An investigation of the potential of the high-resolution dynamics limb sounder for upper tropospheric and lower stratospheric ozone and water vapour measurements: a minimum performance scenario Original Research Article

A challenge for the next generation of satellite instruments is to observe the upper troposphere and lower stratosphere. Amongst the many species of significance, ozone and water vapour in the upper troposphere present particular problems due to steep gradients in mixing ratio at the tropopause. The High Resolution Dynamics Limb Sounder (HIRDLS), due to fly on EOS-CHEM in 2003, will observe this atmospheric region with a number of radiometer channels. For both ozone and water vapour, HIRDLS will employ multiple channels to measure their emission signals and will simultaneously determine temperature to a precision of 0.4 K from carbon dioxide radiometers. In this paper, a minimum performance scenario for HIRDLS is examined in which only single ozone and water vapour channels, and a temperature precision of 1.5–2.0 K, are available; the temperature precision adopted is commensurate with performance achieved by instruments on the Upper Atmosphere Research Satellite (UARS). The ozone and water vapour channels at 8.85 μm and 7.09 μm respectively are simulated. Optimal estimation is employed in vector form thus providing averaging kernels which indicate the likely vertical resolution of the measurements. It is shown that even in this degraded performance scenario, HIRDLS should be capable of measuring well into the troposphere with precisions of better than 30% away from the tropical tropopause.