Ho-Sung Choi

Dependence of GCRs influx on the Solar North-South Asymmetry

Abstract We investigate the dependence of the amount of the observed galactic cosmic ray (GCR) influx on the solar North–South asymmetry using the neutron count rates obtained from four stations and sunspot data in archives spanning five solar cycles from 1953 to 2008. We find that the observed GCR influxes at Moscow, Kiel, Climax and Huancayo stations are more suppressed when the solar activity in the southern hemisphere is dominant compared with when the solar activity in the northern hemisphere is dominant. Its reduction rates at four stations are all larger than those of the suppression due to other factors including the solar polarity effect on the GCR influx. We perform the students t -test to see how significant these suppressions are. It is found that suppressions due to the solar North–South asymmetry as well as the solar polarity are significant and yet the suppressions associated with the former are larger and more significant.

The causal relationship between plasma bubbles and blobs in the low-latitude F region during a solar minimum

Plasma density depletions (bubbles) and enhancements (blobs) with respect to the background ionosphere occur at night in the low-latitude F region. Those phenomena are understood to be either causally linked or independent. The idea of the causal relationship between bubbles and blobs is on the basis of the observations of them in the same longitude. However, the occurrence of bubbles and blobs in the same longitude can also be just a coincidence. We investigate causal linkage of bubbles and blobs using the measurements of the ion density on 5 days in June 2008 and April 2009 by the Communication/Navigation Outage Forecasting System and CHAllenging Minisatellite Payload satellites. The observations during the solar minimum show that blobs occur in broader longitudes than do bubbles and occur in any longitudes regardless of the existence of bubbles. These observations indicate that a significant portion of blobs are not associated with bubbles. Even if some blobs are associated with bubbles, those blobs are indistinguishable from those produced by other sources. Therefore, the observations of bubbles and blobs at the same longitudes do not warrant their causal relationship. The independent behavior of bubbles and blobs rather indicates that their occurrences in the same longitudes are mostly coincidences. Considering the frequent occurrence of blobs near midnight, June solstice, and the solar minimum, medium-scale traveling ionospheric disturbances are likely the major source of blobs. This idea is supported by the observations of blobs with the ionospheric disturbances in broad longitudes and latitudes.

On the Relation Between the Sun and Climate Change with the Solar North-South Asymmetry

We report the relation between the solar activity and terrestrial climate change with the solar north-south asymmetry. For this purpose, we calculate sliding correlation coefficients between sunspot numbers and earth`s mean annual temperature anomalies. Then, we compare the epoch that the sign of correlation changes with the epoch that the sign of the solar north-south asymmetry changes. We obtain that corresponding times are 1907 and 1985, respectively. Further more, these two epoches are well consistent with those of signs of the solar north-south asymmetry changes. We also obtain that the plot between sunspot numbers and temperature anomalies could be classified by 1907 and 1985. We conclude that temperature anomalies are shown to be negatively correlated with sunspot numbers when the southern solar hemisphere is more active: and vice versa.

Analysis on Space Environment from the Anomalies of Geosynchronous Satellites

AbstractWhile it is well known that space environment can produce spacecraft anomaly, defin-ing space environment effects for each anomalies is difficult. This is caused by the factthat spacecraft anomaly shows various symptoms and reproducing it is impossible. Inthis study, we try to find the conditions of when spacecraft failures happen more fre-quently and give satellite operators useful information. Especially, our study focuseson the geosynchronous satellites which cost is high and required high reliability. Weused satellite anomaly data given by Satellite News Digest which is internet newspa-per providing space industry news. In our analysis, 88 anomaly cases occurred from1997 to 2008 shows bad corelation with Kp index. Satellite malfunctions were likelyto happen in spring and fall and in local time from midnight to dawn. In addition,we found the probability of anomaly increase when high energy electron flux is high.This is more clearly appeared in solar minimum than maximum period y corresponding author