[1] The daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100--120 km altitude region within ±2°latitude of the dip equator. A unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the horizontal (H) component between a magnetometer placed directly on the magnetic equator and one displaced 6°--9°away. The difference between these measured H values provides a direct measure of the daytime electrojet current and, in turn, the magnitude of the vertical E Â B drift velocity in the F region ionosphere. This paper discusses a recent study where 27 months of magnetometer H component observations and daytime, vertical E Â B drift velocities were obtained in the Peruvian longitude sector between August 2001 and December 2003. In order to establish the relationships between DH and E Â B drift velocities for the 270 days of observations, three approaches were chosen: (1) a linear regression analysis, (2) a multiple regression approach, and (3) a neural network approach. The neural network method gives slightly lower RMS error values compared with the other two methods. The relationships for all three techniques are validated using an independent set of E Â B drift observations from the Jicamarca incoherent scatter radar (ISR) located at Jicamarca, Peru. The techniques presented here will be incorporated into a recently developed, real-time Global Assimilation of Ionospheric Measurements (GAIM) model.

[1] The upper atmosphere and ionosphere exhibit variability on spatial and temporal scales characteristic of tides and planetary waves originating in the lower atmosphere. To study their generation, vertical propagation, possible nonlinear interactions and effects a new Whole Atmosphere Model (WAM) has been developed as part of the Integrated Dynamics through Earth's Atmosphere (IDEA) project. WAM is a 150-layer general circulation model based on the US National Weather Service's operational Global Forecast System (GFS) model extended upward to cover the atmosphere from the ground to about 600 km. First simulations reveal the presence of migrating and nonmigrating tides modulated at planetary wave periods in the upper atmosphere. Comparisons with observations from the TIMED satellite in the lower thermosphere show that WAM reproduces the seasonal variability of tides remarkably well, including the diurnal eastward harmonic with zonal wavenumber 3 (DE3) recently implicated in the observed spatial morphology of the ionosphere. Citation: Akmaev, R.

[1] A whole atmosphere model has been developed to demonstrate the impact of terrestrial weather on the upper atmosphere. The dynamical core is based on the NWS Global Forecast System model, which has been extended to cover altitudes from the ground to 600 km. The model includes the physical processes responsible for the stochastic nature of the lower atmosphere, which is a source of variability for the upper atmosphere. The upper levels include diffusive separation, wind induced transport of major species, and uses specific enthalpy as the dependent variable, to accommodate composition dependent gas constants and specific heats. A one-year model simulation reveals planetary waves explicitly up to 100 km altitude. At higher altitude, multi-day periodicities in the dynamics appear as a modulation of tidal amplitudes, particularly the migrating semi-diurnal tide in the lower thermosphere dynamo region. The penetration of planetary wave periodicities from tropospheric weather into the upper atmosphere can explain terrestrial weather sources of variability in the thermospheric and ionospheric. Citation: Fuller-Rowell, T. J., et al. (2008), Impact of terrestrial weather on the upper atmosphere, Geophys.

No abstract

[1] We extend a Kalman filter technique for GPS total electron content (TEC) estimation by explicitly accounting for the contribution to the line-of-sight TEC from the plasmasphere. The plasmaspheric contribution is determined by integrating the electron density predicted by the Carpenter-Anderson model along GPS raypaths and allowing the Kalman filter to scale the results to fit the observations. The filter also estimates the coefficients of a local fit to the ionospheric TEC and the receiver and satellite instrumental biases. We compare algorithm results with and without the plasmasphere term for three GPS receivers located at different latitudes. We validate the approach by comparing ionospheric TEC estimates with Advanced Research Projects Agency Long-range Tracking and Instrumentation Radar measurements along coincident lines of sight to calibration objects in low Earth orbit. We find the technique is effective at separating the ionospheric and plasmaspheric contributions to the TEC by exploiting differences in the spatial distributions of electron density, and the time scales on which they vary, in these two regions.

1] Navigation and communication, Department of Defense and civilian, customers rely on accurate, lowlatitude specification of ionospheric parameters, globally, that are not currently realistic on a day-to-day basis. This paper describes, demonstrates, and speculates about the data sets that are required inputs to the operational ionospheric models that will correct these deficiencies. In order to investigate quiet time, vertical E Â B drift velocities at two different longitude sectors, magnetometer observations were obtained for the period between January 2001 and December 2004 from the magnetometers at Jicamarca (0.8°N dip latitude) and Piura (6.8°N dip latitude) in Peru and from Davao (1.4°S dip latitude) and Muntinlupa (6.3°N dip latitude) in the Philippine sector. We choose only geomagnetically ''quiet'' days, when the 3-hourly Kp value never exceeds a value of 3 over the entire day, and when the daily Ap value is less than 10. These are ''binned'' into three seasons, December solstice, equinox, and June solstice periods. A neural network trained for the Peruvian sector was applied to each of the days in both the Peruvian and Philippine sectors, providing DH-inferred vertical E Â B drift velocities between 0700 and 1700 local time. For each season, the average E Â B drift velocity curves are compared with the Fejer-Scherliess, climatological E Â B drift velocity curves in both the Peruvian and Philippine sectors. In the Peruvian sector, the comparisons are excellent, and in the Philippine sector they are very good. We demonstrate that realistic magnetometerinferred E Â B drifts can be obtained in the Peruvian sector on a day-to-day basis and speculate that on the basis of the average, quiet day comparisons, realistic E Â B drifts can be obtained on quiet days in the Philippine sector.

No abstract

No abstract