Ionospheric effetcs of an intense geomagnetic storm

An investigation of the response of the mid-high, mid and low latitude critical frequency foF2 to the geomagnetic storm of 15 July 2000 is made. Ground-based hourly foF2 values (proportional to square root of peak electron density of F2-layer) from four chains of ionospheric stations located in the geographic longitude ranges 10°W–35°E, 60°E–120°E, 130°E–170°E, 250°E–295°E are used. Relative deviations of foF2 are considered. The main ionospheric effects for the considered storm are: long-duration negative disturbances at mid-high latitudes in summer hemisphere in sectors where the storm onset occurred in the afternoon/night-time hours; short-duration positive disturbances in the summer hemisphere at mid-high latitudes in the pre-sunset hours during the end of main phase-first stage of the recovery; small and irregular negative disturbances in the low latitude winter hemisphere which predominate during the main phase and first part of the recovery, and positive disturbances in both hemispheres at mid-high and mid latitudes prior to the storm onset irrespective of the local time. In addition, the validity of some physical mechanisms proposed to explain the F2 region behaviour during disturbed conditions is considered. gus-mansilla@hotmail.com     

Predictability of Indian Monsoon Circulation with High Resolution ECMWF Model in the Perspective of Tropical Forecast During the Tropical Convection Year 2008

To address some of the issues of project Year of Tropical Convection (YOTC) and the project ATHENA as ongoing international activities, an endeavor has been made for the first time to study the predictability of Indian summer monsoon in the backdrop of tropical predictability using 850 hPa atmospheric circulations with the high resolution (T1279) ECMWF model during the boreal summer of 2008 as one of the focus years of YOTC. The major findings obtained from the statistical forecast have been substantiated by the dynamical prediction in terms of the systematic error energy, its growth rate and the attribution of the dominant nonlinear dynamical processes to error growth. The systematic error energy of T1279 (16 km resolution) ECMWF model are generated in African landmass, India and its adjoining oceanic region, in near equatorial west Pacific and around the Madagascar region where the root mean square errors are observed and the zonal wind anomaly shows poor forecast skill. As far as the inadequate predictability of Indian summer monsoon by T1279 ECMWF model (revealed from the results of project ATHENA) is concerned, the systematic error energy and the error growth over Arabian Sea, in the eastern and western India due to the nonlinear convergence and divergence of error flux along with the erroneous Mascarene high may possibly be the determining factors for not showing any discernable improvement in Indian monsoon during the medium range forecast up to 240 h. This work suggests that the higher resolution of ECMWF model may not necessarily lead to the better forecast of Indian monsoon circulations during 2008 unless a methodology can be devised to isolate the errors due to the nonlinear processes that are inherent within the system.     

Estimation of atmospheric predictability for multivariable system using information theory in nonlinear error growth dynamics

To estimate atmospheric predictability for multivariable system, based on information theory in nonlinear error growth dynamics, a quantitative method is introduced in this paper using multivariable joint predictability limit (MJPL) and corresponding single variable predictability limit (SVPL). The predictability limit, obtained from the evolutions of nonlinear error entropy and climatological state entropy, is not only used to measure the predictability of dynamical system with the constant climatological state entropy, but also appropriate to the case of climatological state entropy changed with time. With the help of daily NCEP-NCAR reanalysis data, by using a method of local dynamical analog, the nonlinear error entropy, climatological state entropy, and predictability limit are obtained, and the SVPLs and MJPL of the winter 500-hPa temperature field, zonal wind field and meridional wind field are also investigated. The results show that atmospheric predictability is well associated with the analytical variable. For single variable predictability, there exists a big difference for the three variables, with the higher predictability found for the temperature field and zonal wind field and the lower predictability for the meridional wind field. As seen from their spatial distributions, the SVPLs of the three variables appear to have a property of zonal distribution, especially for the meridional wind field, which has three zonal belts with low predictability and four zonal belts with high predictability. For multivariable joint predictability, the MJPL of multivariable system with the three variables is not a simple mean or linear combination of its SVPLs. It presents an obvious regional difference characteristic. Different regions have different results. In some regions, the MJPL is among its SVPLs. However, in other regions, the MJPL is less than its all SVPLs.     

初值和海温强迫对延伸期可预报性时空分布的影响

利用全球谱模式T106L19和增长模繁殖法,分别在气候海温和预测海温强迫下,进行了动力延伸集合预报试验.基于方差分析思想,利用集合预报结果,定义和计算了初值影响指数、海温强迫影响指数、潜在可预报性指数以及波动活动指数.通过分析四个指数,揭示了初值和海温强迫对延伸期可预报性时空分布以及潜在可预报性的影响,并探讨了其影响机理.结果表明：初值影响指数分布具有地域和季节的差异,初值的影响在中高纬度地区大于热带地区;相同季节,海温强迫影响指数分布与初值影响指数分布相似;潜在可预报性指数呈带状分布,大值集中在热带地区,且在低纬度地区,高层的潜在可预报性大于低层;初值和海温强迫对延伸期可预报性时空分布的影响,依赖于大气环流形势,初值和海温强迫影响的显著区正是大气长波的活跃区和西风急流区,急流区的强风切变为长波活动提供了斜压不稳定能量,而长波的发展调控着初值和海温强迫的影响,这说明延伸期的可预报性具有明显的流依赖性,大气外强迫的作用也与大气内部的动力过程密切相关.     

Dynamics of hourly sea level at Hillarys Boat Harbour,Western Australia: a chaos theory perspective

Water level forecasting using recorded time series can provide a local modelling capability to facilitate local proactive management practices. To this end, hourly sea water level time series are investigated. The records collected at the Hillarys Boat Harbour, Western Australia, are investigated over the period of 2000 and 2002. Two modelling techniques are employed: low-dimensional dynamic model, known as the deterministic chaos theory, and genetic programming, GP. The phase space, which describes the evolution of the behaviour of a nonlinear system in time, was reconstructed using the delay-embedding theorem suggested by Takens. The presence of chaotic signals in the data was identified by the phase space reconstruction and correlation dimension methods, and also the predictability into the future was calculated by the largest Lyapunov exponent to be 437 h or 18 days into the future. The intercomparison of results of the local prediction and GP models shows that for this site-specific dataset, the local prediction model has a slight edge over GP. However, rather than recommending one technique over another, the paper promotes a pluralistic modelling culture, whereby different techniques should be tested to gain a specific insight from each of the models. This would enable a consensus to be drawn from a set of results rather than ignoring the individual insights provided by each model.     

Conditional nonlinear optimal perturbation: Applications to stability,sensitivity, and predictability

Conditional nonlinear optimal perturbation (CNOP) is a nonlinear generalization of linear singular vector (LSV) and features the largest nonlinear evolution at prediction time for the initial perturbations in a given constraint. It was proposed initially for predicting the limitation of predictability of weather or climate. Then CNOP has been applied to the studies of the problems related to predictability for weather and climate. In this paper, we focus on reviewing the recent advances of CNOP’s applications, which involves the ones of CNOP in problems of ENSO amplitude asymmetry, block onset, and the sensitivity analysis of ecosystem and ocean’s circulations, etc. Especially, CNOP has been primarily used to construct the initial perturbation fields of ensemble forecasting, and to determine the sensitive area of target observation for precipitations. These works extend CNOP’s applications to investigating the nonlinear dynamical behaviors of atmospheric or oceanic systems, even a coupled system, and studying the problem of the transition between the equilibrium states. These contributions not only attack the particular physical problems, but also show the superiority of CNOP to LSV in revealing the effect of nonlinear physical processes. Consequently, CNOP represents the optimal precursors for a weather or climate event; in predictability studies, CNOP stands for the initial error that has the largest negative effect on prediction; and in sensitivity analysis, CNOP is the most unstable (sensitive) mode. In multi-equilibrium state regime, CNOP is the initial perturbation that induces the transition between equilibriums most probably. Furthermore, CNOP has been used to construct ensemble perturbation fields in ensemble forecast studies and to identify sensitive area of target observation. CNOP theory has become more and more substantial. It is expected that CNOP also serves to improve the predictability of the realistic predictions for weather and climate events plays an increasingly important role in exploring the nonlinear dynamics of atmospheric, oceanic and coupled atmosphere-ocean system. Supported by National Basic Research Program of China (Grant Nos. 2006CB403606, 2007CB411800), National Natural Science Foundation of China (Grant Nos. 40830955, 40675030, 40505013), Institute of Atmospheric Physics, Chinese Academy of Sciences (Grant No. IAP07202), and LASG State Key Laboratory Special Fund     

A study on chaotic behaviour of equatorial/low latitude ionosphere over Indian subcontinent,using GPS-TEC time series

The deterministic chaotic behaviour of ionosphere, over Indian subcontinent falling under equatorial/low latitude region, ?0.3 to 22.19°N (geomagnetic), was studied using GPS-TEC time series. The values of Lyapunov exponent are low at Thiruvananthapuram and Agatti (?0.30 and 2.38°N, geomagnetic, respectively), and thereafter increase through Bangalore and Hyderabad (4.14 and 8.54°N, geomagnetic, respectively), and attain maximum at Mumbai (10.09°N, geomagnetic), which is near/at the edge of an anomaly crest. The values of correlation dimension computed for TEC time series are in the range 3.1–3.6, which indicate that equatorial/low latitude ionosphere can be described with four variables. Entropy values estimated for TEC time series show no appreciable latitudinal variabilites. The values of non-linear prediction error exhibit a trough, around the latitude sector, 4.14–16.15°N (Geomagnetic). Based on the values of the above quantifiers, the features of chaotic behaviour of equatorial/low latitude ionosphere are briefly discussed.     

Seasonal,longitudinal, and latitudinal differences in air temperatures in Russia in years of sunspot maxima and minima

Based on an analysis of a large array of meteorological data, we have shown that surface air temperatures differ significantly in years of sunspot maxima and minima for different months and latitudes and longitudes of observation points. This difference is the greatest at high latitudes of 60–83°; it is equal to +2.07 ± 0.28°C in February in the longitudinal range of 170 ± 190° and −1.41 ± 0.29°C in November in the longitude range of 150 ± 170°.     

Interannual variability of Antarctic Oscillation and its influence on East Asian climate during boreal winter and spring

1 Introduction Antarctic Oscillation is a major mode of Southern Hemispheric (SH) extratropical atmospheric circula- tion. The SH Annual Mode represents a zonally sym- metric exchange of mass between polarward of 60°S and 40°S[1], therefore AAO indicates both the intensity of circumpolar low and zonal mean west wind at mid-high latitudes in SH. Positive phase of AAO tends to deepen circumpolar low and enhance west wind at mid-high latitudes in SH. Many studies show that AAO has bar…     

Morphology and causes of the Weddell Sea anomaly

The zone of anomalous diurnal variations in foF2, which is characterized by an excess of nighttime foF2 values over daytime ones, has been distinguished in the Southern Hemisphere based on the Intercosmos-19 satellite data. In English literature, this zone is usually defined as the Weddell Sea anomaly (WSA). The anomaly occupies the longitudes of 180°–360° E in the Western Hemisphere and the latitudes of 40°–80° S, and the effect is maximal (up to ∼5 MHz) at longitudes of 255°–315° E and latitudes of 60°–70° S (50°–55° ILAT). The anomaly is observed at all levels of solar activity. The anomaly formation causes have been considered based on calculations and qualitative analysis. For this purpose, the longitudinal variations in the ionospheric and thermospheric parameters in the Southern Hemisphere have been analyzed in detail for near-noon and near-midnight conditions. The analysis shows that the daytime foF2 values are much smaller in the Western Hemisphere than in the Eastern one, and, on the contrary, the nighttime values are much larger, as a result of which the foF2 diurnal variations are anomalous. Such a character of the longitudinal effect mainly depends on the vertical plasma drift under the action of the neutral wind and ionization by solar radiation. Other causes have also been considered: the composition and temperature of the atmosphere, plasma flows from the plasmasphere, electric fields, particle precipitation, and the relationship to the equatorial anomaly and the main ionospheric trough.     

Longitudinal variations in the daytime low-latitude ionosphere according to the data of topside sounding from the intercosmos-19 satellite

Using the data of the topside ionosphere sounding from the Intercosmos-19 satellite, longitudinal variations in foF2 at low latitudes at the daytime hours are considered. It is obtained that these variations in particular days in the majority of cases have a regular wave-like character with periods of about 75°–100° in longitude and amplitudes on the average of 2–4 MHz. In other words, along the valley and crests of the equatorial anomaly, a structure with four maximums and four minimums which have a tendency to be located near certain longitudes (the same in all seasons) is observed. The variations in foF2 along the crests of the equatorial anomaly are usually in anti-phase to variations along its valley. Comparing the characteristics of this wavelike structure at the daytime and nighttime hours, we obtained that the average positions of its extremes at the nighttime hours are shifted eastwards by 10°–50° relative to the daytime extremes. As a cause of formation of such a structure, high harmonics of atmospheric tides are assumed which, uplifting from below to heights of the E region, via the electric currents in this region influence the longitudinal structure of the electrodynamic plasma drift over the equator and by that impact the structure of the entire daytime low-latitude ionosphere.     

Variations in the near-surface atmospheric electric field at high latitudes and ionospheric potential during geomagnetic perturbations

We have analyzed variations in the near-surface atmospheric electric field (Ez) normalized to their daily averages that were simultaneously observed in different high-latitude regions at moderate geomagnetic activity (Kp ∼ 3). The Ez data were measured under fair weather conditions at the Vostok Antarctic research station (Φ′ = −83.5°) in the southern polar cap and at the Hornsund Arctic observatory (Φ′ = 74.0°) on Svalbard close to the polar boundary of the auroral oval in the Northern Hemisphere. It is established that variations in the atmospheric electric field in the polar cap region at the Vostok station are controlled (the correlation coefficient R ∼ 0.7–0.9) by variations in the overhead ionospheric potential. The situation at the Hornsund observatory is more complicated. During intervals when Hornsund occurred below the westward electrojet, the correlation was typically positive with R ∼ 0.60–0.85; however, while this observatory was in the region of the eastern electrojet, the correlation could be negative with R ∼ 0.7–0.8. Normally, during such periods, the westward electrojet was detected polarwards of Hornsund while, according to the SuperDARN radar data, the observatory was located below the negative vortex of the polar ionospheric convection.     

Predictable component analysis of a system based on nonlinear error information entropy

Based on the theory of information entropy concerning nonlinear errors,the growth rules for the nonlinear errors of the Lorenz system and its predictable components are studied.The results show that the impact of the uncertainties,both in the initial error and in the system itself,needs to be considered in a quantitative estimation of the system predictability.The nonlinear error growth is related to the magnitude of the initial error,and to the spatial distribution of the initial error vectors.Even if these initial errors have the same magnitude but different directions,there are also differences in the nonlinear error growth.The predictability of nonlinear error growth is related to the error component,but not related to the ratio of these components.The component with the highest/lowest rate of contribution does not necessarily have the greatest/least predictability.The different components have different predictabilities,and in different time periods,the different predictable components also have different predictabilities.     

Evidence of geomagnetic storm effects in the lower atmosphere: A case study

Disturbances produced by geomagnetic storms in the higher regions of the Earth’s atmosphere, such as in the ionospheric F2 region and in the lower ionosphere, are relatively better known than those produced at lower altitudes, where the effects of geomagnetic storms have been little studied. During magnetically perturbed conditions, some changes in pressure and temperature at high latitudes have been observed, from the surface level to heights of around 30 km, but there are no morphological studies and/or patterns of behavior. Moreover, the physical mechanisms are still unknown and what exists is a matter of controversy. Thus, the aim of this paper is to contribute to the vertical profile of the effects of geomagnetic storms as observed in the lower sectors of the atmosphere. For that, we study the variations of two atmospheric parameters (temperature and wind speed) during an intense geomagnetic storm (minimum Dst = −300 nT), at heights between about 6 km and 20 km. The data used were obtained from weather balloon flights carried out at low, mid and mid-high latitudes in different longitudinal sectors of the northern hemisphere, which took place twice per day: 00:00 and 12:00 UT. Small, but statistically significant changes in temperature and in zonal component of the neutral winds are observed at mid-high latitudes, which can be linked to short-term geomagnetic forcing. However, the results show different atmospheric response to the geomagnetic storm in the different longitudinal sectors at tropospheric and stratospheric levels, which suggests a regional character of the geomagnetic storms effects at tropospheric levels.     

Rhyolite magma degassing: an experimental study of melt vesiculation

 The vesiculation of a peralkaline rhyolite melt (initially containing ∼0.14 wt.% H₂O) has been investigated at temperatures above the rheological glass transition (T _g≈530  °C) by (a) in situ optical observation of individual bubble growth or dissolution and (b) dilatometric measurements of the volume expansion due to vesiculation. The activation energy of the timescale for bubble growth equals the activation energy of viscous flow at relatively low temperatures (650–790  °C), but decreases and tends towards the value for water diffusion at high temperatures (790–925  °C). The time dependence of volume expansion follows the Avrami equation ΔV (t)∼{1–exp [–(t/τ_av) ⁿ ]} with the exponent n=2–2.5. The induction time of nucleation and the characteristic timescale (τ_av) in the Avrami equation have the same activation energy, again equal to the activation energy of viscous flow, which means that in viscous melts (Peclet number <1) the vesiculation (volume expansion), the bubble growth process, and, possibly, the nucleation of vesicles, are controlled by the relaxation of viscous stresses. One of the potential volcanological consequences of such behavior is the existence of a significant time lag between the attainment of a super-saturated state in volatile-bearing rhyolitic magmas and the onset of their expansion. Received: March 20, 1995 / Accepted: October 24, 1995     

An experimental study on semi-brittle and plastic rheology of Panzhihua gabbro

Rheological properties of the crust and upper mantle are essential data that are needed in modelling the mechanical behaviour of the shallow part of the earth. The importance of such data has been seen in discussions about the strength profile of continen…     

Present patterns of decelerating–accelerating seismic strain in South Japan

Decelerating generation of preshocks in a narrow (seismogenic) region and accelerating generation of other preshocks in a broader (critical) region, called decelerating–accelerating seismic strain (D-AS) model has been proposed as appropriate for intermediate-term earthquake prediction. An attempt is made in the present work to identify such seismic strain patterns and estimate the corresponding probably ensuing large mainshocks (M ≥ 7.0) in south Japan (30–38° N, 130–138° E). Two such patterns have been identified and the origin time, magnitude, and epicenter coordinates for each of the two corresponding probably ensuing mainshocks have been estimated. Model uncertainties of predicted quantities are also given to allow an objective forward testing of the efficiency of the model for intermediate-term earthquake prediction.     

Temporal Variability of Lower Stratosphere Temperature

Inter-monthly to inter-decadal global variability of lower stratosphere temperature (LST) is studied in order to improve current knowledge on its variability and trends, as well as natural and anthropogenic influences upon it. Principal Component Analysis (PCA) with S-mode Varimax rotated PCA were used. The first seven components, which explain 70% of variance make it possible to determine homogeneous LST behaviour zones with little overlap between areas, and practically no unclassified areas. Composite time series, referred to as reference series, in the core of the subregions defined by each of the PCs, were calculated in order to obtain the temporal patterns. The equatorial-tropical zone and the subtropical area display warmings caused by the eruptions of El Chichon and Mt. Pinatubo volcanoes as well as the strong influence of the Quasi-Biennial Oscillation (QBO) which leads to equatorial warming (cooling) in the west (east) phase and cooling (warming) in subtropical latitudes. Only low latitudes show some kind of global teleconnection between hemispheres. Significant correlation with several ocean/atmosphere index time-series like ENSO, Antarctic and Arctic Oscillations (AAO, AO), Arctic Circumpolar Vortex was detected over latitudinally separate regions. Antarctic and Arctic ozone hole values were contrasted with warming and cooling features registered in mid and high latitudes in both hemispheres. The LST reference series exhibit a negative trend, commonly attributed to the increase in greenhouse gases that lead to a warming of the troposphere and a cooling of the stratosphere, in all sub regions. The highest cooling rate of − 0.65 °C/ decade is detected in the Gobi desert, and the lowest values of −0.1 °C/ decade over the NE of Canada and Greenland which indicates the great longitudinal variability that the LST trends may present. The difference with other authors is mainly due to the fact that results are based either on latitudinal averages or radiosonde data.     

Surface and Upper Air Fields During Extreme Winter Precipitation Over the Western Himalayas

Surface and upper air circulation features associated with extreme precipitation years are demonstrated during winter season viz., December, January, February and March (DJFM) to examine winter weather affecting the western Himalayas. These circulations are studied over the domain 15°S–45°N and 30°E–120°E. This domain is considered particularly to illustrate the distribution of precipitation due to a wintertime eastward moving synoptic weather system called western disturbances. Surplus and deficient years of seasonal (DJFM) precipitation are identified using ± 20% departure from mean from uninitialized daily reanalysis data of forty (1958–1997) years of the National Center For Environmental Prediction (NCEP), US. The years 1965–1969, 1973 and 1991 are found to be surplus years and the years 1962, 1963, 1971, 1977, and 1985 are found to be deficient years. Comparative study between composites of these two categories is made using students t-test of significance. Significant differences in sea-level pressure, zonal and meridional component of wind at surface and upper levels, total precipitable water content, geopotential height and temperature are observed in the two contrasting seasons.     

Lg Coda Q Variations across South America and their Relation to Crustal Evolution

Nine broadband seismograph stations in South America have provided 389 recordings of Lg coda with paths that cover most of the continent. Lg coda Q (Q0v) and frequency dependence <(eta)> values at 1 Hz, obtained from these records, were inverted using back-projection tomography to obtain regionalized maps of Q0 and <eta>. The entire western margin of the continent (the active Andean mountain belt) is typified by low Q0 (250–450), whereas broad regions of high Q0 (700–1100) span the central Brazilian shield and contiguous regions to the north and south. Intermediate Q0 (450–700) characterizes the northern Patagonia platform and most of the Atlantic shield. Reduced Q0 in the Atlantic shield may be related to tectonic or igneous activity that occurred during the breakup of Gondwanaland during the Jurassic period. This Q distribution is generally consistent with earlier studies where Q0 was found to be directly proportional to the time that has elapsed since the most recent episode of major tectonic or orogenic activity in any region. Reduced Q0 in the Patagonian platform may, however, be due to young sediments there. Q0 is slightly higher in two portions of the Andean belt (between latitudes 2.0°N and 10.0°S, and between latitudes 24.0°S and 34.0°S) than in other portions of the belt. These variations are consistent with results of earlier studies of body-wave attenuation and heat flow in the Andean mountain belt. Spatial variations of <eta> generally vary inversely with Q0v, being low (0.0–0.2) throughout a broad region centered in the central Brazil shield and extending to the northeastern coast. All surrounding regions except that to the northeast exhibit intermediate to high (0.4–0.8 and possibly higher) <eta> values. Possible biasing of Lg coda Q measurements by proximity to the transition between the South American and Pacific plates was examined using records from a station near that boundary and was found to be small.