Large variations in the thermosphere and ionosphere during minor geomagnetic disturbances in April 2002 and their association with IMF B_y

Abstract

1] We investigate the variations in the thermosphere and ionosphere using multiinstrument observations during the April 2002 period, with a particular focus on periods during small geomagnetic disturbances. Large and long-lasting reductions in the daytime electron density were observed at midlatitudes by incoherent scatter radars, ionosondes, and GPS receivers. These reductions reached 30-50% and were observed over an extended longitudinal area. They propagated to middle latitudes (35-40°N) in the case of a weak geomagnetic disturbance (K p = 3À) and to low latitudes (0-10°N) in the case of a stronger disturbance (K p = 5À). Data from the GUVI instrument aboard the TIMED satellite reveal a reduction in the daytime O/N 2 ratio in the coincident area. Similar decreases are also predicted by the TIMEGCM/ASPEN model in both O/N 2 ratio and electron density, though the magnitude of the decrease from the model is smaller than observed. We suggest that these ionospheric and thermospheric disturbances result from high-latitude energy input and efficient transport of regions with reduced O/N 2 to lower latitudes. We discuss the possible role of a strong positive B y component of the interplanetary magnetic field in the transport of regions with reduced O/N 2 . Citation: Goncharenko, L., et al. (2006), Large variations in the thermosphere and ionosphere during minor geomagnetic disturbances in April 2002 and their association with IMF B y ,

Daytime F2-layer negative storm effect: what is the difference between storm-induced and Q-disturbance events?

“…3). The results of our calculations (Table 1) are confirmed by GUVI/TIMED observations, which also show a low [O]/[N 2 ] column ratio for the day of negative Q-disturbance on 16 April 2002 (Goncharenko et al, 2006). The ground state of the thermosphere with the northward meridional wind did take place on 16 April.…”

“…The ground state of the thermosphere with the northward meridional wind did take place on 16 April. According to Millstone Hill estimations, V nx was northward until 21:00 UT (Goncharenko et al, 2006, their Fig. 17).…”

Synchronous <I>Nm</I>F2 and <I>Nm</I>E daytime variations as a key to the mechanism of quiet-time F2-layer disturbances

“…The calculated Tex are close to the Millstone Hill estimates for both periods, being larger than the NRLMSISE-00 (Picone et al, 2002) model predictions by about 100 K. A similar underestimation of the NRLMSISE-00 model Tex was noted by Lei et al (2004). The O/N 2 column ratio observed with the GUVI instrument for the 15/16 April 2002 period shows a 30-50% reduction from 15 April to 16 April in the Atlantic longitudinal sector (Goncharenko et al, 2006). A direct comparison of our [O] and [N 2 ] with the GUVI column observations is problematic due to many technical reasons (Goncharenko et al, 2006), however, our O/N 2 ratio at 300 km reduced to 07:30 LT (the local time of the GUVI observations) also exhibits a 40% reduction on 16 April with respect to 15 April.…”

“…On the other hand, neither one can exclude the high-latitude impact on the global circulation and thermospheric composition. Goncharenko et al (2006), for instance, revealed a pronounced negative Q-disturbance effect using the Millstone Hill ISR and TIMED observations and attributed it to IMF B y variations.…”

On the mechanism of seasonal and solar cycleNmF2variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations

“…[29] Optical observations by Grossmann et al [2000] revealed a systematic (by 40% on average below MSIS-86) difference in atomic oxygen densities in the 130-175 km height range. The O/N 2 column ratio observed with the TIMED/GUVI instrument for the magnetically quiet period 15-16 April 2002 gave a 30-50% reduction of this ratio from 15 to 16 April in the Atlantic longitudinal sector [Goncharenko et al, 2006]. Neither MSIS-86 nor NRLMSISE-00 models describe such strong O/N 2 day-to-day variations.…”