Comparison of the measured and modeled electron densities, and electron and ion temperatures in the low-latitude ionosphere during 19-21 March 1988

Abstract

Abstract.We have presented a comparison between the modeled NmF2 and hmF2, and NmF2 and hmF2 which were observed at the equatorial anomaly crest and close to the geomagnetic equator simultaneously by the Akita, Kokubunji, Yamagawa, Okinawa, Chung-Li, Manila, Vanimo, and Darwin ionospheric sounders and by the middle and upper atmosphere (MU) radar at Shigaraki (34.85 • N, 136.10 • E, Japan) during the 19-21 March 1988 geomagnetically quiet time period at moderate solar activity near approximately the same geomagnetic meridian of 201 • . A comparison between the electron, T e , and ion, T i , temperatures measured by the MU radar and those produced by the model of the ionosphere and plasmasphere is presented for 19-21 March 1988. It is shown that there is a large disagreement between the measured and modeled hmF2 from about 07:00 UT to about 11:00 UT if the equatorial E×B drift given by Scherliess and Fejer (1999) is used. The required equatorial upward E×B drift is weaker from 03:14 UT to 11:14 UT than that given by Scherliess and Fejer (1999) for the studied time period. The required modification of the E×B drift weakens the effect of the fountain in NmF2 bringing the modeled and measured hmF2 and NmF2, into reasonable agreement. The depth of the equatorial NmF2 trough in the calculated NmF2 is approximately consistent with the measured depth if the modified equatorial E×B drift is used. It has been found that the north-south asymmetries in the observed NmF2 and hmF2 about the geomagnetic equator are mainly caused by the asymmetry in the neutral wind about the geomagnetic equator. In the Northern Hemisphere, the meridional neutral wind taken from the HWW90 wind model and the NRLMSISE-00 atomic oxygen density are corrected so that the model results agree with the ionospheric sounders and MU radar observations. A theory of the primary mechanisms causing the latitude dependence of the morning and evening peaks in T e is developed. The latitude dependence of the magnitudes of these peaks in T eCorrespondence to: A. V. Pavlov (pavlov@izmiran.rssi.ru) is interpreted in terms of the corresponding dependence of the electron density. The relative role of the E×B drift and the plasma drift caused by the neutral wind in the formation and the dependence of the magnitudes of the morning and evening electron temperature peaks on the geomagnetic latitude is studied.Key words. Ionosphere (equatorial ionosphere; electric fields and currents; plasma temperature and density; ionosphere-atmosphere interactions; modeling and forecasting)

<i>F</i>-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987

“…However, the low-latitude ionosphere is special because of the constraints imposed on electron and ion motions by the magnetic field and by the zonal electric field. In agreement with the results of Pavlov et al (2004) To evaluate the relative role of the E×B drift and possible uncertainties in E in variations of N e , N i , T e , and T i , calculations have been carried out from the model when the value of E , used in producing results shown by solid lines, was During most of the daytime period, the E×B drift lifts the plasma from lower field lines to higher field lines, while during most of the nighttime period, this drift moves ions and electrons from higher to lower magnetic field lines. Simultaneously, the plasma diffuses along the magnetic field lines.…”

“…As an example, above the Akita ionosonde station, this weakening in E changes N mF 2 and hmF 2 up to a factor of 0.85-1.21 and up to the maximum value of 25 km, respectively, while the maximum electron density change is a factor of 0.83-1.5 at 400 km. In agreement with the previous study by Pavlov et al (2004), we conclude that the use of the one-dimensional time dependent model of the ionosphere and plasmasphere, which does not take into account the E×B plasma drift, leads to noticeable errors in the calculated daytime electron density of the F 2 region and a part of the topside ionosphere, even at geomagnetic latitudes of about 25 • −30 • . The measured hmF 2 presented in Figs.…”

“…As was pointed out before, we expect that the NRLMSISE-00 neutral model has some inadequacies in predicting the number densities with accuracy, and we have to change the number densities by correction factors at all altitudes to bring the modeled electron densities into agreement with the measurements. As a result of the Variations in hmF 2 are predominantly determined by variations in the thermospheric wind at the ionosonde stations, such as Akita, Kokubunji, and Darwin and over the MU radar, which locations that are far enough from the geomagnetic equator (Rishbeth, 2000;Souza et al, 2000;Pincheira et al, 2002;Pavlov, 2003;Pavlov et al, 2004), i.e. effects of the E×B plasma drift on hmF 2 and N mF 2 over these sounders and over the MU radar are much less than those caused by the plasma drift due to the neutral wind.…”

“…As far as the authors know, our investigation is the first theoretical study of the role of variations in the neutral winds, temperature, and densities in producing the north−south asymmetry in the storm-time electron density. Otsuka et al (1998) found that the occurrence and strength of the morning and evening peaks in T e over the MU radar depend on altitude, season, and solar activity under magnetically quiet conditions during 1986-1995. Pavlov et al (2004 studied, for the first time, the latitude dependence of the occurrence and strength of the morning and evening peaks in T e and the mechanisms causing these peaks in the lowlatitude ionosphere during geomagnetically quiet-time conditions of 19-21 March 1988.…”

“…Otsuka et al (1998) found that the occurrence and strength of the morning and evening peaks in T e over the MU radar depend on altitude, season, and solar activity under magnetically quiet conditions during 1986-1995. Pavlov et al (2004 studied, for the first time, the latitude dependence of the occurrence and strength of the morning and evening peaks in T e and the mechanisms causing these peaks in the lowlatitude ionosphere during geomagnetically quiet-time conditions of 19-21 March 1988. In this work, we report the first results obtained from a study of the latitude dependence of the occurrence and strength of the morning and evening peaks in T e and the mechanisms causing these peaks in the low-latitude ionosphere during the 25-27 August 1987 geomagnetically storm-time period.…”