Using TEC measurements from the dense network of GPS sites GEONET, we have obtained the first GPS-TEC image of the space structure of medium-scale traveling wave packets (MS TWP) excited by the morning solar terminator (ST). We found that ST-generated wave packets have dura- tion of about 1-2 h and time shift of about 1.5-6 h after the morning ST appearance at an altitude of 300 km. The TWP wave front extends along the morning ST line with the an- gular shift of about 20 . The time period and wave-length of ST-generated wave packets are about 10-20 min and 200- 300 km, respectively. The velocity of the TWP phase front traveling is of about 300 m/s. The space image of MS TWP manifests itself in pronounced anisotropy and high coherence over a long distance of about 2000 km. ing over the USA, Europe, and Japan. The author found two main types of the observed TEC disturbance: large-scale (LS) 60-min variations with amplitude of about 0.5-1 TECU and medium-scale (MS) 15-min variations with amplitude of about 0.05-0.1 TECU (TECU is 10 16 m 2 ). The first type of disturbances was predicted in theoretical investigations and registered earlier using different methods of ionosphere ra- dio sounding. The second type of the observed TEC dis- turbances is traveling wave packets (TWP) generated when the time derivative of TEC is at its maximum. These TWPs have duration of about 1-2 h and time shift of about 1.5-2.5 h after the ST appearance at an altitude of 100 km. These ST- generated wave packets have been found for the first time. The relative amplitude of TEC wave packets is sufficiently low (of about 0.2%). This may be the main reason why such a phenomenon has been unknown to date. To identify ST-generated wave packets it is insufficient to register the TEC time dependence (Afraimovich, 2008). Their spatial structure needs to be determined. But only a dense network of stations can display wave packets. We employ data from the Japanese GPS network GEONET (about 1225 stations in all). At present it is the largest re- gional GPS network in the world (ftp://terras.gsi.go.jp/data/ GPS products/). The goal of this paper is to obtain the first GEONET GPS- TEC image of the space structure of ST-generated MS TWP.
[1]
V. Somsikov.
On mechanisms for the formation of atmospheric irregularities in the solar terminator region
,
1995
.
[2]
V. Somsikov.
A spherical model of wave generation in the atmosphere by the solar terminator
,
1987
.
[3]
John A. Klobuchar,et al.
Design and characteristics of the GPS ionospheric time delay algorithm for single frequency users
,
1986
.
[4]
T. Beer.
On atmospheric wave generation by the terminator
,
1978
.
[5]
Samuel H. Francis,et al.
A theory of medium‐scale traveling ionospheric disturbances
,
1974
.
[6]
B. Ganguly,et al.
On the formation of atmospheric inhomogeneities in the solar terminator region
,
1995
.
[7]
E. L. Afraimovich,et al.
First GPS-TEC evidence for the wave structure excited by the solar terminator
,
2008
.
[8]
H. Teitelbaum,et al.
Generation of gravity waves by inhomogeneous heating of the atmosphere
,
1980
.
[9]
Jean-Bernard Minster,et al.
Detection of ionospheric perturbations using a dense GPS array in Southern California
,
2003
.
[10]
J. Ping,et al.
Directivity and apparent velocity of the coseismic ionospheric disturbances observed with a dense GPS array
,
2005
.
[11]
Y. Otsuka,et al.
Medium‐scale traveling ionospheric disturbances detected with dense and wide TEC maps over North America
,
2007
.
[12]
K. Hocke,et al.
A review of atmospheric gravity waves and travelling ionospheric disturbances: 1982-1995
,
1996
.