author = "Chaitanya, P. Pavan and Patra, A. K. and Balan, Nalan and Rao, S. 
                         V. B.",
          affiliation = "{National Atmospheric Research Laboratory} and {National 
                         Atmospheric Research Laboratory} and {Instituto Nacional de 
                         Pesquisas Espaciais (INPE)} and University, Tirupati",
                title = "Unusual behavior of the low-latitude ionosphere in the Indian 
                         sector during the deep solar minimum in 2009",
              journal = "Journal of Geophysical Research Space Physics",
                 year = "2016",
               volume = "121",
               number = "7",
                pages = "6830--6843",
                month = "July",
             keywords = "deep solar minimum, equatorial ionosphere.",
             abstract = "In this paper we carry out a comparative study of the daytime 
                         (7-18 LT) behavior of the near-equatorial ionospheric F region at 
                         the end of the long deep solar minimum (2009) with respect to that 
                         of the previous normal solar minimum (1995) in the Indian 
                         longitude sector using ionosonde observations of F layer 
                         parameters, radar observations of ExB drift, and the IRI-2012 
                         (International Reference Ionosphere-2012) model. We investigate 
                         the F-2 and F-3 layer behaviors separately. The results reveal 
                         that the peak frequencies of the F layer (f(peak)), F-2 layer 
                         (f(o)F(2)), and F-3 layer (f(o)F(3)) in 2009 are consistently 
                         lower than those in 1995. Maximum difference in 
                         f(peak)/f(o)F(2)/f(o)F(3) between 2009 and 1995 observations is 
                         found in the equinoxes followed by winter and summer. The annual 
                         mean, seasonal mean, and 10day mean peak electron density 
                         (corresponding to f(peak)) in 2009 were lower than those in 1995 
                         by as much as 34%, 46%, and 65%, respectively. Solar rotation 
                         effect is less conspicuous in 2009 than in 1995, consistent with 
                         the solar rotation signature in F-10.7. Observations also show 
                         considerable amount of equinoctial asymmetry in electron density, 
                         which is found to be closely linked with the corresponding 
                         asymmetry in the vertical ExB drift. Seasonal mean peak electron 
                         densities of the F layer (corresponding to f(peak)) and the F-2 
                         layer (corresponding to f(o)F(2)) observed during the deep solar 
                         minimum of 2009 were smaller than those corresponding to IRI-2012 
                         model f(o)F(2) by as much as 45% and 50%, respectively, 
                         underlining the need to incorporate the data collected during the 
                         long deep minimum in the IRI model. The unusually weak ionosphere 
                         observed in 2009 is discussed in terms of the direct effect of the 
                         low solar EUV flux in 2009 as compared to 1995 and its indirect 
                         effects on ionospheric electric field, thermospheric composition 
                         (or O/N-2 ratio), and thermospheric neutral winds.",
                  doi = "10.1002/2015JA022061",
                  url = "http://dx.doi.org/10.1002/2015JA022061",
                 issn = "2169-9380",
             language = "en",
           targetfile = "chaitanya_unusual.pdf",
        urlaccessdate = "24 jan. 2021"