CPC: Climate Assessment for 1994 - Climate and Global Change Issues: Troposphere Temperatures

CPC: Climate Assessment for 1994 -
Climate and Global Change Issues: Troposphere Temperatures

Since 1979 satellite-derived estimates of lower-troposphere temperature have been obtained from measurements taken by the MSU channel 2R flown aboard the NOAA polar-orbiting satellites (Spencer et al. 1990). Interannual variations in global tropospheric temperature primarily reflect the influence of cold and warm episodes in the tropical Pacific and the shading effects resulting from stratospheric aerosols emitted by intense low-latitude volcanic eruptions (Fig. 1.7). Global temperature anomalies (Fig. 1.7a) reached a maximum in late 1987 following the 1986-1987 warm episode, and then reached a minimum in early 1989 following the peak in the 1988-1989 cold episode. Temperatures then increased until mid-1991 as conditions in the tropical Pacific evolved toward the 1991-1993 warm episode. The cooling effects due to the large increase in stratospheric aerosols, which accompanied the eruption of Mt. Pinatubo, are evident in the tropics and in the extratropics of both hemispheres, particularly during the Northern Hemisphere 1992 and 1993 summer seasons (Fig. 1.7c).

During 1994 global temperature anomalies returned to near zero (Fig. 1.7a). In part this is due to a return to near-normal concentrations of stratospheric aerosols but may also reflect a warming due to the development of warm episode conditions in the tropical Pacific during the latter half of the year. The upward trend in global tropospheric temperatures during the last two and a half years is also reflected in the radiosonde-based tropospheric temperature anomalies (Fig. 1.8, top). For 1994 as a whole, the satellite-estimated global temperature anomaly was near zero, while the radiosonde-based estimate of tropospheric mean temperature anomaly for the layer from 850 mb to 300 mb was slightly positive. The difference between the estimates is within the uncertainties resulting from the differences in the instruments, networks, methods of calculating the global mean tropospheric temperatures, and differences in base periods used as references for computing the anomalies.

The spatial patterns of tropospheric temperature anomalies based on satellite estimates (Figs. 1.9 and 1.10) indicate that positive anomalies prevailed over much of the Pacific Ocean during the last five years. 1992 and 1993 were noticeably cooler than 1990 and 1991 especially for northeastern Siberia, the southwestern United States, northeastern Canada, northern Africa, western Asia, and Antarctica. During 1994, positive temperature anomalies prevailed over Europe, eastern Asia and the western Pacific, extreme northern Canada, and central South America. Negative anomalies continued over many sections of Antarctica, Australia, western Asia, and the northern two-thirds of Africa.

Climate and Global Change Issues: Stratosphere Temperatures
Climate and Global Change Issues: Surface Temperatures
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