Assessment of global ionospheric maps performance in the Brazilian region using ionosonde data

<p>In this work, we present a new method for assessing global ionospheric maps (GIM) by means of ionosonde data. The method proposed is based on the critical frequency at the F<sub>2</sub> layer directly measured by pairs of ionosondes to assess VTEC (vertical total electron content) values from GIMs. Four strategies were investigated and, the best one was the linear interpolation of squared f<sub>o</sub>F<sub>2</sub> based on the VTEC ratio. The analysis was based on the root mean square (RMS) of the differences between the measured and estimated f<sub>o</sub>F<sub>2</sub> values at the first ionosonde from each pair. The f<sub>o</sub>F<sub>2</sub> were estimated using the values measured at the second ionosonde and interpolated to the position of the first ionosonde with the VTEC values from the GIMs. Besides the RMS values, additional ionospheric indicators (slab thickness and shape function peak) were used to complement the daily analysis. This method was tested over one of the most challenging scenarios, the Brazilian region and near the last solar cycle peak. The assessment considered four ionosondes (combined in six pairs) and thirteen GIM products available at CDDIS (Crustal Dynamics Data Information System), CORG, CODG, EHRG, ESRG, ESAG, IGRG, IGSG, JPLG, UPRG, UPCG, UQRG, WHRG and WHUG. Analysis was conducted using daily, weekly, one year, and four years of data. The analysis with daily data showed that slab thickness and shape function peak could be helpful to identify periods and regions where this method could be applied. The weekly analysis was performed to select the best strategy to interpolate the f<sub>o</sub>F<sub>2</sub> values. The analysis of one-year data (2015) was performed considering all GIMs previously mentioned. CODG, IGSG, JPLG, UQRG, WHRG, and WHUG provided the best results, with mean rates of improvement up to 42% in comparison to not using any GIM. The four-year time series (2014-2017) were analyzed considering the two products with better performance for the one-year analysis (CODG and UQRG). With data from 2014-2017, CODG and UQRG provided improvement rates of up to 49%. In general, regional and temporal ionospheric influences could be noticed in the results, with expected larger errors closer to the solar cycle peak in 2014 and at locations with pairs of ionosondes with the larger distance apart. Therefore, we have confirmed the viability of the developed approach as an assessment method to analyze GIMs quality based on ionosonde data.</p>

Assessment of Global Ionospheric Maps Performance by Means of Ionosonde Data

This work presents a new method for assessing global ionospheric maps (GIM) using ionosonde data. The method is based on the critical frequency at the F2 layer directly measured by ionosondes to validate VTEC (vertical total electron content) values from GIMs. The analysis considered four different approaches to using foF2. The study was performed over one of the most challenging scenarios, the Brazilian region, considering four ionosondes (combined in six pairs) and thirteen GIM products available at CDDIS (Crustal Dynamics Data Information System). Analysis was conducted using daily, weekly, one year (2015), and four years (2014–2017) of data. Additional information from the ionosphere was estimated to complement the daily analysis, such as slab thickness and shape function peak. Results indicated that slab thickness and shape function peak could be used as alternative indicators of periods and regions where this method could be applied. The weekly analysis indicated the squared frequency ratio with local time correction as the best approach of using foF2, between the ones evaluated. The analysis of one-year data (2015) was performed considering thirteen GIMs, where CODG and UQRG were the two GIMs that presented the best performance. The four-year time series (2014–2017) were analyzed considering these two products. Regional and temporal ionospheric influences could be noticed in the results, with expected larger errors during the solar cycle peak in 2014 and at locations with pairs of ionosondes with the larger distance apart. Therefore, we have confirmed the viability of the developed approach as an assessment method to analyze GIMs quality based on ionosonde data.

Dynamic Channel Selection of Microwave Temperature Sounding Channels under Cloudy Conditions

To make better use of microwave radiance observations for data assimilation, removal of radiances contaminated by hydrometeor particles is one of the most important steps. Generally, all observations below the middle troposphere are eliminated before the analysis when precipitation is present. However, the altitude of the cloud top varies; when the weighting function peak height of a channel is higher than the altitude of the cloud top, observations are not affected by the absorption or scattering of cloud particles. Thus, the radiative transfer calculation can be performed under a clear sky scenario. In this paper, a dynamic channel selection (DCS) method was developed to determine the radiance observations unaffected by clouds under cloudy conditions in assimilation. First, the sensitivity of cloud liquid water (CLW) profiles to radiance from the microwave temperature sounding frequencies was analyzed. It was found that the impact of CLW on transmittance can be neglected where the cloud top height is below the weighting function peak height. Second, three lookup tables were devised through analysis of the impact of cloud fraction and cloud top height on radiance, which is the basis of the DCS method. The unified cloud top height of the Microwave Temperature Sounder (MWTS)-2 fields of view (FOVs) can be calculated by remapping the cloud mask and cloud top height data from the Medium Resolution Spectral Imager-2 (MERSI-2). Observations from various channels may be removed or retained based on real-time dynamic unified cloud top height data. Twelve-hour and long-term time-series brightness temperature simulation experiments both showed that an increase in the amount of observations used for data assimilation of more than 300% can be achieved by application of DCS, but this had no effect on the amount of error. Through DCS, areas of strong precipitation can be accurately identified and removed, and more observations above cloud top height can be included in the data assimilation. The application of DCS to data assimilation will greatly improve the data utilization rate, and therefore allow for more accurate characterization of upper atmospheric circulation.

Physical Function in U.S. Older Adults Compared With Other Populations: A Multinational Study

Objective: We compare physical performance from three U.S. national surveys and nationally representative surveys in England, Taiwan, and Costa Rica. Method: For each performance test, we use local mean smoothing to plot the age profiles by sex and survey wave and then fit a linear regression model to the pooled data, separately by sex, to test for significant differences across surveys controlling for age and height. Results: Age profiles of performance vary across U.S. surveys, but levels of lung function (peak expiratory flow) and handgrip strength in the United States are as high as they are in the other three countries. Americans also perform as well on the chair stand test as the English and Costa Ricans, if not better, but exhibit slower gait speed than the English at most ages. Discussion: With the exception of walking speed, we find little evidence that older Americans have worse physical performance than their peers.

Basic Methods of Peak-Hour Traffic Generation Forecast about Urban Commercial Complex

Based on analysis of the traffic impacts characteristics of the urban commercial complex, the article proposed that single-functional project itself generated traffic volume is related to time, and conforms to the corresponding Poisson distribution function. However, the multiple-functional complex itself generated peak-hour traffic volume is not a simple sum of each single-function peak volume, but is calculated by superposing the each function respective traffic density functions. Meanwhile, the article also explored the superposition and calculation method to obtain peak-hour traffic volume during forecasting the trip generation of the urban commercial complex.

Research on Computer Controlled Optical Surfacing (CCOS) Working Function at Wear State

The distribution of working pressure in CCOS has been studied when the polishing disc frayed. Combined with the planetary motion, the working functions at wear and ideal states were calculated separately, the result shows that the function peak is higher at wear state and it is a convex curve instead of a concave curve at ideal state. The impact of different wear loss on the working function has been also studied in this paper, one preliminary conclusion has been obtained that with the increasing of the wear loss, the working function peak will get higher and sharper, and the effective range of processing will decrease meanwhile. It can be predicted that although the removal rate may not change obviously at the initial stage of wear, the processing quality may decrease and the processing stability will be worse since the variation of the removal distribution.