18,585 research outputs found
Investigating the Kinematics of Coronal Mass Ejections with the Automated CORIMP Catalog
Studying coronal mass ejections (CMEs) in coronagraph data can be challenging
due to their diffuse structure and transient nature, compounded by the
variations in their dynamics, morphology, and frequency of occurrence. The
large amounts of data available from missions like the Solar and Heliospheric
Observatory (SOHO) make manual cataloging of CMEs tedious and prone to human
error, and so a robust method of detection and analysis is required and often
preferred. A new coronal image processing catalog called CORIMP has been
developed in an effort to achieve this, through the implementation of a dynamic
background separation technique and multiscale edge detection. These algorithms
together isolate and characterise CME structure in the field-of-view of the
Large Angle Spectrometric Coronagraph (LASCO) onboard SOHO. CORIMP also applies
a Savitzky-Golay filter, along with quadratic and linear fits, to the
height-time measurements for better revealing the true CME speed and
acceleration profiles across the plane-of-sky. Here we present a sample of new
results from the CORIMP CME catalog, and directly compare them with the other
automated catalogs of Computer Aided CME Tracking (CACTus) and Solar Eruptive
Events Detection System (SEEDS), as well as the manual CME catalog at the
Coordinated Data Analysis Workshop (CDAW) Data Center and a previously
published study of the sample events. We further investigate a form of
unsupervised machine learning by using a k-means clustering algorithm to
distinguish detections of multiple CMEs that occur close together in space and
time. While challenges still exist, this investigation and comparison of
results demonstrates the reliability and robustness of the CORIMP catalog,
proving its effectiveness at detecting and tracking CMEs throughout the LASCO
dataset.Comment: 23 pages, 11 figures, 1 tabl
Understanding decreases in land relative humidity with global warming: conceptual model and GCM simulations
Climate models simulate a strong land-ocean contrast in the response of
near-surface relative humidity to global warming: relative humidity tends to
increase slightly over oceans but decrease substantially over land. Surface
energy balance arguments have been used to understand the response over ocean
but are difficult to apply over more complex land surfaces. Here, a conceptual
box model is introduced, involving moisture transport between the land and
ocean boundary layers and evapotranspiration, to investigate the decreases in
land relative humidity as the climate warms. The box model is applied to
idealized and full-complexity (CMIP5) general circulation model simulations,
and it is found to capture many of the features of the simulated changes in
land relative humidity. The box model suggests there is a strong link between
fractional changes in specific humidity over land and ocean, and the greater
warming over land than ocean then implies a decrease in land relative humidity.
Evapotranspiration is of secondary importance for the increase in specific
humidity over land, but it matters more for the decrease in relative humidity.
Further analysis shows there is a strong feedback between changes in
surface-air temperature and relative humidity, and this can amplify the
influence on relative humidity of factors such as stomatal conductance and soil
moisture.Comment: Submitted to Journal of Climate on May 1st, 201
Unit Roots and Structural Breaks: A Survey of the Literature
Since Perron (1989) the time series literature has emphasised the importance of testing for structural breaks in typical economic data sets and pronounced the implications of structural breaks when testing for unit root processes. In this paper we survey recent developments in testing for unit roots taking account of possible structural breaks. In doing so we discuss the distinction between taking structural break dates as exogenously determined, an approach initially adopted in the literature, and endogenously testing break dates. That is, we differentiate between testing for breaks when the break date is known and when it is assumed to be unknown. Also important is the distinction between discrete breaks and gradual breaks. Additionally we describe tests for both single and multiple breaks and discuss some of the pitfalls of the latter.
Common factors of the exchange risk premium in emerging European markets
Existing empirical evidence suggests that the Uncovered Interest Rate Parity (UIRP) condition may not hold due to an exchange risk premium. For a panel data set of eleven emerging European economies we decompose this exchange risk premium into an idiosyncratic (country-specific) element and a common factor using a principal components approach. We present evidence of stationary idiosyncratic and common factors. This result leads to the conclusion of a stationary risk premium for these countries, which is consistent with previous studies often documenting a stationary premium in developed countries. Furthermore, we report that the variation in the premium is largely attributable to a common factor influenced by economic developments in the United States.Uncovered Interest Rate Parity, Emerging Economies, Exchange Risk Premiums, Common Factors
Structural Breaks in the Real Exchange Rate and Real Interest Rate Relationship
In this paper we empirically examine the relationship between the real exchange rate and real interest rate differentials using recent econometric methods robust to potential structural breaks. Generally, our study provides evidence of this relationship in the long-run context. More specifically, we first focus on the UK-US relationship, and interestingly find limited evidence of this long-run relationship using traditional methods. But when an approach robust to endogenously determined structural breaks is employed, we find evidence that the real interest rate differential is an important determinant of the real exchange rate. Secondly, in order to investigate the relevance of structural shifts in a more global context, we carry out multiple country analysis. While providing evidence of this long-run relationship, European data suggest that the presence of structural breaks is not very common across countries and is indeed country-specific.Real exchange rate; real interest rate differential; nonstationarity; endogenously determined structural breaks; trace tests
Euro Area Inflation: Aggregation Bias and Convergence
EMU monetary policy targets aggregate Euro Area inflation. Concerns are growing that a focus on aggregate inflation may cause national inflation rates to diverge. While different explanations for diverging aggregate Euro Area inflation have been brought forward, the very impact of aggregation on divergence has however not been studied. We find a striking difference in convergence depending on the level of aggregation. While aggregate national inflation rates are diverging, disaggregate inflation rates are converging. We find that aggregation appears to bias evidence towards non-convergence. Our results are consistent with prominent theoretical and empirical evidence on aggregation biasEuro Area Inflation; Aggregation Bias; Convergence
International capital flows to emerging and developing countries: national and global determinants
This paper examines international capital flows to emerging and developing countries. We assess whether commonalities exist, the permanence of shocks to commonalities and their determinants. Also, we consider individual country coherence with global capital flows and we measure the extent of co-movements in the volatility of capital flows. Our results suggest there are commonalities in capital inflows, although aggregate or disaggregate capital flows respond differently to shocks. We find that the US long run real interest rate is an important determinant of global capital flows, and real commodity prices are relevant but to a lesser extent. We also find a role for human capital in explaining why some countries can successfully ride the wave of financial globalisation.Capital Flows; Emerging Markets; Developing Countries; Global Factors
Supporting development for the preliminary design of an intermediate water recovery system
Supporting development of experimental design for water recovery syste
Common and idiosyncratic factors of the exchange risk premium in emerging European markets
Existing empirical evidence suggests that the Uncovered Interest Rate Parity (UIRP) condition may not hold due to an exchange risk premium. For a panel data set of eleven emerging European economies we decompose this exchange risk premium into an idiosyncratic (country-specific) elements and a common factor using a principal components approach. We present evidence of a stationary idiosyncratic component and nonstationary common factor. This result leads to the conclusion of a nonstationary risk premium for these countries and a violation of the UIRP in the long-run, which is in contrast to previous studies often documenting a stationary premium in developed countries. Furthermore, we report that the variation in the premium is largely attributable to a common factor influenced by economic developments in the United States.Uncovered Interest Rate Parity, Emerging Economies, Exchange Risk Premiums, Common Factors
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