Statistical observations of spatial characteristics of Pi1B pulsations

We have examined the spatial and temporal correlation of high-latitude Pi1B and Pi2 pulsations, mid-latitude Pi2 pulsations, and auroral substorm onsets identified in the IMAGE far ultraviolet imager (FUV) data. Numerous search coil and fluxgate magnetometers at high latitudes (65–80° in Antarctica and Greenland) and mid-latitude fluxgate magnetometers are used. We find that Pi1B onset times agree well with onset times of intense isolated auroral substorms identified by the IMAGE FUV instrument: Pi1B onsets occurred within the 2 min cadence of the imager. For any given event, we find that Pi1B are localized to approximately 4 h of local time and 7° of magnetic latitude relative to the initial auroral brightening location as observed by IMAGE FUV. Not surprisingly, we also find that Pi1B pulsations occur typically between 2100 and 0200 MLT. Comparison to Pi2 records from these and other lower-latitude stations shows that in almost all cases Pi1B activity coincides within ±2 min with Pi2 activity. Power law fits showed that Pi1B amplitude fell off with distance^−2.9 for two strong events (i.e., similar to the r⁻³ falloff of the signal from a dipolar source), and only slightly more rapidly than the falloff of Pi2 activity (d^−2.8). Given the global nature of Pi2 pulsations versus the localized nature of Pi1B events in this study, we conclude that the mechanism that drives Pi1B pulsations is likely different from that responsible for Pi2 pulsations.     

Asymmetric response of the topside ionosphere to large-scale IGW generated during the November 30, 1979, substorm

We used bottomside ground observations and topside sounding data from the Intercosmos-19 satellite to study a Travelling Ionospheric Disturbance (TID) that occurred in response to Large-Scale Internal Gravity Wave (LSIGW) propagation during a substorm on November 30, 1979. We built a global scheme for the wavelike ionospheric variations during this medium substorm (AE_max ～800 nT). The area where the TID was observed looks like a wedge since it covers the nighttime hours at subauroral latitudes but contracts to a ～02 h local sector at low latitudes. The ionospheric response is strongly asymmetric because the wedge area and the TID amplitude are larger in the winter hemisphere than in the summer hemisphere. Clear evidence was obtained indicating that the more powerful TID from the Northern (winter) hemisphere propagated across the equator into the low latitude Southern (summer) hemisphere. Intercosmos-19 observations show that the disturbance covers the entire thickness of the topside ionosphere, from h_mF2 up to at least the 1000 km satellite altitude at post-midnight local times. F-layer lifting reached ～200 km, N_e increases in the topside ionosphere by up to a factor of ～1.9 and variations in N_mF2 of both signs were observed. Assumptions are made concerning the reason for the IGW effect at high altitudes in the topside ionosphere. The relationship between TID parameters and source characteristics determined from a global network of magnetometers are studied. The role of the dayside cusp in the generation of the TID in the daytime ionosphere is discussed. The magnetospheric electric field effects are distinguished from IGW effects.     

一次磁层亚暴期间磁场偶极化的尾向传播

利用TC1、Cluster和Polar结合极光和同步高度及地磁的观测,研究了2004年9月14日1730～1930 UT时间段的亚暴偶极化过程.此前行星际磁场持续南向几个小时.亚暴初发(Onset)开始于1823 UT.2 min之后,同步高度的LANL 02A在子夜附近观测到了明显的能量电子增强（Injection）事件,而TC1在1827UT左右在磁尾(-10,-2, 0)RE (GSE)观测到了磁场BX的突然下降,伴随着等离子体压强和温度的突然增加及磁场的强烈扰动.在(-16, 1, 3)RE (GSE) 的Cluster上相同的仪器观测到相同的现象,只是比TC1观测到的晚大约23 min,在1850 UT左右.虽然Polar在更靠近地球的较高纬度(-75, 35, -40)RE (GSE)附近,也在1855 UT左右观测到了这种磁场偶极化现象.以上的观测时序表明TC1、Cluster观测到的磁场偶极化比亚暴偶极化初始发生分别晚4 min和27 min.说明偶极化由近磁尾向中磁尾传播.详细计算表明偶极化源区的位置大约在X=-77RE～-86RE,而传播速度大约为70 km·s-1.在这个事件中亚暴的物理图像可能是中磁尾的近地重联产生的地向高速流到达近磁尾,为近磁尾的亚暴触发创造了条件;亚暴在近磁尾触发之后,磁场偶极化峰面向中磁尾传播.     

Detection of large scale TIDs associated with the dayside cusp using SuperDARN data

Variations in the dayside ionosphere parameters as a result of a large-scale acoustic gravity wave (LS AGW) were studied for the 17 February 1998 substorm using the super dual auroral radar network (SuperDARN) measurements. This event was characterised by a sharp rise in the AE index with a maximum of ～900 nT. The source of the disturbance responsible for the LS AGW appears to have been located within the plasma convection throat and in the dayside cusp region. The location of the source was obtained from studies of a number of datasets including high-latitude convection maps, data from 4 DMSP satellites and networks of ground-based magnetometers. The propagation of the LS AGWs caused quasi-periodic variations in the skip distance (with an amplitude up to 220–260 km) of the ground backscatter measured by up to 6 SuperDARN radars, including Goose Bay and Kapuskasing, resulting in two large-scale travelling ionospheric disturbances (LS TIDs). The LS TIDs had wave periods of 1.5 and 2 h, a velocity of ～400 m/s for both, and wavelengths of 2200 and 2900 km, respectively. These quasi-periodic variations were also present in the peak electron density and height of the F2 layer measured by the Goose Bay ionosonde. The numerical simulation of the inverse problem show good agreement between Goose Bay radar and Goose Bay ionosonde measurements. But these LS TIDs would be difficult to deduce from the ground based ionospheric station data alone, because h_mF2 variations were 10–40 km only and f_OF2 variations between 10% and 20%. The results demonstrate how important SuperDARN radars can be, and that this is a more powerful technique than routine ground-based sounding for studies of weak quasi-periodic variations in the dayside subauroral ionosphere related to LS AGW.     

Short time-scale impacts of hydropeaking on benthic invertebrates in an Alpine stream (Trentino,Italy)

The impact of a single hydropeaking event was studied in the Alpine stream Noce Bianco. Four stations were selected, one upstream and three, respectively, at 0.25, 6, and 8 km downstream from a hydropower plant. We collected drifting invertebrates during a planned water release that increased the discharge 7-fold. At the onset of the hydropeaking wave the number of invertebrates lost from the riverbed per minute to the drift increased 9-fold at the first downstream station and the same effects propagated 8 km downstream. The drift was composed mainly of aquatic insect larvae (Chironomidae, Plecoptera, Ephemeroptera Baetidae, and Psychodidae, with Chironomidae as the most abundant taxon at all stations) and partly by larval and adult riparian insects, and by Oligochaeta, which were particularly abundant at the station 6 km downstream. We monitored drift for 30 min from the start of the water release: peaks in drifting invertebrates occurred within 5–10 min of the beginning of the hydropeaking wave, and most of the invertebrates were washed out within the first 15 min of the water release. The different timeframes were possibly due to habitat preferences (most of the taxa that increased in the drift at the arrival of the wave were associated with algae and organic debris, which were washed off quickly by the increase in discharge) and/or behavioral adaptations (other taxa initially resisted the shear stress and began to drift with a delay of 5–10 min). The temporal pattern and drift composition corresponded well with those reported in literature, and indicate that repeated high-flow events of similar magnitude cause considerable losses from benthic populations to drift.     

Dynamics of North American sector ionospheric and thermospheric response during the November 2004 superstorm

We present a study of ionospheric and thermospheric response during a November 9–10, 2004 major geomagnetic storm event (DsT ～?300 nT). We utilize the North American sector longitude chain of incoherent scatter radars at Arecibo, Millstone Hill, and Sondrestrom, operating as part of a coordinated international mesosphere/lower thermosphere coupling study experiment. Total electron content (TEC) determinations from global positioning system (GPS) ground receivers, ground magnetometer traces from the Canadian CANOPUS array, Defense Meteorological Satellite Platform (DMSP) topside data, and global convection patterns from the SuperDARN radar network are analyzed to place the detailed radar data in proper mesoscale context. The plasmaspheric boundary layer (PBL) expanded greatly in the dusk sector during ring current intensification to span more than 25° of magnetic latitude, reaching as far south as 30° invariant latitude. Strong sub-auroral polarization stream velocities of more than 1 km/s were accompanied by large upwards thermal O+ fluxes to the overlying magnetosphere. The large PBL expansion subsequently exposed both Millstone Hill and Sondrestrom to the auroral convection pattern, which developed a complex multicell and reverse convection response under strongly northward IMF conditions during a period of global interplanetary electric field penetration. Large traveling atmospheric and ionospheric disturbances caused significant neutral wind and ion velocity surges in the mid-latitude and tropical ionosphere and thermosphere, with substorm activity launching equatorward neutral wind enhancements and subsequent mid-latitude dynamo responses at Millstone Hill. However, ionosphere and thermosphere observations at Arecibo point to significant disturbance propagation modification in the post-dusk sector PBL region.     

Sea level rise in the north-western part of the Arabian Gulf

Relative sea level variations in the north-western part of the Arabian Gulf have been estimated in the past using no more than 10 to 15 years of observations. In this study, we have almost doubled the period to 28.7 years by examining all available tide gauge data in the area and constructing a mean gauge time-series from seven coastal tide gauges. We found for the period 1979–2007 a relative sea level rise of 2.2 ± 0.5 mm/year. Using the subsidence observed at 6 GPS stations within a radius of 100 km of the tide gauges as an indication of the vertical land motion, the corresponding absolute sea level rise is 1.5 ± 0.8 mm/year that is in agreement with the global estimate of 1.9 ± 0.1 mm/year (Church and White, 2011) for the same studied period. By taking into account the temporal correlations we conclude that previous published results underestimate the true sea level rate uncertainty in this area by a factor of 5–10.     

Ten-year study of cloud-to-ground lightning activity in the Iberian Peninsula

The characteristics (annual and diurnal cycle, polarity, multiplicity and first stroke peak current) of ∼4.3×10⁶ cloud-to-ground flashes recorded in the Iberian Peninsula during the first decade of measurements of the lightning detection network installed in Spain are analyzed. The mean monthly variation shows maximum lightning activity between May and September, while minimum values are observed in January and February. The mean diurnal cycle shows maximum values at 1700 LT and minimum values at around 1000 LT. The average maximum flash density (not corrected for detection efficiency) is 2.1 flashes km⁻² year⁻¹. Maximum lightning activity is associated with mountainous areas. The effect of the Mediterranean Sea is also seen. The percentage of positive flashes is 9%, although this changes over the year from 6.5% in June to 22.6% in January. The average multiplicity is found to be 2.0 for the negative flashes and 1.1 for the positive flashes, and the percentages of single-stroke flashes are 53.6% and 89%, respectively. The monthly distribution of multiplicity for negative flashes peaks in the summer and minimum values are found in the winter. The multiplicity of the positive flashes does not seem to be function of the month. The median (mean) first stroke peak currents are found to be 23.5 kA (27.3 kA) for the negative flashes and 35.3 kA (47.1 kA) for the positive flashes. For both polarities, the peak current is higher in the summer than in the winter. The percentage of positive flashes and the mean peak currents for negative flashes are higher over the sea areas than over land.     

Substorm observations in the early morning sector with Equator-S and Geotail

Data from Equator-S and Geotail are used to study the dynamics of the plasma sheet observed during a substorm with multiple intensifications on 25 April 1998, when both spacecraft were located in the early morning sector (03–04 MLT) at a radial distance of 10–11 R_E. In association with the onset of a poleward expansion of the aurora and the westward electrojet in the premidnight and midnight sector, both satellites in the morning sector observed plasma sheet thinning and changes toward a more tail-like field configuration. During the subsequent poleward expansion in a wider local time sector (20−04 MLT), on the other hand, the magnetic field configuration at both satellites changed into a more dipolar configuration and both satellites encountered again the hot plasma sheet. High-speed plasma flows with velocities of up to 600 km/s and lasting 2–5 min were observed in the plasma sheet and near its boundary during this plasma sheet expansion. These high-speed flows included significant dawn-dusk flows and had a shear structure. They may have been produced by an induced electric field at the local dipolarization region and/or by an enhanced pressure gradient associated with the injection in the midnight plasma sheet.     

Relationship between the PC and AL indices during repetitive bay-like magnetic disturbances in the auroral zone

To study the relations of the polar cap (PC) magnetic activity (characterized by the PC index) to magnetic disturbances in the auroral zone (AL index) the behavior of 62 repetitive bay-like magnetic disturbances has been analyzed. It was found that the PC index, derived as a proxy of the geoeffective interplanetary electric field Em, starts to increase, on average, about 30 min ahead of the magnetic disturbance onset. Value of Em and PC～2 mV/m seems to be necessary for development of the repetitive bay-like disturbances with peak AL exceeding 400 nT. Growth phase duration (the time interval between the start of PC increase and AL sudden onset) and intensity of magnetic disturbances in the auroral zone (AL max) highly correlate with the PC growth rate. The growth phase reduces to a few minutes, if the PC index suddenly jumps above ～6–8 mV/m. The sharp development of Birkeland current wedge during expansion phase insignificantly influences the polar cap activity: the corresponding PC index increase does not exceed 10–20% of the PC value. It is concluded that the PC index may be considered as a convenient proxy of the solar wind energy input into the magnetosphere.     

Anomalous cosmogenic 3He production and elevation scaling in the high Himalaya

The production rate of cosmogenic ³He in apatite, zircon, kyanite and garnet was obtained by cross-calibration against ¹⁰Be in co-existing quartz in glacial moraine boulders from the Nepalese Himalaya. The boulders have ¹⁰Be ages between 6 and 16 kyr and span elevations from 3200 to 4800 m. In all of these minerals ³He correlates with ¹⁰Be and is dominantly cosmogenic in origin. After modest correction for non-cosmogenic components, ³He/¹⁰Be systematics imply apparent sea-level high-latitude (SLHL) apparent production rates for ³He of 226 atoms g^? 1 yr^? 1 in zircon, 254 atoms g^? 1 yr^? 1 in apatite, 177 atoms g^? 1 yr^? 1 in kyanite, and 153 atoms g^? 1 yr^? 1 in garnet. These production rates are unexpectedly high compared with rates measured elsewhere in the world, and also compared with proposed element-specific production rates. For apatite and zircon, the data are sufficient to conclude that the ³He/¹⁰Be ratio increases with elevation. If this reflects different altitudinal scaling between production rates for the two isotopes then the SLHL production rates estimated by our approach are overestimates. We consider several hypotheses to explain these observations, including production of ³He via thermal neutron capture on ⁶Li, altitudinal variations in the energy spectrum of cosmic-ray neutrons, and the effects of snow cover. Because all of these effects are small, we conclude that the altitudinal variations in production rates of cosmogenic ³He and ¹⁰Be are distinct from each other at least at this location over the last ～ 10 kyr. This conclusion calls into question commonly adopted geographic scaling laws for at least some cosmogenic nuclides. If confirmed, this distinction may provide a mechanism by which to obtain paleoelevation estimates.     

Hydrological effects on gravity and correlations between gravitational variations and level of the Alzette River at the station of Walferdange,Luxembourg

The gravitational effects of water storage variations driven by local precipitation events are modeled for the Walferdange Underground Laboratory for Geodynamics (WULG) in the Grand Duchy of Luxembourg. A modified mass continuity model is implemented, which uses rainfall data from Walferdange as input. In the absence of soil moisture and groundwater level information, the model is empirically parameterized. Model outputs are compared to the gravity time series registered with the Observatory Superconducting Gravimeter CT040 located in the WULG. We find that the model explains 77% of the gravity residuals. In addition, a statistical analysis is carried out to determine the relationship between precipitation, gravity variations and water level changes in the nearby Alzette River. A time delay of 88 ± 34 min between the maximum variation rates of the water level and gravity signal has been calculated. The signals have an admittance of 45 ± 5 cm μGal^?1.     

Prediction of the consumption rates for juvenile Atlantic salmon (Salmo salar L.) on the scale of habitat patches: Development of empirical models based on stomach contents

Rivers and streams are unstable environments in which estimation of energetic costs and benefits of habitat utilization are the daunting exercise. Empirical models of food consumption may be used to estimate energetic benefits based on abiotic and biotic conditions in patches of habitat. We performed thirty daily surveys of fish stomach contents to estimate the consumption rates for juvenile Atlantic salmon (Salmo salar) in a river. The data were used to assess whether variations of daily consumption rates existed within the river, and to develop empirical models that could predict fish consumption rates using abiotic and biotic conditions as independent variables. Daily consumption rates based on stomach content surveys in the field (range: 0.15–1.49 g dry/(100 g wet day)) varied significantly depending on habitat patch (500–1000 m²), summer period, and sampling year. Variables such as water temperature, numerical density of salmon, water depth and moon phase explained 83–93% of the variations in daily food consumption rates. Daily consumption rates tended to increase with water temperature and depth, and were also higher near a full moon. However, they tended to decrease with the numerical density of salmon. Our work suggests that empirical models based on independent variables that are relatively simple to estimate in the field may be developed to predict fish consumption rates in different habitat patches in a river.     

Evaluation of energetic particle parameters in the near-Earth magnetotail derived from flux asymmetry observations

The flux asymmetries measured by spectrometers on board spacecraft contain information on particle parameters. The net flux intensity (NFI) method provides a tool to evaluate these parameters. The NFI method is valid when both the spin period of the spacecraft and the time resolution of the particle spectrometers are much shorter than the characteristic time-scale of the particle flux variations. We apply the NFI analysis to the flux asymmetry measurements made by GEOS 2 at the nightside geosynchronous orbit in the late substorm growth phase. The cross-tail current of energetic ions, their pressure gradient and average drift velocity, as well as a field-aligned flows are investigated. Current disruption at substorm onset and the –convection surge mechanism during dipolarization of the magnetic field are directly observed.     

Cave air ventilation and CO2 outgassing by radon-222 modeling: How fast do caves breathe?

In general, the rate and timing of calcite precipitation is in part affected by variations in cave air CO₂ concentrations. Knowledge of cave ventilation processes is required to quantify the effect variations in CO₂ concentrations have on speleothem deposition rates and thus paleoclimate records. In this study we use radon-222 (²²²Rn) as a proxy of ventilation to estimate CO₂ outgassing from the cave to the atmosphere, which can be used to infer relative speleothem deposition rates. Hollow Ridge Cave, a wild cave preserve in Marianna, Florida, is instrumented inside and out with multiple micro-meteorological sensor stations that record continuous physical and air chemistry time-series data. Our time series datasets indicate diurnal and seasonal variations in cave air ²²²Rn and CO₂ concentrations, punctuated by events that provide clues to ventilation and drip water degassing mechanisms. Average cave air ²²²Rn and CO₂ concentrations vary seasonally between winter (²²²Rn = 50 dpm L^? 1, where 1 dpm L^? 1 = 60 Bq m^? 3; CO₂ = 360 ppmv) and summer (²²²Rn = 1400 dpm L^? 1; CO₂ = 3900 ppmv). Large amplitude diurnal variations are observed during late summer and autumn (²²²Rn = 6 to 581 dpm L^? 1; CO₂ = 360 to 2500 ppmv).We employ a simple first-order ²²²Rn mass balance model to estimate cave air exchange rates with the outside atmosphere. Ventilation occurs via density driven flow and by winds across the entrances which create a ‘venturi’ effect. The most rapid ventilation occurs 25 m inside the cave near the entrance: 45 h^? 1 (1.33 min turnover time). Farther inside (175 m) exchange is slower and maximum ventilation rates are 3 h^? 1 (22 min turnover time). We estimate net CO₂ flux from the epikarst to the cave atmosphere using a CO₂ mass balance model tuned with the ²²²Rn model. Net CO₂ flux from the epikarst is highest in summer (72 mmol m^? 2 day^? 1) and lowest in late autumn and winter (12 mmol m^? 2 day^? 1). Modeled ventilation and net CO₂ fluxes are used to estimate net CO₂ outgassing from the cave to the atmosphere. Average net CO₂ outgassing is positive (net loss from the cave) and is highest in late summer and early autumn (about 4 mol h^? 1) and lowest in winter (about 0.5 mol h^? 1). Modeling of ventilation, net CO₂ flux from the epikarst, and CO₂ outgassing to the atmosphere from cave monitoring time-series can help better constrain paleoclimatic interpretations of speleothem geochemical records.     

Crustal structure of the Reykjanes Ridge near 62°N,on the basis of seismic refraction and gravity data

Explosion deep seismic sounding data sections of high quality had been obtained with RV Meteor in the Reykjanes Iceland Seismic Project (RRISP77 [Angenheister, G., Gebrande, H., Miller, H., Goldflam, P., Weigel, W., Jacoby, W.R., Pálmason, G., Björnsson, S., Einarsson, P., Pavlenkova, N.I., Zverev, S., Litvinenko, I.V., Loncarecic, B., Solomon, S., 1980. Reykjanes Ridge Iceland Seismic Experiment (RRISP 77). J. Geophys. 47, 228–238]) which close an information gap near 62°N. Preliminary results were presented by Weigel [Weigel, W., 1980. Aufbau des Reykjanes Rückens nach refraktionsseismischen Messungen. In: Weigel, W. (Ed.), Reykjanes Rücken, Island, Norwegischer Kontinentalrand. Abschlusskolloquium, Hamburg zur Meteor-Expedition, vol. 45. DFG, Bonn, pp. 53–61], and here we report on the data and results of interpretation. Clear refracted phases to 90 km distance permit crustal and uppermost mantle structure to be modelled by ray tracing. The apparent P-wave velocities are around 4.5, 6–6.5, 7–7.6 and 8.2–8.7 km/s, but no wide-angle reflections have been clearly seen. Accompanying sparker reflection data reveal thin sediment ponds in the axial zone and up to 400 m thick sediments at 10 Ma crustal age. Ray tracing reveals the following model below the sediments: (1) a distinct, 1–2 km thick upper crust (layer 2A) with Vp increasing with age (to 10 Ma) from <3.4 to 4.9 km/s and with a vertical gradient of 0.1–0.2 km/s/km, (2) a lower crust or layer 3 beginning at depths of 2 (axis) to 4 km (10 Ma age) below sea level with 6.1–6.8 km/s and similar vertical gradients as above, (3) the lower crust bottoms at 5.2–9.5 km depth below sea level (0–10 Ma) with a marked discontinuity, underneath which (4) Vp rises from about 7.5–7.8 km/s (0–10 Ma) with a positive vertical gradient of, again, 0.1–0.2 km/s/km such that 8 km/s would be reached at 12 km and deeper near the axis. Our preferred interpretation is that the mantle begins at the distinct discontinuity (“Moho”), but a deeper “Moho” of Vp ≈ 8 km/s cannot be excluded. From Iceland southward to 60°N several experiments show a decrease of crustal thickness from 14 to 8 km. Velocity trends with age across the ridge reflect cooling and filling of cracks, and thickness trends probably suggest volcanic productivity variations as previously suggested.Gravity inversion concentrates on a profile across the ridge with the above seismic a priori information; with 0.2–0.5 km depth uncertainty it leads to a good fit (±2.5 mGal where seismic data exist). Best fitting densities are (in kg/m³) for sediments, 2180; upper crust, 2450–2570; lower crust, 2850–2940; mantle lithosphere, 3215–3240 with a deficit for an asthenospheric wedge of no more than −100 kg/m³. The morphological ridges and troughs superimposed on the SE ridge flank are partly correlated, partly anti-correlated with the Bouguer anomaly and suggest that variable crustal density variations accompany the morphology variations.     

Climatology of total electron content near the dip equator under geomagnetic quiet-conditions

This study analyzes the TEC data during 1998–2007, observed by the AREQ (16.5°S, 71.5°W) GPS station to investigate the equatorial ionospheric variations under geomagnetic quiet-conditions. The diurnal TEC values generally have a maximum value between 1330 and 1500 LT and a minimum around 0500 LT. For the seasonal variation, the semi-annual variation apparently exists in the daytime TEC with two peaks in equinoctial months. In contrast, this semi-annual variation is not found in the nighttime. Furthermore, the results of the annual variation show that the correlation between the daytime TEC value and the solar activity factor is highly positive.     

Diurnal variations of the total electron content under quiet helio-geomagnetic conditions

The morphology of averaged diurnal variations of total electron content (TEC) under quiet helio-geomagnetic conditions for all latitudinal bands and various longitudes has been studied using Global Ionospheric Maps (GIMs) datasets. The diurnal TEC variation maximum is generally registered at 14–15 LT. The maximum is 38±5, 14±2, 10±2 TECU (TECU is generally accepted TEC unit) at the equatorial, middle and high latitudes. The nighttime TEC minimum is within 5–7 TECU regardless of a season, latitude and longitude. At the equatorial latitudes TEC exhibits the most significant daily/season variations and the asymmetry of its behavior in the hemispheres near the equinox. Abnormal diurnal TEC variations (evening maximum, near-noon minimum) are observed at middle and high latitudes in summer due to atmospheric wind effects. The comparison of the averaged diurnal TEC variations with the behavior of the ionospheric F2-layer critical frequency indicated that GIMs describe daily/annual TEC variations reasonably well.     

First results on determination of cosmogenic 36Cl in limestone from the Yenicekale Complex in the Hittite capital of Hattusha (Turkey)

We have measured ³⁶Cl in three rock surfaces of the Yenicekale building complex in Hattusha (Bo?azköy, Turkey). Hattusha was the capital of Hittite Empire which lasted from about 1650/1600 to 1200 BC. At Yenicekale, Hittite masons flattened the summit of an outcropping limestone knoll to form an artificial platform as the foundation for a building. Next they built a circuit wall along the lateral precipices of the flattened bedrock platform. We took one sample from the limestone bedrock platform and two samples from limestone building blocks of the circuit wall for cosmogenic ³⁶Cl analysis. Calculated exposure ages are 20 ± 1 ka for the sample from the bedrock platform and 24 ± 1 ka and 52 ± 2 ka for the circuit wall blocks. These exposure ages are significantly older than the age expected based on the estimated time of construction between 3.2 ka and 3.7 ka. We conclude that the sampled surfaces contain significant inherited cosmogenic ³⁶Cl. We cannot directly determine exposure ages for the building complex based on these three samples. On the other hand we may use the measured concentrations to determine how much of the rock was removed from the platform during flattening. To this end we modeled the variation of ³⁶Cl production with depth at Yenicekale using the results from the bedrock sample. We conclude that the Hittite masons removed only around 3 m from top of the limestone block. This means that the volume of rock removed from the bedrock platform is significantly less than the volume in the circuit wall atop the platform. They did not gain enough rock from this flattening to make the building. In agreement with this, the first results of our detailed microfacies analysis indicate that many of the building blocks are not of the same facies as the underlying limestone and must have been quarried elsewhere. Although we were not able to exposure date the Yenicekale complex due to the presence of inherited ³⁶Cl, our data suggest that Hittite masons excavated (most of) the building stones not at Yenicekale, but in quarries outside of Hattusha and then transported them to the construction site. These quarries have not yet been identified.     

Water mass variation in the Mediterranean and Black Seas

The mass-induced sea level variability and the net mass transport between Mediterranean Sea and Black Sea are derived for the interval between August 2002 and July 2008 from satellite-based observations and from model data. We construct in each basin two time series representing the basin mean mass signal in terms of equivalent water height. The first series is obtained from steric-corrected altimetry while the other is deduced from GRACE data corrected for the contamination by continental hydrology. The series show a good agreement in terms of annual and inter-annual signals, which is in line with earlier works, although different model corrections influence the consistency in terms of seasonal signal and trend.In the Mediterranean Sea, we obtain the best agreement using a steric correction from the regional oceanographic model MFSTEP and a continental hydrological leakage correction derived from the global continental hydrological model WaterGAP2. The inter-annual time series show a correlation of 0.85 and a root mean square (RMS) difference of 15 mm. The two estimates have similar accuracy and their annual amplitude and phase agree within 3 mm and 23 days respectively. The GRACE-derived mass-induced sea level variability yields an annual amplitude of 27 ± 5 mm peaking in December and a trend of 5.3 ± 1.9 mm/yr, which deviates within 3 mm/yr from the altimetry-derived estimate.In the Black Sea, the series are less consistent, with lower accuracy of the GRACE-derived estimate, but still show a promising agreement considering the smaller size of the basin. The best agreement is realized choosing the corrections from WaterGAP2 and from the regional oceanographic model NEMO. The inter-annual time series have a correlation and RMS differences of 0.68 and 55 mm, their annual amplitude and phase agree within 4 mm and 6 days respectively. The GRACE-derived seawater mass signal has an annual amplitude of 32 ± 4 mm peaking in April. On inter-annual time scales, the mass-induced sea level variability is stronger than in the Mediterranean Sea, with an increase from 2003 to 2005 followed by a decrease from 2006 to 2008.Based on mass conservation, the mass-induced sea level variations, river runoff and precipitation minus evaporation are combined to derive the strait flows between the basins and with the Atlantic Ocean. At the Gibraltar strait, the net inflow varies annually with an amplitude of 52 ± 10 × 10⁻³ Sv peaking end of September (1 Sv = 10⁶ m³ s⁻¹). The inflow through the Bosphorus strait displays an annual amplitude of 13 ± 3 ×10⁻³ Sv peaking in the middle of March. Additionally, an increase of the Gibraltar net inflow (3.4 ± 0.8 × 10⁻³ Sv/yr) is detected.