WE AGREE WITH C.A. MEARS AND F.J. WENTZ ("The effect of diurnal correction on satellite-derived lower tropospheric temperature," Reports, 2 Sept., p. 1548; published online 11 Aug.) that our University of Alabama in Huntsville (UAH) method of calculating a diurnal correction to our lower tropospheric (LT) temperature data (v5.1) introduced a spurious component. We are grateful that they spotted the error and have made the necessary adjustments. The new UAH LT trend (v5.2, December 1978 to July 2005) is +0.123 K/decade, or +0.035 K/decade warmer than v5.1. This adjustment is within our previously published error margin of [+ or -] 0.05 K/decade (1).

We agree with S. C. Sherwood et al. ("Radiosonde daytime biases and late-20th century warming" Reports, 2 Sept., p. 1556; published online 11 Aug.) that there are significant, progressively colder biases in stratospheric radiosonde data, as we and others have noted (1, 2). We further agree that many daytime radiosondes are plagued by spurious cooling in the troposphere as well (3). However, there are also instances in which spurious warming occurs in both day and night soundings. Such a circumstance is not properly accommodated by the day-minus-night (DMN) procedure, a possibility mentioned by Sherwood et al. but not specifically addressed. For example, when the Australian/New Zealand network, prominent in the Southern Hemisphere in Sherwood et al.'s Report, switched instrumentation from Mark III to Vaisala RS-80, both day and night warmed approximately 0.4 K [(3), updated], with tropospheric night readings warming more than day readings. On the basis of this relative difference, the DMN method assumes that a correction for spurious cooling should be applied, when in fact the real error is large and of the opposite sign.

DMN values are useful indicators for pointing out radiosonde changes, but they are often...