SUFR-Sp-C

Results

The SUFR radiometer and VUSS spectrometer performed multiple measurements of the solar EUV radiation in absolute energy units (solving the calibration problem). For the first time, a new non-optical method was applied in the VUSS instrument for recording solar radiation in the vacuum ultraviolet region. As shown by the SUFR measurements, the mean value of EUV flux (<130 nm) for the observation period amounted to about 7.5 erg cm^-2 s^-1, which agrees with model calculations for the previous solar cycle.

During the solar flare of June 30, 1994 at 01:08 UT (X-ray flare of importance B4.5), SUFR recorded a 15% growth of EUV flux in the spectral region &lambda < 130 nm.

Over the observation period, characterized by low solar activity (F10,7 ~ 89-80), the UV flux in the 30.4 nm Helium line, recorded by VUSS with an accuracy no worse than 15%, ranged from 6.0 10⁹ to 7.5 10⁹ quantum cm^-2s^-1 and displayed a similar variation trend when compared with the 10cm radio flux data from Boulder and Moscow. The UV radiation, measured by VUSS, proved to be somewhat lower, than calculations based on the conventional models. Model calculations give 9 10⁹ quantum cm^-2s^-1 against the measured values, not exceeding 7,5 10⁹ quantum cm^-2s^-1. This discrepancy must be the object of further investigations because it may either point to the necessity of improvement of the solar radiation models, or to the anomalous behavior of UV fluxes near the minimum of solar cycle 22.

SUFR measurements indicated that the average UV flux for this time interval was about 7.5 erg/cm² s. This value is in accordance with results of calculations within the models generalizing the experimental data obtained in previous solar activity cycles.

For the time interval March 4-7, characterized by low solar activity (F10,7 ~ 89-90), the flux in this line measured with an accuracy better than 15 % varied within the range from 6.0•10⁹ to 7.5•10⁹ quanta sm^-2s^-1. These variations have the same tendency as for the solar radio-frequency radiation index (F10.7 ) determined at Boulder and in Moscow (also plotted at the Figure). However, the VUSS spectrometer results in the vicinity of 30.4 nm appear to be lower than model estimates. While the latter provide the value of 9•10⁹ quanta sm^-2 s^-1 the measured values do not exceed 7.5•10⁹ quanta sm^-2s^-1. This difference deserves further investigation.