Low Solar Cycle Research Articles

Impact of solar and geomagnetic activities on total column ozone in China

Dynamic impacts on sunspot number (SSN), solar radio flux at 10.7 cm (F10.7) and amplitude antipodal (aa) index influencing long-term trends of total column ozone (TCO) obtained from three stations; Xianghe (39.975°N, 116.37°E), Linan (30.3°N, 119.73°E), and Kunming (25.03°N, 102.683°E) over China have been studied. Descriptive, regression and neural network training techniques are used from 1980 to 2018. The annual mean TCO concentrations are 333.61 ± 1.15 DU, 280.87 ± 0.58 DU, and 260.33 ± 0.49 DU at Xianghe, Linan, and Kunming stations, respectively. The mean monthly peak TCO values are ~417.13 DU (March), 316.79 DU (April), and 291.03 DU (April) at Xianghe, Linan, and Kunming, respectively. Irrespective of the decreasing seasonal trend during spring at Xianghe, the springtime TCO amount is greater than the TCO values in other seasons at all stations. Our analyses show direct forcing of SSN, F10.7, and aa on TCO changes throughout the different periods considered. At Xianghe, the value of r ranges between 0.09 and 0.48 and the p-value < 0.05 whereas the most contributing factor is aa index (about 40 %) to ozone enhancement. There is a dramatic improvement of the impact of the quasi-biennial oscillation (QBO)-modulated (70 hPa and 50 hPa) SSN, F10.7, and aa on TCO during winter in all the stations particularly the aa, which appreciated from ~40 % to 66 %. Ozone is affected negatively during descending and low solar cycle (SC) phases whereas it enhances during ascending and high SC phases with 30 hPa QBO as the most active force of enhancement. Our finding is a profitable tool for atmospheric model development, which could be used to predict future phenomena.

Solar cycle modulation of the connection between boreal winter ENSO and following summer South Asia high

In this study, the solar cycle modulation of the connection between boreal winter El Niño-South Oscillation (ENSO) and following summer South Asia High (SAH) are revealed. For El Niño accompanied by low solar cycle (EL & LS) or La Niña accompanied by low solar cycle (LA & LS), the boreal winter ENSO prominently affects the following summer's SAH variation. The SAH is enhanced (weakened) and expanded (narrowed) in the meridional and zonal directions in the EL & LS (LA & LS) phase. The composite difference in the SAH between El Niño and La Niña events is obviously stronger in the low solar cycle phase. In low solar cycle phase, El Niño signal and charging process are stronger, which lead to stronger warming sea surface temperature (SST) appear in tropical Indian Ocean and Maritime Continent extending to northwestern Pacific, resulting in larger SAH variations via warming tropospheric temperature. However, for El Niño with a high solar cycle (EL & HS) or La Niña with a high solar cycle (LA & HS), the variations in the SAH and the composite difference of the SAH between El Niño and La Niña events are quite weak in the high solar cycle phase. The charging process over tropical Indian Ocean induced by El Niño is weaker in the high solar cycle phase, which leads to weaker warming SST appear over tropical Indian Ocean, resulting in smaller SAH variations.Further investigation based on longer historic data also ensures that the 11-year solar cycle modulates the ENSO-SAH connection, with a more robust connection in the low solar cycle phase. The 11-year solar cycle should be considered when investigating the connection between the preceding winter ENSO and following summer SAH variations.

Traveling Ionosphere Disturbance Signatures on Ground‐Based Observations of the O(1D) Nightglow Inferred From 1‐D Modeling

AbstractThis paper reports our simulations of the volume emission rate of the O(1D) redline nightglow perturbed by waves traveling across the thermosphere at around 250 km altitude. Waves perturb the electronic and neutral background densities and temperatures in the region and modify the O(1D) layer intensity as it is captured by ground‐based nightglow instruments. The changes in the integrated volume emission rate are calculated for various vertical wavelengths of the perturbations. We demonstrate that, as the solar activity intensifies, the vertical scales of most likely observable TID waves become larger. For high solar activity, we demonstrate that only waves presenting vertical wavelengths larger than 360 km are likely to be observed. The variation of the range of likely observable vertical wavelengths with the solar cycle offers a plausible explanation for the low occurrence rate of TID in measurements of the redline nightglow during high solar activity periods. We have compared our results with those of Negale et al. (2018; https://doi.org/10.1029/2017JA024876) and Paulino et al (2018; https://doi.org/10.5194/angeo-36-265-2018) to verify that observed vertical wavelengths distribute around 140–210 km, in good correspondence with our predicted threshold wavelength 160 km for very low solar cycle period.

Evaluation of ionospheric models for Central and South Americas

This work shows a 20-month statistical evaluation of different Total Electron Content (TEC) estimators for the Central and South America regions. The TEC provided by the International GNSS Service (IGS) in the area covered around the monitoring GNSS stations are used as reference values, and they are compared to TEC estimates from the physics-based (Sheffield University Plasmasphere Ionosphere Model—PIM) and the empirical (Neustrelitz TEC Model-Global—NTCM-GL) models. The mean TEC values show strong dependence on both solar activity and seasonal variation. A clear response was noticed for a period close to 27 days due to the mean solar rotation, as seen in the solar flux measurements. Consistently, the mean TEC values present an annual variation with maxima during December solstices for southern stations with geographic latitudes greater than 25° S. Semi-annual dependence has been observed in TEC for the sector between ±25° of geographical latitude but with modulations caused by fluctuation in the solar radiation. We observed a high correlation between solar radio flux F10.7 and NTCM-GL outputs. The fast increases in F10.7 index have caused significant differences between IGS data and NTCM-GL results mainly for equatorial and low latitudes. For the initial months of the evaluated period (January–April, 2016), the errors of the physics-based model were considerably larger, mainly near the equatorial ionization anomaly. The discrepancies observed in SUPIM results are mainly due to inputs of solar EUV flux. The EUVAC model has underestimated EUV flux between January and April, 2016, when the solar activity was moderated and Solar2000 model has overestimated such flux during low solar cycle period between May and August, 2017. In relation to IGS data, the two assessed models presented smaller differences during the June solstice season of 2016.

Does a low solar cycle minimum hint at a weak upcoming cycle?

The maximum amplitude (Rm) of a solar cycle, in the term of mean sunspot numbers, is well-known to be positively correlated with the preceding minimum (Rmin). So far as the long term trend is concerned, a low level of Rmin tends to be followed by a weak Rm, and vice versa. We found that the evidence is insufficient to infer a very weak Cycle 24 from the very low Rmin in the preceding cycle. This is concluded by analyzing the correlation in the temporal variations of parameters for two successive cycles.

Ohmic heating of the polar F region by HF pulses

A study of the modifications produced by high‐power, high‐frequency (HF) waves in the F region of a quiet (low solar cycle) polar ionosphere is presented. In the polar geometry, maximum ohmic heating occurs producing significant changes to the zero‐order electron temperature and density profiles. The temporal and spatial aspects of these changes are calculated, and their effects on relevant ionospheric parameters, such as the dc conductivity tensor, are found. An interesting result is the generation of a density depression at the reflection point of the HF waves. The dependence of ohmic heating on HF pump parameters and peak background density is considered.