ALBERT

Description: ABSTRACT A 175 years long homogenized composite record of monthly mean temperatures is presented for Oslo, the capital of Norway. The early raw data have been digitised and quality controlled, and monthly means have been calculated. Some early original observations carried out in a Wild screen (1877–1936) were found to be spuriously high because of inappropriate sheltering from sunlight. These spurious temperatures were not used in the composite record, but alternative temperatures measured (1837–1933) by thermometers placed outside windows at the Astronomical Observatory were used instead. No inhomogeneity was detected in the latter series after adding an instrument correction of +0.3 °C, but the start year of the correction remains uncertain. The more recent part of the composite record used the long-term series (1937 to present) from Blindern in Oslo, the premises of The Norwegian Meteorological Institute. Two small inhomogeneities were detected in the Blindern series, possibly caused by a weak urban heat island effect or growing/cutting of trees. The study revealed that the annual mean temperature has increased by 1.5 °C in the period 1838–2012. The most pronounced increase in annual temperature occurred during the last 50 years, and in the early 20th century that ended with a local maximum in the 1930s. The temperature has increased significantly in all seasons; however, the temperature increase in summer was less than a half of that in winter and spring, which were the seasons with largest increase. In addition the monthly mean temperature of the coldest month in each year has increased two times faster than the warmest one. The most significant temperature variations were associated to ∼ 5-year time scales in its early part, but since 1930 and up to present, the dominant time scales were 10–20 years.

Description: No abstract is available for this article.

Description: A new permanent ELF measurement station has been deployed in Sierra Nevada, Spain. It is composed of two magnetometers, oriented NS and EW, respectively. At 10 Hz, their sensitivity is 19 μ zV/pT and the Signal to Noise Ratio (SNR) is 28 dB for a time-varying signal of 1 pT, the expected field amplitude in Sierra Nevada. The station operates for frequencies below 24 Hz. The magnetometers, together with their corresponding electronics, have been specifically designed to achieve such an SNR for small signals. They are based on high-resolution search coils with ferromagnetic core and 10 6 turns, operating in limited geometry configuration. Different system noise sources are considered and a study of the SNR is also included. Finally, some initial Schumann resonance measurements are presented in order to validate the performance of the measurement station, including one hour length spectra, daily variations of resonance amplitudes and frequencies for the different seasons, and a three day spectrogram.

Description: ABSTRACT The onset, retreat and the length of growing season in the north-eastern region of Sri Lanka were investigated using daily rainfall data for the period 1961 to 2000. Data from three weather stations situated in the coastal belt in the northern and eastern parts of Sri Lanka (Jaffna, Trincomalee and Batticaloa) that receive rainfall predominantly from the northeast monsoon were selected for this study. A method based on cumulative rainy days was utilized in the determination of the onset and retreat dates. It is shown that there is substantial interannual variability in onset and retreat dates. The mean onset and retreat dates fall on the standard week 38.3 ± 2.7 and 53.0 ± 2.9, respectively. The mean duration of the growing season is 14.7 ± 3.4 weeks. The retreat date and thus the length of growing season could be extended by 2 weeks if the probability of occurrence of rain during the onset is favourable for the retreat. The results indicate that there has been no significant trend in the onset and retreat dates during the last 40 years in the dry zone of Sri Lanka. The onset date and the length of growing season are weakly correlated with early onset dates leading to longer growing seasons. The study concludes that rainy days could be used successfully to determine the mean rainfall onset and retreat dates in the dry zone of Sri Lanka.

Description: ABSTRACT A 256-year composite monthly rainfall record representative of the lowlands around Carlisle, northwest England is presented, providing the third longest instrumental record of rainfall available in the UK and expanding the sparse network of long homogenous rainfall series. This article describes the construction of the rainfall record for the period 1757–2012 and presents analyses of long-term annual and seasonal variability, with a particular focus on wet/dry extremes. Three primary rainfall records from Carlisle underpin the reconstruction, with others selected based on length of record and proximity to the primary recording stations. Linear regression and adjustment factors were applied to create a homogenous continuous rainfall record, assessed by cross-comparison with other long-term UK rainfall records. Double-mass curve and standard normal homogeneity tests using long records representative of Manchester and Appleby confirmed that the Carlisle record is homogenous, but includes a period of uncertainty during the period 1886–1911, which is within the recognized instrumental phase of recording. Analysis of the series shows long-term temporal rainfall variability, with seasonal rainfall totals showing a significant increase in winter rainfall. An increasing trend in annual rainfall was also identified but is not significant. Several previously documented notable extreme wet (e.g. winter 1834) and dry (e.g. summer 1995) seasons were identified, along with several additional seasons (e.g. winter 1764 and summer 1891) that can be considered as extreme and occurred during the more poorly understood 18th and early 19th centuries. These results allow recent extremes to be placed within the context of long-term natural variability. At the decadal timescale seasonal rainfall totals are highly variable. The wettest season fluctuates between autumn and summer until the late 20th century (1990s), when winter became wetter than any other season for the first time on record.

Description: ABSTRACT Policymakers, governments and aid agencies require operational environmental monitoring in support of evidence-based policy-making and resource deployment in crisis situations. For Africa, this is only feasible at sub-continental scale with a large network of automated meteorological stations, a large number of highly coordinated field observers or with satellite remote sensing. The challenge with satellite data lies in the derivation of meaningful environmental indicators. This article describes a conceptual framework for understanding satellite-derived indicators of rainfall and vegetation greenness trends over Africa. It attributes observed vegetation changes to climatic (i.e. rainfall linked) and non-climatic drivers. A decade of annual rainfall and vegetation data over sub-Saharan Africa was analysed using satellite-based rainfall estimates [Famine Early Warning System Rainfall Estimation 2.0 (FEWSNET RFE 2.0)] from National Oceanic and Atmospheric Administration's (NOAA's) Climate Prediction Centre and the Normalized Difference Vegetation Index (NDVI) obtained from the Satellite Pour l'Observation de la Terre Vegetation (SPOT-VGT) sensor. Rainfall and vegetation greenness trends were analysed for 759 administrative regions of sub-Saharan Africa to identify those regions that have experienced a negative, positive or stable rainfall/vegetation trend over the period 2001–2010. The character of the relationship between the annual rainfall and max NDVI trends were examined to identify areas where the changes in greenness could be attributed to climatic (rainfall) and non-climatic (human land use or ecological disturbance) changes. Regions where increasing rainfall was associated with vegetation greening were found in West Africa, Central African Republic, West Cameroon and northeastern part of South Africa, whereas areas with evidence of ‘climatic vegetation degradation’ were located in Southern Madagascar, Nigeria, Kenya and the Garden Route region of South Africa.

Description: ABSTRACT The North African climate is analysed for August during a 32-year period using the European Centre for Medium Range Weather Forecast (ECMWF) global data set to investigate the intensity variability at 600 mb of the subtropical highs, Africa easterly jet (AEJ) with two embedded local wind maxima, and African easterly waves over North Africa and the Arabian Peninsula. The variability of these synoptic weather systems is higher in East Africa. The most noticeable variability of intensity occurred with easterly waves. Maintenance of easterly waves from the Arabian Peninsula into East Africa is dependent on strong zonal gradients from the AEJ through shear vorticity. These zonal gradients were induced by the strengthening of the subtropical highs and the presence of a westerly jet in Central Africa and south of the Arabian Peninsula. During positive ENSO periods, these systems are generally weaker while in negative periods are stronger. The focus of this research is to investigate the role of the Arabian High and eastern local wind maximum (LWM E ) on complementing the Saharan High and western local wind maximum (LWM W ). It is found that an intense local wind maximum in East Africa helps maintain the easterly waves and their westward propagation from the Arabian Peninsula.

Description: Electromagnetic inspection techniques are becoming powerful tools for buried object detection and subsurface prospection in several applicative fields, such as civil engineering and archeology. However, the nonlinearity and ill-posedness of the underlying inverse problem make the development of efficient imaging techniques a very challenging task. In the present paper, an algorithm based on a regularizing approach in L p Banach spaces is proposed for tackling such problems. The effectiveness of the approach is verified by means of numerical simulations in a noisy environment, aimed at evaluating the reconstruction capabilities with respect to the choice of several model parameters. The reported results show that, for small targets, the use of L p Banach spaces with 1 〈  p  〈 2 allows to obtain a better localization of different buried scatterers.

Description: Using numerical simulations, we investigated a method for calculating the spectral parameters from Doppler spectra collected by high-resolution wind profiler radars (WPRs). Because high-resolution WPRs collect a huge amount of Doppler spectra, calculations must be simple and fast. The proposed method has two steps. In the first step, the echo range ( R echo ), in which the Doppler spectrum point with peak intensity is contained and all the smoothed Doppler spectrum points have intensities that are greater than the noise intensity, was determined. For producing the smoothed Doppler spectrum, a running average with equal weight (RA) or multi-taper method (MTM) was used. In the second step, the spectral parameters were calculated using the Doppler spectrum points within R echo . By comparing the performance of the computation methods using RA and MTM, we concluded that the computation method using RA is more suitable because it has better estimation performance for small spectrum widths and the calculations are faster. Estimation error of the spectral parameters depends on the determination accuracy of the Doppler spectrum peak and R echo . Furthermore, for the case of a 512-point Doppler spectrum and 13-point RA, the estimation errors tend to be independent of the signal-to-noise ratio (SNR) when the peak level of the Doppler spectrum ( p est ) is ~8 dB or more greater than the noise intensity. For p est of 〈 ~8 dB, the estimation errors are well correlated to p est and the SNR. Therefore, the number of incoherent integration times should be determined by considering the SNR and p est .

Description: Ionospheric total electron content (TEC) and atmospheric density perturbations were derived from measurements made from instruments onboard the Gravity Recovery and Climate Experiment (GRACE) spacecraft. At the time of the Tohoku-Oki earthquake on March 11, 2011, the twin spacecraft were orbiting at an altitude of ~450 km over Alaska. Significant TEC fluctuations (up to 0.6 TEC units), atmospheric density perturbations (~3.6 · 10 −14  kg/m 3 ), and sudden changes in GRACE acceleration (~4 · 10 −8  m/s 2 ) were observed ~8 minutes after the arrival of seismic and infrasound waves on the ground in Alaska, ~20 minutes after the Tohoku-Oki main shock at 05:46:23 UTC. The results of three-dimensional ionospheric-thermospheric modeling and infrasound ray-tracing simulations are consistent with the arrival time and physical characteristics of the disturbances at GRACE. This is the first time that ionospheric disturbances associated with an earthquake are clearly attributable to perturbations at such high altitudes.