The Tropical Rain Belts with an Annual Cycle and Continent Model Intercomparison Project (TRACMIP) ensemble—a multimodel ensemble of slab-ocean simulations in idealized configurations—provides a test of the relationship between the zonal mean ITCZ and the cross-equatorial atmospheric energy transports (AHTeq). In a gross sense, the ITCZ position is linearly related to AHTeq, as expected from the energetic framework. Yet, in many aspects, the TRACMIP model simulations do not conform to the framework. Throughout the annual cycle there are large excursions in the ITCZ position unrelated to changes in the AHTeqand, conversely, substantial variations in the magnitude of the AHTeqwhile the ITCZ is stationary at its northernmost position. Variations both in the net vertical energy input at the ITCZ location and in the vertical profile of ascent play a role in setting the model behavior apart from the conceptual framework. Nevertheless, a linear fit to the ITCZ–AHTeqrelationship captures a substantial fraction of the seasonal variations in these quantities as well as the intermodel or across-climate variations in their annual mean values. The slope of the ITCZ–AHTeqlinear fit for annual mean changes across simulations with different forcings and configurations varies in magnitude and even sign from model to model and we identify variations in the vertical profile of ascent as a key factor. A simple sea surface temperature–based index avoids the complication of changes in the vertical structure of the atmospheric circulation and provides a more reliable diagnostic for the ITCZ position.
Due to its importance for water availability in the tropics and subtropics, efficient tracking of the seasonal and long‐term shifts of the intertropical convergence zone (ITCZ) is of great value. Current approaches, which are based on tracking changes in the annual mean of single variables, ignore the intra‐annual dynamics, while more sophisticated methods are computationally intensive. Here we propose a new probabilistic framework to track the ITCZ, which is based on tracking the location of maximum precipitation and minimum outgoing longwave radiation in overlapping longitudinal windows. Our framework is seasonally and longitudinally explicit, allows for joint consideration of multiple variables to define the ITCZ, and is flexible in its implementation, thus, it can be used in analyses of different scales and scopes. We apply our framework to analyze the recent climatology of the ITCZ and report a southward trend in its location over central Pacific in the late twentieth century.
more » « less- NSF-PAR ID:
- 10374763
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 45
- Issue:
- 23
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Location Global.
Time period Current.
Major taxa studied Turtles.
Methods We gathered distribution, phylogenetic and body size data for 235 species of turtles, which were distributed in a global equal area grid of 200 km × 200 km. We also obtained predictor variables [mean annual temperature, actual evapotranspiration, temperature variation since the Last Glacial Maximum (LGM) and human footprint] directly associated with the main hypotheses tested in body size studies. Our analyses followed a cross‐species and an assemblage‐based approach and were performed for all turtles and for terrestrial and aquatic species separately.
Results Mean annual temperature was the main correlate of body size for the whole group and for terrestrial turtles in both approaches, having a positive correlation with this trait. Body sizes of aquatic turtles were not influenced by any of the tested variables. In the cross‐species approach we also found that temperature variation since the LGM was an important positive correlate of body size in terrestrial turtles.
Main conclusions Our study reinforces the importance of environmental temperatures in explaining animal body size patterns. The heat balance hypothesis was not rejected by our data, whereas migration, productivity and human disturbance hypotheses were rejected. Finally, body size of terrestrial and aquatic turtles had different patterns, also suggesting that habitat is an important factor in understanding geographical variation in body size.
