Huixin Liu

A global distribution of the thermospheric total mass density at 400 km altitude is derived from the high‐accuracy accelerometer on board the CHAMP satellite with good temporal and spatial coverage. It shows two interesting features. One is the anomalous distribution at low latitudes. Instead of maximizing at the dayside equator, the thermospheric density shows maxima at about 20°–25° geomagnetic latitude on both sides of the equator between 10 and 20 magnetic local time. This latitudinal distri

Strong enhancements of the upper thermospheric total mass density were observed by the CHAMP satellite at approximately 400 km altitude during three geomagnetic superstorms occurring on 29–30 October 2003, 30–31 October 2003, and 20–22 November 2003. The corresponding density enhancements peaked around 400%, 500%, and 800% of the quiet‐time values in both noon and midnight sectors. The disturbances showed strong noon–midnight and hemispheric/seasonal asymmetry. In the noon sector, the average de

Using 3 years (2002–2004), over 16,400 orbits of measurements from the accelerometer on board the CHAMP satellite, we have studied the climatology of the equatorial zonal wind in the upper thermosphere. Several main features are noticed. The most prominent one is that the solar flux significantly influences both the daytime and nighttime winds. It overrides the geomagnetic activity effect, which is found to be rather limited to the nightside. An elevation of the solar flux level from F 10.7 ≈ 10

The equatorial anomaly is an interesting and important feature of the Earth's thermosphere‐ionosphere coupling in tropical regions. It is an anomalous latitudinal distribution found in both the ionized and unionized part of the atmosphere. Its equinox configuration consists of a minimum near the dip equator flanked by two maxima on both sides. The ionospheric side of this anomaly, often referred to as the equatorial ionization anomaly (EIA), has long been recognized since the 1930s. However, its

The equatorial mass density anomaly (EMA) is an anomalous latitudinal distribution of the atmospheric mass density, with its equinox configuration consisting of a density trough near the Earth's dip equator flanked by density crests around ±25° dip latitude. As a novel feature, this study reveals a pronounced 4‐peak longitudinal pattern of the EMA, which is in reminiscence of the wave‐4 like structure in the neutral wind and the equatorial ionization anomaly (EIA). It is found that the wave‐4 mo

We have investigated the solar activity dependence of the electron density at equatorial and low latitudes using 6 years (a) of measurements between 1 August 2000 and 1 August 2006 from CHAMP and compared it with the international reference ionosphere (IRI) model. The solar activity dependence observed by CHAMP at 400 km altitude exhibits significant variation with latitude, season, and local time. First, the electron density in the crest regions of the equatorial ionization anomaly (EIA) grows

The typical diurnal cycle of the midlatitude F region electron density consists of a midday maximum and a midnight minimum. However, a phase reversal of this diurnal cycle has been found to occur in three distinct regions on the globe. They are the East Asian (EA) region centered around (53°N, 150°E), the Northern Atlantic (NA) region centered around (45°N, 50°W) and the South Pacific (SP) region centered around (60°S, 110°W). The intensively reported Weddell Sea Anomaly falls inside the SP regi

Abstract. Long-term and continuous observations of mesospheric–lower thermospheric winds are rare, but they are important to investigate climatological changes at these altitudes on timescales of several years, covering a solar cycle and longer. Such long time series are a natural heritage of the mesosphere–lower thermosphere climate, and they are valuable to compare climate models or long-term runs of general circulation models (GCMs). Here we present a climatological comparison of wind observa

We have examined the longitudinal structure of the equatorial ionosphere at 400‐km altitude in the noon and postsunset local time sectors in different seasons using 6 years of F‐region plasma density observations from the CHAMP satellite. A four‐peak wave structure is observed in both local time sectors. In the noon sector at a fixed solar flux level, this structure is observed to be most prominent around September equinox and weakest around December solstice. This seasonal dependence agrees wel

[1] Thermospheric density simultaneously observed by the CHAMP and GRACE satellites in both the pre-dawn and afternoon local time sectors undergoes significant decrease across both hemispheres during the major stratospheric sudden warming (SSW) in January 2009. This decrease is largest in the equatorial region near the subsolar latitude, reaching ∼30% at 325 km, and 45% at 475 km altitude in the afternoon sector. This large density drop demonstrates a substantial cooling of about 50 Kelvin in th

We examined the thermospheric and ionospheric responses to the solar flare on 28 October 2003, utilizing simultaneous observations of the electron and neutral density from the CHAMP satellite. Rapid thermospheric response within a few minutes was observed. In addition, the neutral and plasma perturbations contrasted each other remarkably. First, their temporal development differed. Though started nearly simultaneously, the plasma perturbation developed much faster and to a larger amplitude than

Abstract The whole atmosphere model GAIA is employed to shed light on atmospheric response to the 2009 major stratosphere sudden warming (SSW) from the ground to exobase. Distinct features are revealed about SSW impacts on thermospheric temperature and density above 100 km altitude. (1) The effect is primarily quasi‐semidiurnal in tropical regions, with warming in the noon and pre‐midnight sectors and cooling in the dawn and dusk sectors. (2) This pattern exists at all altitudes above 100 km, wi

Abstract Changes of the zonal mean state of the thermosphere during the 2009 stratospheric sudden warming (SSW) have been investigated using the Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) model. Both the zonal mean thermal and dynamical structure of the thermosphere exhibit pronounced changes during the SSW in terms of zonal mean temperature and winds. First, the zonal mean temperature above 100 km altitude drops at all latitudes except for in a narrow band around 6

[1] Using ground observations of total electron content (TEC) and equatorial electrojet (EEJ) in the Asian sector, along with plasma and neutral densities obtained from the CHAMP satellite, we investigate the ionospheric electrodynamics and neutral background in this longitude sector during the major stratospheric sudden warming (SSW) in January 2009. Our analysis reveals the following prominent features. First, the TEC response in tropical regions is strongly latitude dependent, with monotonic

A solar terminator wave has been revealed in thermospheric wind and density simultaneously observed by CHAMP. The wind terminator wave is out of phase with the density terminator wave. But both have wavefronts about 30° inclined to the terminator line at low latitudes, and wavelengths ranging between 3000–5000 km. They show a clear dawn‐dusk asymmetry, with more pronounced wave signatures forming at dusk. Terminator wave is indiscernible in the dawnside wind. Most wave structures are observed at