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Title: Solar signals in sea level pressure and sea surface temperature
Author: Roy, Indrani
ISNI:       0000 0004 2691 6754
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2010
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We investigate solar cycle signals in 150 years of Sea Level Pressure (SLP) and Sea Surface Temperature (SST) data, using multiple regression analysis. We detect a solar signal in both SLP and SST in the North Pacific during DJF, similar to that found by Van Loon et al. (2007) but of smaller magnitude. We do not, however, identify the signal they found in the tropics. Our results do not support mechanisms for a solar influence on climate directly involving tropical SSTs. We have used different reconstructions of total solar irradiance to investigate the sensitivity of the results. The series of Krivova & Solanki and Foster give similar results to those acquired using sunspot number but the Hoyt & Schatten solar index sometimes produces different results because of mixing of the solar signal with a long-term trend. Using different approaches Labitzke and van Loon (1992) and Camp and Tung (2007), arrived at different results for a solar influence on winter stratospheric polar temperatures and its relationship to the quasi-biennial oscillation (QBO) in tropical stratospheric zonal winds. We show that these differences appear different largely because of their choices of QBO height. We also show that the effect of the QBO (30, 40 or 50 hPa) combined with solar activity reveals a clear signal in polar annular modes expressed in SLP. We show that the nature of ENSO was different before 1950s (and after1997): this may affect any solar influence. Other authors have suggested that tropical circulations were different during the intervening period. Such observation may have implications relating to the sun, tropical circulation and climate change. During 1958-1997, omission of ENSO from regression gives false warming (cooling) signal of higher (lower) solar on SST in tropics. Such analysis, accompanied by our observation that the years of peak annual sunspot number used by van Loon et al. (2007) generally falls a year or more in advance of the maximum of the smoothed DSO, provides coherence to some apparently conflicting findings. Finally, an atmosphere-ocean coupling process, (mainly involving the Pacific Ocean) is proposed to account for the solar influences. This coupling appears to be disturbed during the later half of the 20th century, probably due to climate change.
Supervisor: Haigh, Joanna Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral