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Abstract. We have investigated the origin of low-speed winds observed in association with active regions near the equator at times of solar activity minimum. The solar wind velocity distribution on a source surface at 9..5 R, is derived by interplanetary scintillation tomographic analysis, and compact low-speed regions in it are investigated in relation to active regions and large-flux-expansion regions. We show that although the low-speed regions tend to be located near active regions, they are more closely associated with large flux expansion from the vicinity of active regions. We find that slow solar wind does not arise from closed magnetic loops above an active region, but instead the low-speed stream originates from the vicinity of one polarity side of the active region. Therefore the low-speed stream, unlike the helmet streamer, has a single magnetic polarity. This can explain why conapact low-speed streams are often not associated with a hellospheric current sheet.

We report on a clear solar-cycle variation of the Sun’s shadow in the 10 TeV cosmic-ray flux observed by the Tibet air shower array during a full solar cycle from 1996 to 2009. In order to clarify the physical implications of the observed solar cycle variation, we develop numerical simulations of the Sun’s shadow, using the potential field source surface model and the current sheet source surface (CSSS) model for the coronal magnetic field. We find that the intensity deficit in the simulated Sun’s shadow is very sensitive to the coronal magnetic field structure, and the observed variation of the Sun’s shadow is better reproduced by the CSSS model. This is the first successful attempt to evaluate the coronal magnetic field models by using the Sun’s shadow observed in the TeV cosmic-ray flux.

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On 11 and 12 May 1999, the Earth was engulfed by an unusually low‐density (<1 cm−3) and low‐velocity (<350 km s−1) solar wind for a period of over 1 day. Extensive studies of this unusual event that occurred during Carrington rotation 1949 (CR1949), using both ground‐based and space‐based in situ observations, have not as yet been able to identify the cause or the solar source of this event. Using solar wind velocity measurements from the four‐station IPS observatory of the Solar‐Terrestrial Environment Laboratory (STEL), Toyokawa, Japan, we investigate the structure of the solar wind in May 1999 during CR1949. IPS observations from STEL were used to make tomographic velocity maps to identify and delineate the extent and morphology of the stable solar wind flows during CR1949 in the vicinity of the Earth. Combined with in situ measurements of the interplanetary magnetic field (IMF), potential field computations of the solar magnetic fields in the period, and HeI 10830Å observations of coronal hole boundaries during CR1949, we have identified the source region of the unusual flows and have shown that the flow responsible for the “disappearance event” was a stable unipolar flow originating in the vicinity of a large midlatitude active region AR8525, located at ∼18°N and between heliographic longitudes 280° and 300°. Earlier workers have speculated that such events may be caused by the large‐scale restructuring of the solar magnetic field at the maximum of each solar cycle. However, by identifying the solar source and nature of this event, we believe that at least in this particular case, the association with global, large‐scale solar phenomena like the periodic 11‐year solar polar field reversal is most likely to be coincidental.