Jiuhou Lei

Bio: Jiuhou Lei is an academic researcher from University of Science and Technology of China. The author has contributed to research in topics: Ionosphere & Thermosphere. The author has an hindex of 43, co-authored 235 publications receiving 5465 citations. Previous affiliations of Jiuhou Lei include University of Colorado Boulder & Chinese Academy of Sciences.

Comparison of COSMIC ionospheric measurements with ground-based observations and model predictions : Preliminary results

Abstract: [1] Electron densities retrieved from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) measurements are compared with those measured by incoherent scatter radars (ISR) and ionosondes in this paper. These results show that electron density profiles retrieved from COSMIC RO data are in agreement with the ISR and ionosonde measurements. The ionospheric characteristics (NmF2 and hmF2) derived from the COSMIC satellites are also compared with those calculated by the latest International Reference Ionosphere model (IRI-2001) and the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (NCAR-TIEGCM). The comparison of the magnitude of the COSMIC NmF2 data with those calculated by the IRI model and the TIEGCM is good. However, features such as the north-south asymmetry and longitudinal variation of the equatorial anomaly that are seen in the COSMIC data and the TIEGCM simulations are not fully present in the IRI model. On the other hand, the TIEGCM produces a stronger winter anomaly than that seen in either the COSMIC data or the IRI model.

Is an unusual large enhancement of ionospheric electron density linked with the 2008 great Wenchuan earthquake

Abstract: [1] On 12 May 2008 at 0628 UT a major earthquake Ms = 8.0 struck Wenchuan County (31.0°N, 103.4°E) in southwest China. The maximum ionospheric electron density at F2 peak (NmF2) recorded an unusual large enhancement during the afternoon-sunset sector by the Chinese ionosondes over Wuhan (30.5°N, 114.4°E) and Xiamen (24.4°N, 123.9°E), which are close to the earthquake epicenter. An averaged increase at these two stations is about 2 times on a geomagnetic quiet day, 9 May (Kp ≤ 2), 3 days prior to the earthquake, relative to the median value of 1–12 May, whereas the increase was much less significant over Yamagawa (31.2°N, 130.6°E) and Okinawa (26.7°N, 128.2°E) in Japan. Combining the data from the network of 58 global positioning system receivers around China and the global ionospheric map, the variations of the total electron content reveal the region where enhancement persisted for a long period to be within longitudes 90°–130°E. Our results suggest that this abnormal enhancement is most possibly a seismo-ionospheric signature.

Error analysis of Abel retrieved electron density profiles from radio occultation measurements

Abstract: . This letter reports for the first time the simulated error distribution of radio occultation (RO) electron density profiles (EDPs) from the Abel inversion in a systematic way. Occultation events observed by the COSMIC satellites are simulated during the spring equinox of 2008 by calculating the integrated total electron content (TEC) along the COSMIC occultation paths with the "true" electron density from an empirical model. The retrieval errors are computed by comparing the retrieved EDPs with the "true" EDPs. The results show that the retrieved NmF2 and hmF2 are generally in good agreement with the true values, but the reliability of the retrieved electron density degrades in low latitude regions and at low altitudes. Specifically, the Abel retrieval method overestimates electron density to the north and south of the crests of the equatorial ionization anomaly (EIA), and introduces artificial plasma caves underneath the EIA crests. At lower altitudes (E- and F1-regions), it results in three pseudo peaks in daytime electron densities along the magnetic latitude and a pseudo trough in nighttime equatorial electron densities.

Rotating solar coronal holes and periodic modulation of the upper atmosphere

Abstract: [1] We report discovery of a solar-terrestrial connection between rotating solar coronal holes and density variations in Earth's thermosphere. Specifically, during 2005, a 9-day recurrence of fast streams in the solar wind exists due to solar coronal holes distributed roughly 120 degrees apart in longitude; this periodicity is transmitted to the geospace environment where it modulates geomagnetic activity and thermospheric densities derived from accelerometer measurements on the CHAMP satellite. Our discovery demonstrates a solar-terrestrial connection that has not been appreciated before, and by its nature is characterized by an element of predictability. Its potential predictability has practical relevance for collision avoidance and other applications affected by density variability in the terrestrial space environment.

Variations of electron density based on long-term incoherent scatter radar and ionosonde measurements over Millstone Hill

Abstract: [1] Measurements from the incoherent scatter radar (ISR) and ionosonde over Millstone Hill (42.6 D N, 288.5 D E) are analyzed to explore ionospheric temporal variations. The F-2 layer peak density NmF2, peak height h(m)F(2), and scale height H are derived from a Chapman a layer fitting to observed ISR electron density profiles. Diurnal, seasonal, and solar activity variations of the ionospheric characteristics are presented. Our study on the solar activity dependence of NmF2, h(m)F(2), and H indicates that the peak parameters (NmF2 and h(m)F(2)) of the F-2 layer increase with daily F-10.7 index and saturate ( or increase with a much lower rate) for very high F-10.7; however, they show almost linear dependence with the solar proxy index F-10.7p = (F-10.7 + F-10.7A)/2, where F-10.7A is the 81-day running mean of daily F-10.7. This suggests that the overall effect of solar EUV and neutral atmosphere changes on the solar activity variation of ionospheric ionization is linear with F-10.7p. The rate of change in the ionospheric characteristics with solar activity exhibits a seasonal and local time variation. Over Millstone Hill, NmF2 in summer is characterized by the evening peak in its diurnal variation, and NmF2 exhibits winter anomaly under low and high solar activity levels. The temporal variations of the topside effective scale height H-0 can be explained in terms of those in the slab thickness. The IRI model overestimates the N-e effective topside scale height over Millstone Hill; therefore our analysis for the effective topside scale height from the Millstone Hill measurements might help to improve the IRI topside profiles at middle latitudes.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

Abstract: The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

A new dynamic approach for statistical optimization of GNSS radio occultation bending angles for optimal climate monitoring utility

Abstract: [1] Global Navigation Satellite System (GNSS)-based radio occultation (RO) is a satellite remote sensing technique providing accurate profiles of the Earth’s atmosphere for weather and climate applications. Above about 30km altitude, however, statistical optimization is a critical process for initializing the RO bending angles in order to optimize the climate monitoring utility of the retrieved atmospheric profiles. Here we introduce an advanced dynamic statistical optimization algorithm, which uses bending angles from multiple days of European Centre for Medium-range Weather Forecasts (ECMWF) short-range forecast and analysis fields, together with averaged-observed bending angles, to obtain background profiles and associated error covariance matrices with geographically varying background uncertainty estimates on a daily updated basis. The new algorithm is evaluated against the existing Wegener Center Occultation Processing System version 5.4 (OPSv5.4) algorithm, using several days of simulated MetOp and observed CHAMP and COSMIC data, for January and July conditions. We find the following for the new method’s performance compared to OPSv5.4: 1.) it significantly reduces random errors (standard deviations), down to about half their size, and leaves less or about equal residual systematic errors (biases) in the optimized bending angles; 2.) the dynamic (daily) estimate of the background error correlation matrix alone already improves the optimized bending angles; 3.) the subsequently retrievedrefractivityprofilesandatmospheric(temperature)profilesbenefit by improvederror characteristics,especiallyabove about 30km. Based on theseencouraging results, we work to employ similar dynamic error covariance estimation also for the observed bending angles and to apply the method to full months and subsequently to entire climate data records.

The International Reference Ionosphere 2012 – a model of international collaboration

Abstract: The International Reference Ionosphere (IRI) project was established jointly by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) in the late sixties with the goal to develop an international standard for the specification of plasma parameters in the Earth’s ionosphere. COSPAR needed such a specification for the evaluation of environmental effects on spacecraft and experiments in space, and URSI for radiowave propagation studies and applications. At the request of COSPAR and URSI, IRI was developed as a data-based model to avoid the uncertainty of theory-based models which are only as good as the evolving theoretical understanding. Being based on most of the available and reliable observations of the ionospheric plasma from the ground and from space, IRI describes monthly averages of electron density, electron temperature, ion temperature, ion composition, and several additional parameters in the altitude range from 60 km to 2000 km. A working group of about 50 international ionospheric experts is in charge of developing and improving the IRI model. Over time as new data became available and new modeling techniques emerged, steadily improved editions of the IRI model have been published. This paper gives a brief history of the IRI project and describes the latest version of the model, IRI-2012. It also briefly discusses efforts to develop a real-time IRI model. The IRI homepage is at http://IRImodel.org.

Pulsed oxidation and biological evolution in the Ediacaran Doushantuo Formation

Abstract: Recent geochemical data from Oman, Newfoundland, and the western United States suggest that long-term oxidation of Ediacaran oceans resulted in progressive depletion of a large dissolved organic carbon (DOC) reservoir and potentially triggered the radiation of acanthomorphic acritarchs, algae, macroscopic Ediacara organisms, and, subsequently, motile bilaterian animals. However, the hypothesized coupling between ocean oxidation and evolution is contingent on the reliability of continuous geochemical and paleontological data in individual sections and of intercontinental correlations. Here we report high-resolution geochemical data from the fossil-rich Doushantuo Formation (635–551 Ma) in South China that confirm trends from other broadly equivalent sections and highlight key features that have not been observed in most sections or have received little attention. First, samples from the lower Doushantuo Formation are characterized by remarkably stable δ13Corg (carbon isotope composition of organic carbon) values but variable δ34SCAS (sulfur isotope composition of carbonate-associated sulfate) values, which are consistent with a large isotopically buffered DOC reservoir and relatively low sulfate concentrations. Second, there are three profound negative δ13Ccarb (carbon isotope composition of carbonate) excursions in the Ediacaran Period. The negative δ13Ccarb excursions in the middle and upper Doushantuo Formation record pulsed oxidation of the deep oceanic DOC reservoir. The oxidation events appear to be coupled with eukaryote diversity in the Doushantuo basin. Comparison with other early Ediacaran basins suggests spatial heterogeneity of eukaryote distribution and redox conditions. We hypothesize that the distribution of early Ediacaran eukaryotes likely tracked redox conditions and that only after ≈551 Ma (when Ediacaran oceans were pervasively oxidized) did evolution of oxygen-requiring taxa reach global distribution.

An update to the Horizontal Wind Model (HWM): The quiet time thermosphere

Abstract: The Horizontal Wind Model (HWM) has been updated in the thermosphere with new observations and formulation changes. These new data are ground-based 630 nm Fabry-Perot Interferometer (FPI) measurements in the equatorial and polar regions, as well as cross-track winds from the Gravity Field and Steady State Ocean Circulation Explorer (GOCE) satellite. The GOCE wind observations provide valuable wind data in the twilight regions. The ground-based FPI measurements fill latitudinal data gaps in the prior observational database. Construction of this reference model also provides the opportunity to compare these new measurements. The resulting update (HWM14) provides an improved time-dependent, observationally based, global empirical specification of the upper atmospheric general circulation patterns and migrating tides. In basic agreement with existing accepted theoretical knowledge of the thermosphere general circulation, additional calculations indicate that the empirical wind specifications are self-consistent with climatological ionosphere plasma distribution and electric field patterns.