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Title: Understanding diurnal temperature range changes
Author: Jackson, Lawrence Stephen
ISNI:       0000 0004 2742 0064
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2012
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Diurnal temperature range (DTR) declined over global land during 1950-2004. Climate model simulations have shown DTR is sensitive to many forcings including solar radiation, CO2, aerosols and land cover change. Relationships between DTR trends and potential forcings or feedbacks fall short of providing causal evidence due to paucity of observations and a focus on average changes over the diurnal cycle rather than changes within the diurnal cycle. Non-linear regression of seasonal and geographic variations in DTR found cloud cover, soil moisture, distance inland, solar radiation, elevation and vegetation type explained 80% of the variation in DTR. These factors are likely influential for regional DTR trends. Surface net longwave radiation was linearly related to seasonal variations in DTR and explained over 95% of the' variation in tropical regions. The NCAR SCCM model was used to simulate the response of DTR and surface energy fluxes to 2 x CO2 and -2% solar forcings. An ensemble of 24 model runs with forcing applied hourly through the diurnal cycle was replicated 20 times in 18 locations. Under CO2 forcing, the increase in DTR at the first '.···r time-step after forcing (0.01 DC) was offset by rapid adjustments and climate feedbacks during the three-day period after forcing. Rapid adjustments to surface sensible and latent heat fluxes totalled +1.55 Wm·2 driven by tropospheric adjustments to clouds and humidity. Under solar forcing, the reduction in DTR at the first time-step after forcing (-0 .l5DC) was subsequently magnified (-0 .l7DC) by feedbacks. Rapid adjustments were dominated by a reduction in surface sensible heat (-1.39 Wmo2) offset by an inversely correlated increase in surface latent heat (+0.98 Wmo2). There was no evidence of a tropospheric rapid adjustment with solar forcing. CO2 induced diurnal changes in downwelling longwave radiation and rapid adjustments in surface heat fluxes have likely contributed to the global DTR trend. 7 1 I
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available