date, with an average tephra-fall frequency of one every 130 yr.     

GPS constraints on the deformation of Azerbaijan and surrounding regions

In this study, we present new GPS observations in Azerbaijan to provide an improved basis for determining the distribution of crustal deformation throughout the country and surrounding areas. The deformation field in the region has been analyzed with a dense GPS network configuration and a reliable quantification of the ongoing deformation was achieved. Results show that while contraction is dominant over the whole region, it is mostly concentrated on the middle and eastern parts of Caucasus Thrust Fault reaching up to 6.4 ± 0.2 mm/yr and Lesser Caucasus Fault does no accommodate more than 1–2 mm/yr of contraction. New network also clearly substantiates that the West Caspian Fault, which is a continuation of Caucasus Thrust Fault in the south, accommodates right-lateral slip rates of 7.1 ± 0.3 mm/yr in addition to 5.5 ± 0.3 mm/yr contraction rates.     

Changed relation between sunspot numbers,solar UV/EUV radiation and TSI during the declining phase of solar cycle 23

We study the mutual relation of sunspot numbers and several proxies of solar UV/EUV radiation, such as the F10.7 radio flux, the HeI 1083 nm equivalent width and the solar MgII core-to-wing ratio. It has been noted earlier that the relation between these solar activity parameters changed in 2001/2002, during a large enhancement of solar activity in the early declining phase of solar cycle 23. This enhancement (the secondary peak after the Gnevyshev gap) forms the maximum of solar UV/EUV parameters during solar cycle 23. We note that the changed mutual relation between sunspot numbers and UV/EUV proxies continues systematically during the whole declining phase of solar cycle 23, with the UV/EUV proxies attaining relatively larger values for the same sunspot number than during the several decennia prior to this time. We have also verified this evolution using the indirect solar UV/EUV proxy given by a globally averaged f₀(F2) frequency of the ionospheric F2 layer. We also note of a simultaneous, systematic change in the relation between the sunspot numbers and the total solar irradiance, which follow an exceptionally steep relation leading to a new minimum. Our results suggest that the reduction of sunspot magnetic fields (probably photospheric fields in general), started quite abruptly in 2001/2002. While these changes do not similarly affect the chromospheric UV/EUV emissions, the TSI suffers an even more dramatic reduction, which cannot be understood in terms of the photospheric field reduction only. However, the changes in TSI are seen to be simultaneous to those in sunspots, so most likely being due to the same ultimate cause.     

Ground-based Pc5 ULF wave power: Solar wind speed and MLT dependence

Using over 20 years of ground-based magnetometer data from the CANOPUS/CARISMA magnetometer array, we present a statistical characterisation of Pc5 ultra-low frequency (ULF) power in the 2–10 mHz band as a function of magnetic local time (MLT), L-shell, and solar wind speed. We examine the power across L-shells between 4.2 and 7.9, using data from the PINA, ISLL, GILL and FCHU stations, and demonstrate that there is a significant MLT dependence in both the H- and D-component median 2–10 mHz power during both fast (>500 km/s) and slow (<500 km/s) solar wind speeds. The H-component power consistently dominates over D-component power at all MLTs and during both fast and slow solar wind. At the higher-L stations (L>5.4), there are strong MLT power peaks in the morning and midnight local time sectors; the morning sector dominating midnight during fast solar wind events. At lower L-shells, there is no evidence of the midnight peak and the 2–10 mHz power is more symmetric with respect to MLT except during the fastest solar wind speeds. There is little evidence in the ground-based power of a localised MLT peak in ULF power at dusk, except at the lowest L-shell station, predominantly in the H-component. The median 2–10 mHz power increases with an approximate power law dependence on solar wind speed, at all local times across the L-shell domain studied in both components. The H-component power peaks at the latitude of the GILL station, with significantly lower power at both higher and lower L-shells. Conversely, the D-component power increases monotonically. We believe that this is evidence for 2–10 mHz power accumulating at auroral latitudes in field line resonances. Finally, we discuss how such ULF wave power characterisation might be used to derive empirical radiation belt radial diffusion coefficients based on, and driven by, the solar wind speed dependence of ULF wave power.     

Geochemistry,chronology and stratigraphy of Neogene tuffs of the Central Andean region

Tuff layers are vital stratigraphic tools that allow correlations to be made between widely dispersed exposures. Despite their widespread occurrence in the central Andes, tuffs from both natural exposures and sedimentary cores extracted from the region's extensive salars (salt pans) are relatively unstudied. Here we lay the foundation for a tephrostratigraphic framework in the central Andes (14–28°S) by chemically and morphologically characterizing ash shards, and in some cases dating 36 Neogene distal tuffs. These tuffs occur in lacustrine and alluvial deposits from the southern Bolivian Altiplano and adjacent Atacama Desert. All tuffs are calc-akaline rhyolites, consistent with their setting in the Central Andean Volcanic Zone. Five of the older tuffs were ⁴⁰Ar/³⁹Ar dated and yield an age range of 6.63–0.75 Ma. Organic material associated with tuffs deposited into paleolake sediments, paleowetland deposits, or urine-encrusted rodent middens provide constraints on the age of several Late Pleistocene and Holocene tuffs.These tuffs provide key stratigraphic markers and ages for lake cycles and archeological sites on the Bolivian Altiplano and for assessing rates of surficial processes and archeology in both the Atacama and Altiplano. While modern climate, and consequently questions about geomorphic processes and climate change, differs in the hyperarid Atacama and the semi-arid Altiplano, the most extensive air-fall tuffs covered both regions, placing the Atacama and the Bolivian Altiplano in the same tephrostratigraphic province. For example, the Escara B tuff (～1.85 Ma), can be securely identified in both the Altiplano and Atacama. On the Altiplano, dates from the Escara B and E tuffs securely establish the age of the Escara Formation—representing the oldest expansive lake documented on the Bolivian Altiplano. By contrast, the presence of the Escara B tuff below ～6 m of alluvial sediment at the Blanco Encalado site in the Atacama desert yields information about sedimentation rates in this hyperarid region. Indeed, most tuffs from the Atacama Desert are older than 600,000 years, even though they occur within fluvial terraces immediately adjacent to the alluvial fans that are still active. Most of these geomorphic surfaces in the Atacama also possess well-developed saline soils that, when combined with the radiometric ages of the distal tuffs, suggest slow rates of geomorphic change and exceptional landscape stability for this area during the Quaternary.In contrast, younger tuffs are more abundant in the more recent lake records of the Altiplano. The Chita tuff was deposited at ～15,650 cal yr B.P., during the regressive phase of the region's deepest late Quaternary lake cycle—the “Tauca lake cycle”—which spanned 18.1–14.1 cal yr B.P. Two Holocene tuffs, the Sajsi tuff and the Cruzani Cocha tuff, are widespread. The Sajsi tuff was deposited just before 1700 cal yr B.P., whereas the Cruzani Cocha tuff appears to be mid-Holocene in age and shows some chemical affinities to a Holocene tuff (202B) deposited between 4420 and 5460 cal yr B.P. in a urine-encased rodent midden in the Atacama Desert.     

Primitive neon and helium isotopic compositions of high-MgO basalts from the Kerguelen Archipelago,Indian Ocean

The geochemical characteristics of mildly alkalic basalts (24–25 Ma) erupted in the southeastern Kerguelen Archipelago are considered to represent the best estimate for the composition of the enriched Kerguelen plume end-member. A recent study of picrites and high-MgO basalts from this part of the archipelago highlighted the Pb and Hf isotopic variations and suggested the presence of mantle heterogeneities within the Kerguelen plume itself. We present new helium and neon isotopic compositions for olivines from these picrites and high-MgO basalts (6–17 wt.% MgO) both to constrain the enriched composition of the Kerguelen plume and to determine the origin of isotopic heterogeneities involved in the genesis of Kerguelen plume-related basalts. The olivine phenocrysts have extremely variable ⁴He / ³He compositions between MORB and primitive values observed in OIB (∼90,000 to 40,000; i.e., R / R_a ∼8 to 18) and they show primitive neon isotopic ratios (average ²¹Ne / ²¹Ne_ext ∼0.044). The neon isotopic systematics and the ⁴He / ³He ratios that are lower than MORB values for the Kerguelen basalts clearly suggest that the Kerguelen hotspot belongs to the family of primitive hotspots, such as Iceland and Hawaii. The rare gas signature for the Kerguelen samples, intermediate between MORB and solar, is apparently inconsistent with mixing of a primitive component with a MORB-like source, but may result from sampling a heterogeneous part of the mantle with solar ³He / ²²Ne and with a higher (U, Th) / ³He ratio compared to typically high R / R_a hotspot basalts such as those from Iceland and Hawaii.     

Validation of temperature measurements from MIPAS-ENVISAT with balloon observations obtained by MIPAS-B

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), a limb sounding Fourier transform interferometer in the mid-infrared band, on board the polar-orbiting ENVIronmental SATellite (ENVISAT) was launched in March 2002 by the European Space Agency (ESA). For the MIPAS data validation, three balloon flights with MIPAS-B, a balloon version of MIPAS, were carried out on the 24th and 25th of September 2002 from Aire sur l’Adour (France 44°N, 0°E), on the 20th and 21th of March, and on the 2nd and 3rd of July 2003 from Esrange, Kiruna (Sweden 68°N, 21°E). The MIPAS operational data version 4.61 for the temperature vertical profiles were compared with the correlative MIPAS-B measurements via the coincident comparison and the trajectory comparison approaches, respectively. The precision of the MIPAS temperature was estimated to be 1.04–2.48 K in the region 123–8 hPa (15–33 km) and beyond the expectation. The systematic difference shows that the absolute accuracy of the MIPAS temperature is within the total combined errors between 356 and 3 hPa (8–39 km). The agreements in the middle stratosphere are better than in the lower stratosphere and upper troposphere. The maximum difference of 1.9 K (0.9%) was found at 228 hPa (11 km). The biases of MIPAS measurements are ?0.39 K (?0.19%) and +0.25 K (+0.12%) (“+” positive bias, “?” negative bias) corresponding to the altitude regions 143–31 hPa (14–24 km) and 31–5 hPa (24–37 km), respectively.     

Variability of equatorial ionospheric electron density at fixed heights below the F2 peak

A study on variability of the equatorial ionosphere was carried out at fixed heights below the F2 peak for two different levels of solar activity. The study covered height range of 100 km up to the peak of F2 layer using a real height step increase of 10 km. The variability index used is the percentage ratio of standard deviation over the average value for the month. Daytime minimum variability of between 3% and 10% was observed at height range of about 150–210 km during low solar activity and between 2% and 7% at height range of 160–220 km during high solar activity. The nighttime maximum of between 70% and 187% was observed at height range of about 210–250 km during low solar activity and between 42% and 127% at height range of 210–250 km during high solar activity. The height range at which daytime minimum was observed falls within the F1 height of the ionosphere. The result obtained is consistent with previous works carried out in the low latitude locations for American sector.     

Young eclogite from the Greater Himalayan Sequence,Arun Valley,eastern Nepal: P–T–t path and tectonic implications

Garnet geochronology was used to provide the first direct measurement of the timing of eclogitization in the central Himalaya. Lu–Hf dates from garnet separates in one relict eclogite from the Arun River Valley in eastern Nepal indicate an age of 20.7 ± 0.4 Ma, significantly younger than ultra-high pressure eclogites from the western Himalaya, reflecting either different origins or substantial time lags in tectonics along strike. Four proximal garnet amphibolites from structurally lower horizons are 14–15 Ma, similar to post-eclogitization ages published for rocks along strike in southern Tibet. P–T calculations indicate three metamorphic episodes for the eclogite: i) eclogite-facies metamorphism at ～ 670 °C and ≥ 15 kbar at 23–16 Ma; ii) a peak-T granulite event at ～ 780 °C and 12 kbar; and iii) late-stage amphibolite-facies metamorphism at ～ 675 °C and 6 kbar at ～ 14 Ma. The garnet amphibolites were metamorphosed at ～ 660 °C. Three models are considered to explain the observed P–T–t evolution. The first assumes that the Main Himalayan Thrust (basal thrust of the Himalayan thrust system) cuts deeper at Arun than elsewhere. While conceptually the simplest, this model has difficulty explaining both the granulite-facies overprint and the pulse of exhumation between 25 and 14 Ma. A second model assumes that (aborted) subduction, slab breakoff, and ascent of India's leading edge occurred diachronously: ～ 50 Ma in the western Himalaya, ～ 25 Ma in the central Himalaya of Nepal, and presumably later in the eastern Himalaya. This model explains the P–T–t path, particularly heating during initial exhumation, but implies significant along-strike diachroneity, which is generally lacking in other features of the Himalaya. A third model assumes repeated loss of mantle lithosphere, first by slab breakoff at ～ 50 Ma, and again by delamination at ～ 25 Ma; this model explains the P–T–t path, but requires geographically restricted tectonic behavior at Arun. The P–T–t history of the Arun eclogites may imply a change in the physical state of the Himalayan metamorphic wedge at 16–25 Ma, ultimately giving rise to the Main Central Thrust by 15–16 Ma.