The ionospheric Nighttime Winter Anomaly (NWA) was first reported more than three decades ago based on total electron content (TEC) and vertical sounding data. The aim of this paper is to provide further evidence that the NWA effect is a persistent feature in the Northern Hemisphere at the American and in the Southern Hemisphere at the Asian longitude sector under low solar activity conditions. The analysis of ground‐based GPS derived TEC and peak electron density data from radio occultation measurements on Formosat‐3/COSMIC satellites confirms and further supports the findings published in earlier NWA papers. So it has been confirmed and further specified that the NWA appears at longitude sectors where the displacement between the geomagnetic and the geographic equator maximizes. Here NWA peaks at around 40°–50° geomagnetic midlatitude supporting the idea that wind‐induced plasma uplifting in the conjugated summer hemisphere is the main driving force for the accumulation of ionospheric plasma in the topside ionosphere and plasmasphere. In parallel, the midsummer nighttime anomaly (MSNA) is caused at the local ionosphere. Simultaneously, interhemispheric coupling causes severe downward plasma fluxes in the conjugated winter hemisphere during night causing the NWA at low solar activity. With increasing solar activity, the downward plasma fluxes lose their impact due to the much stronger increasing background ionization that masks the NWA. It is assumed that MSNA and related special anomalies such as the Weddell Sea Anomaly and the Okhotsk Sea Anomaly are closely related to the NWA via enhanced wind‐induced uplifting of the ionosphere.

INTRODUCTIONThe concentration of cloud condensation nuclei (CCN) can significantly affect cloud microphysical processes, and in turn, several aspects of weather and climate. The aerosol-cloud interactions and its impact on climate is the least understood and therefore is a subject of intense research in recent years. For more details pertaining to the effects of aerosols on climate and on cloud processes and precipitation, one can look into the excellent reviews by (Lohmann and Feichter 2005;Rosenfeld et al. 2008).Aerosols, by acting as CCN, can perturb clouds. Their effect on earth radiative balance is the largest source of uncertainty in anthropogenic climate change (Houghton et al. 2001). A strong positive correlation exists between cloud droplet number concentration and CCN concentration, implying an increase in CCN number results in increased droplet concentration that increases reflectivity leading to climate cooling . This has been confirmed by both modeling results and field observations in marine and continental environments . Therefore, simultaneous in-situ measurements of cloud condensation nuclei and aerosol properties are crucial for establishing a quantitative relationship between cloud microphysics and the microphysical (size) and chemical properties of aerosol (Rissman et al. 2006). Amongst several outstanding issues, the most important is the creation of seasonal 3-D maps of the global distribution of CCN, which is most relevant to warm cloud formation. Considerable efforts have been made in recent years to construct a global CCN climatology, e.g., Southern Ocean (Hudson et al. 1998

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