Solar Signals in Observation Indeed Implied Enhanced Predictability Since 1977
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Pure and Applied Geophysics
Solar Signals in Observation Indeed Implied Enhanced Predictability Since 1977 INDRANI ROY1 Abstract—This is a Correspondence following the undermentioned paper: Chiodo et al. (Nat Geosci 12:94–99, 2019).
The sun NAO connection attracted enough attention over the last few decades and explored in various modelling as well as observational studies. A modelling work (Ineson et al. 2011) using UK Met Office Unified Model analysed the regional impact of the solar 11-year cycle on NAO, during boreal winter and found an in-phase relationship. It was interesting to study the robustness of such a proposed association between the sun and NAO (Ineson et al. 2011). Various studies already addressed and explored that issue in detail using observation (Roy 2018a, 2020; Roy and Kriplani 2018). Those noted that such inphase connection is clearly noticed since 1977, though inconsistent over the last 150 years (Roy and Haigh 2010) and suggested variations in earlier periods (Roy 2014). Solar lag connections in observation were also seen sensitive to the period chosen (earlier or later) (Roy 2020), though strongest around the North Atlantic in lag year-1 and year-2 in later decades of the last century [(Roy 2020), Fig. 6 from there]. Here we show the sun-NAO connection indeed suggested enhanced predictability since 1977 in observation for zero lag case. This is established by using two different data sources and for two different meteorological parameters (HadSLP2/ HadSLP2r_lowvardata for Sea Level Pressure (SLP) and NCEP reanalyses for geopotential height) (Fig. 1). It also consulted different methodology, one is Compositing technique and the other Multiple Linear Regression (MLR) technique with AR(1) noise model (Roy 2018b). For MLR, amplitude of
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IRDR, University College London, London, UK. E-mail: [email protected]
components of SLP variability (max–min, hPa) due to the sun is presented. Both methods indicated a strong in-phase sun–NAO relationship. Figure 1 showed few results, but we have increased confidence that using various other observational/reanalyses data and applying other methodologies will also indicate a similar solar signature since 1977. A relevant very recent observational study is also worthmentioning (Hedi 2019). That indicated a robust solar signature in China during winter which is originated from the north Atlantic. The signature is very significant since the 1970s and consistent with solar–NAO relationship as noted in other observed work. The modelling work of Chiodo et al. (2019) however could not capture any robust connection between the sun and NAO. Following the above discussion of an overall 150-years period using observation, such a result is not unlikely. Also, for models, the peak and trough of various climate modes are not synchronised with observed climate modes of variability (Roy 2017, 2018c). The decadal signature part for some climate features is well presented in models, in general; but unfortunately, those do not match with observed peak and trough (Turner
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