S. Nozawa

Simultaneous EISCAT Svalbard radar and DMSP observations of ion upflow in the dayside polar ionosphere

[1]xa0Regions where dayside field-aligned (FA) ion upflows occur are identified, and the relative occurrences and characteristics are compared. The study is based on ∼170 simultaneous events observed with the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and spacecraft from the DMSP. We found that ion upflows occur not only in the cusp and cleft (the low-altitude portion of the low-latitude boundary layer), which traditionally have been regarded as regions of ion upflow, but also in the region connected to the mantle. Ion upflows are less frequently seen in the boundary plasma sheet (BPS) and are very rarely seen in the central plasma sheet at high latitude on the dayside. Almost all of the events in which the average FA ion velocity is >100 m s−1 are associated with relatively high soft electron precipitation (differential energy flux of electrons at 100 eV > 107 eV cm−2 s−1 sr−1 eV−1), although soft electron precipitation with similarly high flux exists also in the BPS, where the ion velocities are mostly <100 m s−1. These results indicate that soft particle precipitation is the predominant energy source driving ion upflow in the topside ionosphere, but it triggers ion upflow effectively not in the BPS, only in the other high-latitude regions on the dayside.

A comparison of mesosphere and lower thermosphere neutral winds as determined by meteor and medium‐frequency radar at 70°N

[1]xa0There has been much discussion as to the veracity of neutral wind measurements made using medium-frequency radar (MFR) employing the spaced-antenna technique. Such systems are able to operate continuously, providing information on mesosphere and lower thermosphere dynamics with typical resolutions of 3 km in altitude and 5 min in time, and thus represent a low-cost monitoring of the atmosphere. It is similarly important to be able to trust the results, and therefore we make a dedicated comparison between the Tromso MFR (70°N, 19°E) and the newly installed and colocated Nippon/Norway Tromso meteor radar. The agreement is particularly good between 75 and 85 km.

The quasi 2‐day wave observed in the polar mesosphere: Comparison of the characteristics observed at Tromsø and Poker Flat

[1]xa0A comparison of the quasi 2-day wave (Q2DW) observed at Tromso (69.6°N, 19.2°E) and Poker Flat (65.2°, 147.6°W) is presented at four heights of 70, 76, 82, and 88 km using wind data taken for ∼4 years, from 1 November 1998 to 7 November 2002. The characteristics of the Q2DW such as seasonal variation, occurrence of period of maximum amplitude, ratio of meridional to zonal amplitudes, shape of altitude profile of phase, and modulation of amplitude at a 4–10 days rate found at Poker Flat are very similar to those found at Tromso reported by Nozawa et al. [2003]. The activity of the Q2DW is higher in winter than in summer for meridional and zonal components at the two sites. Long-term variation (i.e., seasonal variation) of the Q2DW is found to be similar between the two sites, while short-term variations (i.e., over several days) do not synchronize well with each other. The ratio of amplitudes of the Q2DW between the two sites varies mainly between 0.5 and 2, and there is no significant preference toward either site. Phase differences of Q2DWs between the two sites are examined, and it is found that in-phase-like events are more frequently seen than out-of-phase-like events at 76, 82, and 88 km in winter and at 88 km in summer. This can be interpreted to mean that the zonal wave number of the Q2DW appears to be 2 or 4 more often than 3 in the polar upper mesosphere. These results suggest that observed Q2DWs have features consistent with the Rossby gravity wave mode, but the amplitude and phase of the Q2DW are affected significantly by local sources. A possibility that the observed Q2DW is an eastward moving wave is also discussed.

Solar activity dependence of ion upflow in the polar ionosphere observed with the European Incoherent Scatter (EISCAT) Tromsø UHF radar

The influence of solar activity upon ion upflow in the polar ionosphere was investigated using data obtained by the European Incoherent Scatter (EISCAT) Tromso UHF radar between 1984 and 2008. In a ...

Vertical ion motion observed with incoherent scatter radars in the polar lower ionosphere

[1]xa0Vertical ion velocities in excess of a few tens m s−1 have been found in the lower ionosphere (95–105 km) at high latitudes. Statistics using data from the European Incoherent Scatter (EISCAT) Tromso UHF radar are performed to understand general character of vertical motions in the lower ionosphere for geomagnetically quiet conditions. We estimate the probability distribution function for the real vertical ion velocity, taking into account the measurement uncertainty. This calculation suggests that while most vertical ion velocities have amplitudes smaller than 20 m s−1 at 100 km level, the magnitudes larger than 20 m s−1 are observed as statistical exception. To understand if these large vertical motions in the lower ionosphere are associated with thermospheric motions, differences between ion and neutral wind velocities are calculated using data from experiments with the Sondrestrom incoherent scatter radar on 5 and 12 September 2003. The vertical ion velocities show magnitudes larger than 20 m s−1 below 103 km where the ion velocity is considered to be equal to the neutral wind velocity during the experiments according to calculations of the velocity difference.

Temperature enhancements and vertical winds in the lower thermosphere associated with auroral heating during the DELTA campaign

[1] A coordinated observation of the atmospheric response to auroral energy input in the polar lower thermosphere was conducted during the Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign. N2 rotational temperature was measured with a rocket-borne instrument launched from the Andoya Rocket Range, neutral winds were measured from auroral emissions at 557.7 nm with a Fabry-Perot Interferometer (FPI) at Skibotn and the KEOPS, and ionospheric parameters were measured with the European Incoherent Scatter (EISCAT) UHF radar at Tromso. Altitude profiles of the passive energy deposition rate and the particle heating rate were estimated using data taken with the EISCAT radar. The local temperature enhancement derived from the difference between the observed N2 rotational temperature and the MSISE-90 model neutral temperature were 70–140 K at 110–140 km altitude. The temperature increase rate derived from the estimated heating rates, however, cannot account for the temperature enhancement below 120 km, even considering the contribution of the neutral density to the estimated heating rate. The observed upward winds up to 40 m s �1 seem to respond nearly instantaneously to changes in the heating rates. Although the wind speeds cannot be explained by the estimated heating rate and the thermal expansion hypothesis, the present study suggests that the generation mechanism of the large vertical winds must be responsible for the fast response of the vertical wind to the heating event.

Angular dependence of pump-induced bottomside and topside ionospheric plasma turbulence at EISCAT

[1]xa0We experimentally observe the location and angular size of the high-frequency (HF) radio window in the bottomside ionosphere, which permits radio wave propagation to the topside ionosphere, with high angular resolution at the European Incoherent Scatter (EISCAT) facility. HF pump-induced ion line enhancements were observed by the EISCAT UHF incoherent scatter radar on the ionospheric bottomside and topside. The radar zenith angle was scanned in small steps in the magnetic meridian. The HF pump duty cycle was deliberately kept low enough to minimize the growth of artificial field-aligned irregularities. The locations of the bottomside radio window and topside enhanced radar echoes are consistent with the expected position determined by ray tracing performed using the observed plasma densities.

Mesoscale observations of Joule heating near an auroral arc and ion‐neutral collision frequency in the polar cap E region

We report on the first meso-scale combined ionospheric and thermospheric observations, partly in the vicinity of an auroral arc, from Svalbard in the polar cap on 2 February 2010. The EISCAT Svalbard radar employed a novel scanning mode in order to obtain F- and E-region ion flows over an annular region centred on the radar. Simultaneously, a co-located Scanning Doppler Imager observed the E-region neutral winds and temperatures around 110 km altitude using the 557.7 nm auroral optical emission. Combining the ion and neutral data permits the E-region Joule heating to be estimated with an azimuthal spatial resolution of ∼64 km at a radius of ∼163 km from the radar. The spatial distribution of Joule heating shows significant meso-scale variation. The ion-neutral collision frequency is measured in the E-region by combining all the data over the entire field of view with only weak aurora present. The estimated ion-neutral collision frequency at ∼113 km altitude is in good agreement with the MSIS atmospheric model.

Sodium temperature/wind lidar based on laser-diode-pumped Nd:YAG lasers deployed at Tromsø, Norway (69.6°N, 19.2°E)

An Nd:YAG laser-based sodium temperature/wind lidar was developed for the measurement of the northern polar mesosphere and lower thermosphere at Tromsø (69.6N, 19.2E), Norway. Coherent light at 589 nm is produced by sum frequency generation of 1064 nm and 1319 nm from two diode laser end-pumped pulsed Nd:YAG lasers. The output power is as high as 4W, with 4 mJ/pulse at 1000 Hz repetition rate. Five tilting Cassegrain telescopes enable us to make five-direction (zenith, north, south, east, west) observation for temperature and wind simultaneously. This highly stable laser system is first of its kind to operate virtually maintenance-free during the observation season (from late September to March) since 2010.