Tropical waves, instabilities and ITCZ: A perspective from the early days of Jim Holton and now

In the 1960s, a relatively small amount of rawinsonde data from tropical stations were exploited in clever ways to deduce properties of tropical wave propagation in the troposphere and lower stratosphere -- deductions which have stood the test of time remarkably well and have been confirmed in the modern era with a torrent of satellite and global analysis data. Perhaps equally remarkable is that -- despite the passage of time and acquisition of new data -- little progress has been made on some of the most fundamental issues in tropical dynamical meteorology: viz., questions pertaining to the interaction of moist tropical waves, instabilities and Inter-Tropical Convergence Zone (ITCZ). This stagnation is one reason why global climate models have had such difficulty in simulating the ITCZ. Our talk will review (i) the early discoveries, (ii) the unique and relatively little-known contributions of Jim Holton to the subject, (iii) how Jim's thinking was influenced by these discoveries and (iv) what influence, if any, his contributions may have had at the time, and in later years. Since many of the issues raised by his work remain open, it is likely that a fresh perspective on the interaction of tropical waves and ITCZ will arise from (among other things) a renewed appreciation of the issues as seen through Jim's eyes. Considerable progress is likely to be achieved in the coming years as a vast collection of satellite data and imagery, together with high-resolution analyses, are integrated into a coherent study, guided by theoretical considerations. To the extent that modelers wish to simulate reality, this progress will be valuable for an improved understanding of tropical weather and climate and their effects on human life and property.