Eta Model Research Articles

Low Visibility Formation and Forecasting on the Northern Coast of Brazil

Visibility analysis and forecast at the Maceio International Airport in the Brazilian Northeast (NEB) was the principal goal of this investigation. Surface meteorological data of the Maceio International Airport were used for low visibility frequency study. Low visibility in NEB was provoked more frequently by light fog (LF) formation (1,098 or 92 h month−1 on average). Haze and fog were very rare (81 h and one event per year, respectively on average). Light fog with a visibility less than 2 km usually was detected together with rain or drizzle. Low visibility was observed more frequently at night and during the rainy season. Applications of the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model for light fog forecast were tested. Thermodynamic processes were studied by vertical profile, elaborated by: (1) National Centers for Environmental Prediction (NCEP) reanalysis data for Maceio (because of some radiosonde absence) and (2) forecast vertical temperature and humidity profiles were produced, using Air Parcels Trajectories of the HYSPLIT model at the pattern levels. The synoptic situations before and during low visibility phenomena were analyzed using different products of NCEP reanalysis, the high resolution (10 km) ETA model and infrared satellite images. Wave disturbance in the trade winds field, localized on the northwest periphery of the South Atlantic subtropical High, usually accompanied the phenomena. A humidity advection, weak ascendant movement and thermal inversion absence at the low levels were created by these waves. The middle level’s descendent movement provoked the humidity accumulation at levels below. Satisfactory results of the HYSPLIT model applications for light fog forecast were obtained with 12 h antecedence. In particular, stable level forecast by the ETA model was forecast satisfactorily with 12 h antecedence; vertical movements were predicted better with up to 48 h antecedence. The PSU/NCAR mesoscale model (MM5) and PAFOG models were tested for analysis and forecast of an intensive fog event. Intensive fog provoked a fatal accident of a small airplane near the Maceio Airport in 2007. These fog formation processes were studied by NCEP reanalysis data, the high resolution regional model MM5, and satellite and radar data. Fog formation was simulated by PAFOG model and satisfactory results were obtained with 10 h antecedence.

Eta® Analysis of Portfolios: The Economy Matters

The authors introduce a macroeconomic factor model, the Eta model, and its various applications. The underlying message regarding the Eta model, be it for replication, wealth maximization, or wealth preservation, is that “the economy matters.” The core feature of the Eta model is its replication methodology, from which portfolios could be customized to fit the risk–reward preferences of investors with respect to the economy. They then evaluate the portfolios against the Dimensional Fund Advisors Core Equity 1 Portfolio, which adopts the methodology promoted by the Fama–French three-factor model. <b>TOPICS:</b>Factor-based models, portfolio construction, performance measurement

The impact of spring subsurface soil temperature anomaly in the western U.S. on North American summer precipitation: A case study using regional climate model downscaling

This study explores the impact of spring subsurface soil temperature (SUBT) anomaly in the western U.S. on North American summer precipitation, mainly southeastern U.S., and possible mechanisms using a regional climate Eta model and a general circulation model (GCM). The GCM produces the lateral boundary condition (LBC) for the Eta model. Two initial SUBT conditions (one cold and another warm) on May 1st were assigned for the GCM runs and the corresponding Eta runs. The results suggest that antecedent May 1st warm initial SUBT in the western U.S. contributes positive June precipitation over the southern U.S. and less precipitation to the north, consistent with the observed anomalies between a year with a warm spring and a year with a cold spring in the western U.S. The anomalous cyclone induced by the surface heating due to SUBT anomaly propagated eastward through Rossby waves in westerly mean flow. In addition, the steering flow also contributed to the dissipation of perturbation in the northeastern U.S. and its enhancement in southeastern U.S. However, these results were obtained only when the Eta model run was driven by the corresponding GCM run. When the same reanalysis data were applied for both (cold and warm initial SUBT) Eta runs' LBCs, the precipitation anomalies could not be properly produced, indicating the intimate dependence of the regional climate sensitivity downscaling on the imposed global climate forcing, especially when the impact was through wave propagation in the large‐scale atmospheric flow.

Mimicking the standard model Higgs boson in UMSSM

Motivated by the recent results in the standard model (SM) Higgs boson search at the Large Hadron Collider (LHC) we investigate the SM-like CP-even Higgs boson of the U(1)'-extended minimal supersymmetric standard model (UMSSM) and its branching ratio into the b b-bar, W W*, and \chi^0_1 \chi^0_1 modes. In the Summer 2011, a 2 sigma excess was reported in the channel H -> W W* -> l+ nu l- nu-bar around 130 - 140 GeV range. Later on in December 2011 announcements were made that an excess was seen in the 124-126 GeV range, while the SM Higgs boson above 131 GeV up to about 600 GeV is ruled out. We examine two scenarios of these mass ranges: (i) 130 GeV < M_{h_{SM-like}} < 141 GeV and show that the Higgs boson can decay into invisible neutralinos to evade the SM bound; and (ii) 120 GeV < M_{h_{\rm SM-like}} < 130 GeV and show that the Higgs boson can avoid decaying into neutralinos and thus gives enhanced rates into visible particles. We use the \eta model of E_6 with TeV scale supersymmetry to illustrate the idea by scanning the parameter space to realize these two different scenarios.

Seasonal climate hindcasts with Eta model nested in CPTEC coupled ocean–atmosphere general circulation model

This work evaluates the added value of the downscaling technique employed with the Eta model nested in the CPTEC atmospheric general circulation model and in the CPTEC coupled ocean–atmosphere general circulation model (CGCM). The focus is on the austral summer season, December–January–February, with three members each year. Precipitation, latent heat flux, and shortwave radiation flux at the surface hindcast by the models are compared with observational data and model analyses. The global models generally overestimate the precipitation over South America and tropical Atlantic. The CGCM and the nested Eta (Eta + C) both produce a split in the ITCZ precipitation band. The Eta + C produces better precipitation pattern for the studied season. The Eta model reduces the excessive latent heat flux generated by these global models, in particular the Eta + C. Comparison against PIRATA buoys data shows that the Eta + C results in the smallest precipitation and shortwave radiation forecast errors. The Eta + C comparatively best results are though as a consequence of both: the regional model resolution/physics and smaller errors on the lateral boundary conditions provided by the CGCM.

The earthquake magnitude is influenced by previous seismicity

Seismic occurrence is characterized by clustering in space, time and magnitude. Correlations between magnitudes of subsequent events have been recently attributed to catalog incompleteness. Here we investigate the effect of catalog completeness on the amplitude of magnitude correlations. The analysis of two California regions with different levels of catalog accuracy and different lower magnitude thresholds indicate that the amplitude of correlations does not depend on catalog incompleteness. Conversely, correlations are controlled by the probability that two events belong to the same mainshock‐aftershock sequence. Numerical simulations of the ETAS model, where magnitude correlations are absent by construction, provide a counter‐test supporting our conclusions.

An upgraded version of the Eta model

Upgrades implemented over a number of years in an open source version of the Eta model, posted at the CPTEC web site http://etamodel.cptec.inpe.br/ , are summarized and examples of benefits are shown. The version originates from the NCEP’s Workstation Eta code posted on the NCEP web site http://www.emc.ncep.noaa.gov/mmb/wrkstn_eta , which differs from the NCEP’s latest operational Eta by having the WRF-NMM nonhydrostatic option included. Most of the upgrades made resulted from attention paid to less than satisfactory performance noted in several Eta results, and identification of the reasons for the problem. Others came from simple expectation that including a feature that is physically justified but is missing in the code should help. The most notable of the upgrades are the introduction of the so-called sloping steps, or discretized shaved cells topography; piecewise-linear finite-volume vertical advection of dynamic variables; vapor and hydrometeor loading in the hydrostatic equation, and changes aimed at refining the convection schemes available in the Eta. Several other modifications have to do with the calculation of exchange coefficients, conservation in the vertical diffusion, and diagnostic calculation of 10-m winds. Several examples showing improved performance resulting from the dynamics changes are given. One includes a case of unrealistically low temperatures in several mountain basins generated by a centered vertical advection difference scheme’s unphysical advection from below ground, removed by its replacement with a finite-volume scheme. Another is that of increased katabatic winds in the Terra Nova Bay Antarctica region. Successful forecast of the severe downslope zonda wind case in the lee of the highest peaks of the Andes is also shown, and some of the recent successful verification results of the use of the upgraded model are pointed out. The code is used at numerous places, and along with setup information it is available for outside users at the CPTEC Eta web site given above.

Evaluation of Eta Weather Forecast Model over Central Africa

The main goal of this work is to investigate the skills of Eta weather forecast model in forecasting precipitations, temperature and sea level pressure. The model domain extends from 6°W to 29°E and 6°S to 21°N. The model is run with a horizontal resolution of 48 km with 45 vertical levels and initial and boundary conditions were given by National Centers for Environmental Prediction (NCEP) 00UTC operational analysis. All the forecasts are for period of 48 hours. They were compared to the Tropical Rainfall Measuring Mission (TRMM) derived data for precipitations and NCEP/NCAR (National Center for Atmospheric Research) analysis for temperature and sea level pressure. The results show that Eta model predicts fairly good 2 meters temperature and the sea level pressure. Spatial distributions of precipitations are not well simulated by the model.

Can typical households earn hedge fund returns? An analysis of the Eta® replication approach

In this study, we present an extension to the literature on passive hedge fund replication and its applications by introducing the Eta model, and applying it to hedged mutual funds (HMFs) in an attempt to clone their cumulative returns and assessing the skills of fund managers. Although our replication methodology performed reasonably well for HMFs of certain trading strategies, the clones tend to outperform their respective HMFs, which suggest significant managerial influence that compromises fund performance. Finally, with the aid of the Eta model, we constructed a minimum economic risk portfolio, a long-only portfolio comprising exchange traded funds, with quarterly rebalancing, which nevertheless registered higher cumulative returns than funds with access to long/short strategies, leverage and derivatives. This augurs well for a typical household in that it is possible for them to earn hedge fund returns without hedge fund experience or expertise.

Inter event times of fluid induced earthquakes suggest their Poisson nature

[1] We analyze the inter event time distribution of fluid-injection-induced earthquakes for six catalogs collected at geothermal injection sites at Soultz-sous-Forets and Basel. We find that the distribution of waiting times during phases of constant seismicity rate coincides with the exponential distribution of the homogeneous Poisson process (HPP). We analyze the waiting times for the complete event catalogs and find that, as for naturally occurring earthquakes, injection induced earthquakes are distributed according to a non homogeneous Poisson process in time. Moreover, the process of event occurrence in the injection volume domain is a HPP. These results indicate that fluid-injection-induced earthquakes are directly triggered by the loading induced by the fluid injection. We also consider the spatial distance between events and perform a nearest neighbor analysis in the time-space-magnitude domain. Our analysis including a comparison to a synthetic catalog created according to the ETAS model reveals no signs of causal relationships between events. Therefore, coupling effects between events are very weak. The Poisson model seems to be a very good approximation of fluid induced seismicity.

Development and evaluation of a regional ocean-atmosphere coupled model with focus on the western North Pacific summer monsoon simulation: Impacts of different atmospheric components

A regional ocean atmosphere coupled model (ROAM) is developed through coupler OASIS3, and is composed of regional climate model RegCM3 and CREM (Climate version of Regional Eta Model) as its atmospheric component and of a revised Princeton ocean model (POM2000) as its oceanic component. The performance of the ROAM over the western North Pacific summer monsoon region is assessed by the case simulation of warm season in 1998. Impacts of different atmospheric model components on the performance of ROAM are investigated. Compared with stand-alone simulation, CREM (RegCM3) produces more (or less) rainfall over ocean area with inclusion of the air-sea coupling. Different biases of rainfall are caused by the different biases of SST derived from the coupled simulation. Warm (or cold) SST bias simulated by CREM_CPL (RegCM3_CPL) increases (or decreases) the evaporation at sea surface, then increases (or decreases) the rainfall over ocean. The analyses suggest that the biases of vertical profile of temperature and specific humidity in stand-alone simulations may be responsible for the SST biases in regional coupled simulations. Compared with reanalysis data, the warmer (or colder) and moister (or dryer) lower troposphere simulated in CREM (RegCM3) produces less (or more) sea surface latent heat flux. Meanwhile, the more unstable (or stable) lower troposphere produces less (or more) cloudiness at low-level, which increases (or decreases) the solar radiation reaching on the sea surface. CREM (RegCM3) forced by observed SST overestimates (or underestimates) the sea surface net heat flux, implying a potential warm (or cold) heat source. After coupling with POM2000, the warm (or cold) heat source would further increase (or decrease) the SST. The biases of vertical profile of temperature and specific humidity may be ascribed to the different representation of cumulus convection in atmospheric models. inter-comparison of regional coupling, different atmospheric component, western North Pacific summer monsoon, model biases

Earthquake precursors: activation or quiescence?

SUMMARY We discuss the long-standing question of whether the probability for large earthquake occurrence (magnitudes m > 6.0) is highest during time periods of smaller event activation, or highest during time periods of smaller event quiescence. The physics of the activation model are based on an idea from the theory of nucleation, that a small magnitude earthquake has a finite probability of growing into a large earthquake. The physics of the quiescence model is based on the idea that the occurrence of smaller earthquakes (here considered as magnitudes m > 3.5) may be due to a mechanism such as critical slowing down, in which fluctuations in systems with long-range interactions tend to be suppressed prior to large nucleation events. To illuminate this question, we construct two end-member forecast models illustrating, respectively, activation and quiescence. The activation model assumes only that activation can occur, either via aftershock nucleation or triggering, but expresses no choice as to which mechanism is preferred. Both of these models are in fact a means of filtering the seismicity time-series to compute probabilities. Using 25 yr of data from the California–Nevada catalogue of earthquakes, we show that of the two models, activation and quiescence, the latter appears to be the better model, as judged by backtesting (by a slight but not significant margin). We then examine simulation data from a topologically realistic earthquake model for California seismicity, Virtual California. This model includes not only earthquakes produced from increases in stress on the fault system, but also background and off-fault seismicity produced by a BASS–ETAS driving mechanism. Applying the activation and quiescence forecast models to the simulated data, we come to the opposite conclusion. Here, the activation forecast model is preferred to the quiescence model, presumably due to the fact that the BASS component of the model is essentially a model for activated seismicity. These results lead to the (weak) conclusion that California seismicity may be characterized more by quiescence than by activation, and that BASS–ETAS models may not be robustly applicable to the real data.

A modeling study of an Antarctica polynya event

An event of polynya at Terra Nova Bay (TNB), occurring from 15 July to 17 July 2006, is simulated by a recent version of the mesoscale Eta model. Simulation results and observational data describe the surface conditions during the period. The spatial and temporal structure of the atmospheric boundary layer in response to the warm area of the polynya is also investigated. Numerical experiments show that the latter influences significantly the wind intensity, the temperature and the specific humidity of the air over Terra Nova Bay. The significant heating of the low atmosphere results in a three-dimensional anomaly in the baric field, which extends far in the Ross Sea, embedded in the complex pressure field obtained by the Eta model also without taking into account the polynya. A turbulent kinetic energy plume, indicating turbulent mixing, and an increased vertical diffusion of horizontal momentum are also simulated over the polynya. The downward flux of high momentum air and the modified pressure gradient force change the wind speed at low level over TNB.

Evaluation of soil moisture from satellite observations over South America

A study was performed to evaluate the surface soil moisture derived from Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) sensor observations over South America. Other soil moisture and rainfall datasets were also used for the analysis. The information for the soil data came from the Eta regional climate model, and for the rainfall data from the Tropical Rainfall Microwave Mission (TRMM) satellite. Statistical analysis was used to evaluate the quality of the soil moisture and rainfall products, with estimates of the correlation coefficient (R), χ2 and Cramer's phi (ϕc). The results show high correlations (R > 0.8) of the AMSR-E soil moisture products with the Eta model for different regions of South America. Comparison of soil moisture products with rainfall datasets showed that the AMSR-E C-band soil moisture product was highly correlated with the TRMM satellite rainfall datasets, with the highest values of χ2 and ϕ. The results show that the AMSR-E C-band soil moisture products contain important information that can be used for various purposes, such as monitoring floods or droughts in arid areas or as input within the framework of an assimilation scheme of numerical weather prediction models.

On the change of the tropical cyclone structure during its passage over islands

The impact is studied of small land areas on the configuration and structure of the tropical cyclone as well as on the variations of different characteristics of hurricanes (wind field, kinetic energy, and vorticity) during their passage over islands. The results of computations based on the regional numerical atmospheric ETA model for the hurricanes of the Caribbean Sea and typhoons of the Northwestern Pacific revealed that the disturbance of the symmetric circulation in the vortex accompanied by significant kinetic energy losses takes place when crossing the archipelagos or separate islands. It is demonstrated that the vortex intensity depends not on the energy loss due to the underlying surface roughness only but on the heat flux from it as well. The kinetic energy generation in the hurricane sharply decreases as a result of the decrease in the pressure gradient over the land that is caused, in turn, by the tropical cyclone moving away from the oceanic heat source. At the recurring appearance of the cyclone over the warm ocean waters, its deepening and intensification recommence.

Case Studies of Easterly Wave Disturbances over Northeast Brazil Using the Eta Model

Abstract This research aims to analyze two easterly wave disturbance events that reached the east coast of Northeast Brazil (NEB) on 15 May 2005 and 20 June 2006. The performance of the regional Eta Model was evaluated through four sets of experiments using different horizontal resolutions (10 and 40 km) and convective parameterization schemes [Betts–Miller–Janjić (BMJ) and Kain–Fritsch (KF)]. Through analysis of 700-hPa wind fields, all experiments, with 40- and 10-km horizontal resolutions and using the BMJ and KF schemes, were shown to well represent a trough propagating westward from about 20°W to NEB, with a 5-day forecast range. When evaluating the model sensitivity to different convective parameterizations, all the experiments showed similar results and underestimated rainfall in most of the domain. The obtained results suggest the need to extend this analysis to a larger number of cases and to test other cumulus parameterizations in order to improve the rainfall forecast in eastern NEB.

Rare events of stratus clouds on the northeast coast of Brazil

One event of three consecutive days and another of four consecutive days of Stratus clouds were registered at the Maceio airport on the northeast coast of Brazil. This is a very rare phenomenon for equatorial regions and it was analyzed using the high resolution (10km) ETA model, NCEP reanalysis, satellite data and conventional data supplied by the Hydrometeorological Directory DHM-SERHI/AL and by the Department of Flight Protection of the Zumbi dos Palmares airport. Wave disturbance in the trade winds and weak ascendant movements at low levels (1000 and 925hPa) were identified. At the same time, anticyclonic curvature at high levels formed descendant movements and subsidence inversion. These vertical movements combined with a stable layer between 850 and 700hPa created a very humid layer at the low levels. The precipitation forecasted by the ETA model with 24h antecedence presented a satisfactory result for an average quantity of precipitation. Nevertheless, the spatial distributions of forecasted and observed precipitation were different. Precipitation during all days was not forecasted for the coastal region, and for the west region the forecasted precipitation was more intense than the observed ones.

Downscaling of South America present climate driven by 4-member HadCM3 runs

The objective of this work is to evaluate climate simulations over South America using the regional Eta Model driven by four members of an ensemble of the UK Met Office Hadley Centre HadCM3 global model. The Eta Model has been modified with the purpose of performing long-term decadal integrations and has shown to reproduce “present climate”—the period 1961–1990—reasonably well when forced by HadCM3. The global model lateral conditions with a resolution of 2.5° latitude × 3.75° longitude were provided at a frequency of 6 h. Each member of the global model ensemble has a different climate sensitivity, and the four members were selected to span the range of uncertainty encompassed by the ensemble. The Eta Model nested in the HadCM3 global model was configured with 40-km horizontal resolution and 38 layers in the vertical. No large-scale internal nudging was applied. Results are shown for austral summer and winter at present climate defined as 1961–90. The upper and low-level circulation patterns produced by the Eta-CPTEC/HadCM3 experiment set-up show good agreement with reanalysis data and the mean precipitation and temperature with CRU observation data. The spread in the downscaled mean precipitation and temperature is small when compared against model errors. On the other hand, the benefits in using an ensemble is clear in the improved representation of the seasonal cycle by the ensemble mean over any one realization. El Nino and La Nina years were identified in the HadCM3 member runs based on the NOAA Climate Prediction Center criterion of sea surface temperature anomalies in the Nino 3.4 area. The frequency of the El Nino and La Nina events in the studied period is underestimated by HadCM3. The precipitation and temperature anomalies typical of these events are reproduced by most of the Eta-CPTEC/HadCM3 ensemble, although small displacements of the positions of the anomalies occur. This experiment configuration is the first step on the implementation of Eta-CPTEC/HadCM3 upcoming experiments on climate change studies that are discussed in a companion paper.

Detection of Fluid Signals in the 1985 Yellowstone Earthquake Swarm

This paper presents a statistical approach named multivariate hidden Markov modeling (MHMM) and employs it to study the spatial and temporal distribution of earthquakes in the 1985 Yellowstone earthquake swarm. It also explores the potential of the approach for identifying fluid signals in the swarm. As far as the spatial distribution component is concerned, the MHMM detected an upward migration of earthquakes at the beginning of the swarm. This is an important feature of fluid-triggered earthquakes. In terms of the temporal distribution component, the agreement between the MHMM and ETAS modeling results suggests the presence of fluid signals in mid-November of 1985.

A Four-Dimensional Variational Data Assimilation Approach with Analysis at the End of Assimilation Window. Part I: Methodology and Preliminary Tests

In this paper, we propose a new approach to four-dimensional variational data assimilation (4DVar) with analysis of the initial condition (IC) at the end of assimilation window. The new approach is referred to as “backward 4DVar (B-4DVar).” The minimization of its cost function is fulfilled through an ensemble of historical prediction samples. B-4DVar is computationally efficient because it does not use tangent linear or adjoint models. To prepare it for numerical weather prediction, a B-4DVar assimilation system is developed based on an operational regional prediction model, the Advanced Regional Eta Model (AREM). Two single observation experiments (SOEs) and an observing system simulation experiment (OSSE) are conducted to evaluate the system. The SOEs reveal a characteristic of flow dependence in B-4DVar, which is consistent with statistical estimation of the background error covariance matrix (simply B-matrix) using a group of IC-reliant historical prediction samples. The OSSE suggests that the B-4DVar approach improves the analytic quality of IC by effectively incorporating conventional observations, thereby outperforming the 3DVar. The time-saving feature, flow dependence in B-matrix, and good performance in assimilating conventional observations indicate the potential and feasibility of B-4DVar in operational use.