Xiong Hu

An asymmetry correction method for ionospheric radio occultation

The approximation of spherical symmetry of electron density is the main error source in the inversion of ionospheric radio occultation (IRO). The study in this paper shows that only even terms of the asymmetry contribute to the inversion error. An asymmetry factor for IRO is defined, and it is approximately equal to the relative error of the inversion result. The characteristics of the asymmetry factor are studied and are shown in the following: (1) the absolute value of asymmetry factor (AVAF) of a zonal occultation is much smaller than that of the meridian one; (2) higher solar activity corresponds to larger AVAF; (3) AVAF is largest in winter, second largest in equinox season, and smallest in summer; and (4) generally, AVAF at middle geomagnetic latitudes is smaller than at other latitudes, and it is large at the magnetic equator, the crest region, and the middle-latitude trough. The asymmetry factor is applied to correct the retrieved electron density, and the inversion error is greatly reduced.

Global temperature stationary planetary waves extending from 20 to 120 km observed by TIMED/SABER

Version 1.07 temperature measurements from SABER instrument on board of TIMED satellite during 2006-2007 are used to study the temperature stationary planetary waves (SPWs) from 20 to 120 km. To cover the high latitudes in both hemispheres (80 degrees S-80 degrees N) and most local times, 120-day data are combined together into one data set. The most pronounced SPW features are the large amplitudes in the upper mesosphere and lower thermosphere (UMLT), while the SPWs below 90-95 km share common features with previous observations. In both hemispheric UMLT, SPWs amplitudes are large at middle and high latitudes throughout the year while their amplitudes in tropics are small. Wave 1 activity is generally stronger than the corresponding wave 2 activity with maximum amplitudes larger than 15 K, occurring at about 60 degrees-70 degrees north or south at the altitudes between 112 km and 119 km. Wave 1 amplitudes are larger in the Southern Hemisphere (SH) than in the Northern Hemisphere (NH). Their phases are normally tilt westward with increasing height below similar to 110 km. Above this altitude, the wave 1 and wave 2 phases remain nearly unchanged with height, indicating the in situ generations and no propagations. Comparisons between the observed SPW structures and those from the NRLMSISE-00 model have been done. Result shows their consistent features below similar to 80 km and that NRLMSISE-00 model gives no SPW information from 95 to 125 km but does have longitudinal variations above similar to 125 km that are similar to the observed SPW features above similar to 110 km.

Response of mesosphere and lower thermosphere wind over mid-latitude to the 2013 major sudden stratospheric warming event

In this paper we report atmospheric wind variations during the 2013 major sudden stratospheric warming (SSW) event at Langfang (39.4°N, 116.7°E). The wind measurements by Langfang meteor radar and UK Meteorological Office (UKMO) wind data are combining used to present their anomalous behaviors response to the event. These winds reveal significant anomalies in the mesosphere and lower thermosphere (MLT) zonal wind over mid-latitude corresponding to the 2013 major warming by comparing to the observations in 2010/2011 when no major warming occurred and could be considered as the normal condition. Results show that the westward wind at 60°N during 2013 major SSW was first observed between 40 km and 53 km and then extended to lower stratosphere and mesosphere. Over mid-latitude, the eastward wind reversed to westward during January 4-15, 2013 at about 80 km with the maximum value of 48.4 m/s on January 11 by UKMO data, while the reversals of MLT daily mean zonal wind persisted from January 8 to 14 observed by meteor radar with the maximum value of 40.2 m/s at 98 km also on January 11. The period of this wind reversal and the date of the maximum wind actually coincide with the mesospheric response at high latitude to the 2013 major warming. These observations and analysis document clearly the impact of a major SSW on the MLT dynamics over the mid-latitude.

Phase-Coded Interrupted CW Signals and Processors

High resolution radars require signals with large time-bandwidth product such as CW signal and coherent pulse train (CPT). We discuss a phase-coded interrupted CW (ICW) signal which is the combination of CW signal and CPT. Phase codes used here are with perfect periodic autocorrelation. The periodic ambiguity function of ICW signals is studied including single-carrier signal and multi-carrier signal. It is interesting that the gate function has different effects on two signals and contributes to a multi-carrier ICW signal which yields nearly perfect autocorrelation. Meanwhile we also suggest an efficient receiver approach to ICW signals, which can reduce the computational burden of the processor and utilize the good properties of P3 and P4 codes.

Space-borne imager of mesospheric gravity waves

Mesospheric gravity waves play important roles in atmospheric circulation and variability. It is meaningful to obtain the features of the mesospheric gravity waves on a global scale, such as the distribution and the sources. However, limited by the field of view, the ground-based instrument can only access some local information. We developed a space-borne imager to observe the global gravity waves by collecting the O2 airglow with TDI (Time Delayed and Integration) method. The function of the imager was testified in our laboratory with a led screen, where the gravity waves were simulated and shown. On a satellite orbit with the altitude of 700 km and inclination of 73 degree, the imager can obtain the gravity waves with horizontal wavelength more than 10 km, even taking the effect induced by the earth rotation into account.

Applications of GPS-R Technique for Ocean Remote Sensing: Results of Coastal Experiment in China

results of the GPS-Reflection (GPS-R) coastal experiment in the southeast of China were given. The experimental campaign began in September 2006 and its succeeding observation was kept until March 2007. Through the ocean reflected events recorded by the Oceanpal instrument, direct and reflected correlation waveforms were obtained. Then the sea surface parameter Significant Wave Height (SWH) was retrieved and compared with an Ultrasonic Wave Gauge (UWG) measurements in situ which was regarded as the truth. The statistics shows that the mean error and stand deviation is less than 5.1cm and 10.1cm respectively. At last a potential way for deriving wave speed and direction with the delay of the autocorrelation waveforms was proposed.