Publications Published in Climate Dynamics

1. A precipitation-dominated, mid-latitude glacier system: Mount Shasta, California. Howat, Ian; Tulaczyk, Slawek; Rhodes, Philip; Israel, Kevin; Snyder, Mark.
   Climate Dynamics: 2007
   Notes
   Temperature is often seen as the dominant control on inter-decadal glacier volume changes. However, despite regional warming over the past half-century, the glaciers of Mount Shasta have continued to expand following a contraction during a prolonged drought in the early twentieth century, indicating a greater sensitivity to precipitation than temperature. We use the 110 year record of fluctuations in Mount Shasta’s glaciers and climate to calibrate numerical glacier models of the two largest glaciers. The reconstructed balance and volume histories show a much greater correlation to precipitation than temperature and significant correlation to oscillatory modes of Pacific Ocean climate. An approximately 20% increase in precipitation is needed for every 1C increase in temperature to maintain stability. Under continued historical trends, oscillations in climate modes and random variability will dominate inter-decadal variability in ice volume. Under the strong warming trend predicted by a regional climate model, the temperature trend will be the dominant forcing resulting in near total loss of Mount Shasta’s glaciers by the end of the twenty-first century.
   
   
   
2. Atmosphere-land cover feedbacks alter the response of surface temperature to CO2 forcing in the western United States. Diffenbaugh, Noah S..
   Climate Dynamics: 2005
   Notes
   Abstract In order to test the sensitivity of regional climate to regional-scale atmosphere-land cover feedbacks, we have employed a regional climate model asynchronously coupled to an equilibrium vegetation model, focusing on the western United States as a case study. CO2-induced atmosphere-land cover feedbacks resulted in statistically significant seasonal temperature changes of up to 3.5 C, with land cover change accounting for up to 60% of the total seasonal response to elevated atmospheric CO2 levels. In many areas, such as the Great Basin, albedo acted as the primary control on changes insurface temperature. Along the central coast of California, soil moisture effects magnified the temperature response in JJA and SON, with negative surface soil moisture anomalies accompanied by negative evaporation anomalies, decreasing latent heat flux and further increasing surface temperature. Additionally, negative temperature anomalies were calculated at high elevation in California and Oregon in DJF, MAM and SON, indicating that future warming of these sensitive areas could be mitigated by changes in vegetation distribution and an associated muting of winter snowtemperature feedbacks. Precipitation anomalies were almost universally not statistically significant, and very little change in mean seasonal atmospheric circulation occurred in response to atmosphere-land cover feedbacks. Further, the mean regional temperature sensitivity to regional-scale land cover feedbacks did not exceed the large- scale sensitivity calculated elsewhere, indicating that spatial heterogeneity does not introduce non-linearities in the response of regional climate to CO2-induced atmosphere-land cover feedbacks.
   
   
   
3. Factors contributing to diurnal temperature range trends in twentieth and twenty-first century simulations of the CCCma coupled model. Stone, D A; Weaver, A J.
   Climate Dynamics: 2003
   Notes
   Trends in the diurnal temperature range (DTR) are examined in the late twentieth and the twenty-first centuries in a coupled climate model representing the atmosphere, ocean, sea ice, and land surface systems. Consistent with past studies, the DTR decreases during this time. These decreases are concentrated in middle latitudes, with much smaller changes occurring in the low latitudes. Strong seasonal characteristics to this pattern exist, although these are different in either hemisphere. In the model integrations, variations in the DTR are much more sensitive to changes in feedbacks than in direct forcings. The DTR is found to be insensitive to the scattering of sunlight by sulfate aerosols and the increased mean temperature. Instead, variations in the DTR arise mostly from changes in clouds and in soil moisture. Consequently, the decreasing trends stem from increases in the reflection of solar radiation by clouds moderated by decreases in soil moisture, mostly through its effect on the ground heat capacity. Both factors contribute about equally to the DTR trend. The exception to this relation occurs in the middle latitudes during winter, when snow cover reduces the influence of changes in solar radiation and soil moisture. Decreases during this season are a consequence of the artificial tendency in the model for the DTR to be very small when the mean temperature is near the freezing point. While the accuracy of these conclusions depends upon the model's ability to represent the relevant processes, the results highlight the importance of clouds and land surface processes to the DTR and its long-term change. The importance of soil moisture found here implies that changes in the physiological response of vegetation and in land use could have important effects on the DTR.
   
   
   
4. Parallel climate model (PCM) control and transient simulations. Washington, W.M.; Weatherly, J W; Meehl, G.A.; Semtner, A J; Bettge, T W; Craig, A P; Strand, W G; Arblaster, J; Wayland, V B; James, R; Zhang, Y.
   Climate Dynamics: 2000
   
   
5. Regional temperature response due to indirect sulfate aerosol forcing: impact of model resolution. Ekman, A. M. L.; Rodhe, H..
   Climate Dynamics: 2003
   Notes
   A regional atmospheric climate model, including an interactive module of the tropospheric sulfur cycle, has been used to conduct yearlong equilibrium simulations of the temperature response due to anthropogenic sulfate aerosol forcing on cloud albedo. A main purpose is to examine differences in the magnitudes as well as patterns of forcing and response between simulations conducted with high (0.4degrees x 0.4degrees, HR) and low (2.0degrees x 2.0degrees, LR)spatial resolutions. Averaged over the model domain, the annual mean indirect forcing differs by only 7% between HR and LR and there is no difference in the annual mean temperature response. The results thus indicate that it is not important to represent small-scale variability (less than or equal to 2.8degrees) when the average indirect climate effect over Europe is considered. However, a notable difference in the geographical distributions of forcing and response is obtained when different resolutions are employed.
   
   
   
6. Secular variability of ENSO events in a 1000-year climatic simulation. Hunt, B. G.; Elliott, T. I..
   Climate Dynamics: 2003
   Notes
   The CSIRO Mark 2 coupled global climatic model has been used to generate 1000 years of simulated climatic variability corresponding to present climatic conditions. A small climatic drift was noted during the simulation. and all results presented are based on detrended conditions. The emphasis here is on El Nino/Southern Oscillation (ENSO) events and their secular variability during the simulation. A number of features of the simulated ENSO climatology are presented and compared with observations. These demonstrate that the model reproduced the major characteristics of observed ENSO variability. A variety of analyses is given to illustrate secular variability of ENSO-related climate. Thus, while the simulated Southern Oscillation is shown to be a robust feature of the model climatology, decadal and oscillatory time variations occurred. Time-smoothing of the Southern Oscillation Index revealed underlying multi-decadal episodes, with associated climatic anomalies.
   
   
   
7. The impact of new physical parametrizations in the Hadley Centre climate model: HadAM3. Pope, V D; Gallani, M L; Rowntree, P R; Stratton, R A.
   Climate Dynamics: 2000
   Notes
   Abstract Results are presented from the latest version of the Hadley Centre climate model, HadAM3 (Hadley Centre Atmospheric Model version 3). It represents a significant improvement over the previous version, HadAM2b. This is demonstrated using a series of ten year integrations with AMIP (Atmospheric Model Intercomparison Project) boundary conditions. The work covers three aspects of model performance: (1) it shows the improvements in the mean climate in changing from HadAM2b to HadAM3; (2) it demonstrates that the model now compares well with observations and (3) it isolates the impacts of new physical parametrizations.
   
   
   
8. The internal climate variability of HadCM3, a version of the Hadley Centre coupled model without flux adjustments. Collins, M.; Tett, S. F. B.; Cooper, C..
   Climate Dynamics: 2001
   Notes
   We examine the internal climate variability of a 1000 year long integration of the third version of the Hadley Centre coupled model (HadCM3). The model requires no flux adjustment, needs no spin up procedure prior to coupling and has a stable climate in the global mean. The principal aims are (I) to validate the internal climate variability against observed climate variability, (2) to examine the model for any periodic modes of variability, (3) to use the model estimate of internal climate variability to asses the probability of occurrence of observed trends in climate variables, and (4) to compare HadCM3 with the previous version of the Hadley Centre model, HadCM2. The magnitude and frequency characteristics of the variability of the global mean surface temperature of HadCM3 on annual to decadal time scales is in good agreement with the observations.