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FROM VOLUME 9, NUMBER 9, SEPTEMBER 1996

PROFESSIONAL PUBLICATIONS...
TREND ANALYSIS: ATMOSPHERIC PROPERTIES

Item #d96sep61

"Widespread Increases in Low-Frequency Variability of Precipitation over the Past Century," A.A. Tsonis (Dept. Geosci., Univ. Wisconsin, Milwaukee WI 53201), Nature, 382(6593), 700-702, Aug. 22, 1996.

Examines the nature of time fluctuations in several global data sets of precipitation. Finds that the global mean precipitation has not changed, in agreement with other analyses, but fluctuations about the mean have increased significantly on decadal to multi-decadal time scales. Over the past century—during which climate warming has occurred—fluctuations on those time scales have made extremes more probable. This result is consistent with predictions from model simulations of global climate-warming scenarios.

Item #d96sep62

"Downward Trends in the Frequency of Intense Atlantic Hurricanes During the Past Five Decades," C.W. Landsea (Clim. & Global Change, NOAA AOML/Hurricane Res. Div., 4301 Rickenbacker Causeway, Miami FL 33149; e-mail: landsea@aoml.noaa.gov), N. Nicholls et al., Geophys. Res. Lett., 23(13), 1697-1700, June 15, 1996.

Contrary to the expectation of many that tropical cyclones may be developing more frequently due to greenhouse gases, the Atlantic basin has in recent decades seen a significant trend of fewer intense hurricanes and weaker cyclones overall. In addition, the maximum intensity reached in each year has shown no appreciable change. However, 1995 has at least temporarily heralded the return of Atlantic basin hurricanes. Several years must pass before we will know if this marks the beginning of a new regime of active hurricanes.

Item #d96sep63

"Wadati Conference on Global Change and the Polar Climate, 7-10 November 1995, Tsukuba, Japan," J.E. Walsh (Dept. Atmos. Sci., Univ. Illinois, 102 Atmos. Sci. Bldg., 105 S. Gregory Ave., Urbana IL 61801), H.L. Tanaka, G. Weller, Bull. Amer. Meteor. Soc., 77(6), 1268-1273, June 1996.

A recurring theme of the conference was the possibility of an abrupt and surprising climate change involving the high latitudes. Recent results of climate models suggest that the enhanced greenhouse effect should be detectable in the polar regions and elsewhere in the next decade or two. This conference highlighted possible early indications of anthropogenic changes and called attention to the need to monitor the polar climate system carefully for rapid, complex, and perhaps surprising changes in the near future.

Item #d96sep64

"Recent Trends in Rain Gauge Precipitation Measurements from the Tropical Pacific: Evidence for an Enhanced Hydrologic Cycle," M.L. Morrissey (Oklahoma Clim. Survey, 1210 Sarkeys Energy Ctr., Norman OK 73019; e-mail: mmorriss@uoknor.edu), N.E. Graham, ibid., 1207-1219.

Analysis of recently compiled rain gauge measurements shows a trend towards increasing precipitation in the central tropical Pacific during the period 1971-1990. The data corroborate previous results based on satellite measurements, shipboard observations, and numerical models. The result is also consistent with suggestions that an enhancement of the tropical hydrologic cycle has been responsible for the increase in globally averaged tropospheric temperature during the past two decades.

Item #d96sep65

"Recent Decreases in Arctic Summer Ice Cover and Linkages to Atmospheric Circulation Anomalies," J.A. Maslanik (Ctr. for Astrodynamics Res., CB431, Univ. Colorado, Boulder CO 80309; e-mail: jimm@northwind. colorado.edu), M.C. Serreze, R.G. Barry Geophys. Res. Lett., 23(13), 1677-1680, June 15, 1996.

The net trend in Arctic Ocean sea ice, assumed to be a sensitive indicator of climatic conditions, was -0.6% per year from November 1978 through December 1995. Linkages are proposed between this trend and a sharp increase since 1989 in the frequency of low pressure systems over the central Arctic. The sensitivity of ice cover to regional atmosphere-ice interactions points to the need for sophisticated treatment of sea ice in climate models.

Item #d96sep66

Two items in J. Clim., 9(6), June 1996:

"Evaluation of Long-Term Changes in Radiation, Cloudiness and Surface Temperature on the Territory of the Former Soviet Union," G.M. Abakumova, . .V. Russak (Inst. Astrophys., Estonian Acad. Sci., EE2444 Toravere, Estonia; e-mail: russak@aai.ee) et al., 1319-1327. A statistically significantly decrease has been found in 60% of the time series of global radiation annual totals obtained from 160 actinometric stations. Increased cloudiness and atmospheric turbidity are evaluated as the main causes of the trend. Comparison of stations in rural and urban settings illustrates the influence of urban air pollution on radiation transfer in the atmosphere, as well as on cloudiness and air temperature.

"Intrannual Variability in Reconstructed Canadian Snow Cover, 1915-1992," R.D. Brown (Atmos. Environ. Serv., 2121 Trans Canada Hwy., Dorval PQ H9P 1J3, Can.), B.E. Goodison, 1299-1318. Seasonal snow cover information for southern Canada was reconstructed from daily snowfall and maximum temperature data using a simple mass balance approach. There was no evidence of statistically significantly long-term trends in snow cover in any of the regions, but the data suggested that winter (Dec.-Feb.) snow cover had increased and spring snow cover had decreased over much of the area. The influence of teleconnection patterns was investigated.

Item #d96sep67

"Archival Photographs Show No Climate-Induced Changes in Woody Vegetation in the Sudan, 1943-1994," W.E. Schlesinger (Dept. Botany, Duke Univ., Durham NC 27708; e-mail: schlesin@acpub.duke.edu), N. Gramenopoulos, Global Change Biology, 2(2), 137-141, Apr. 1996.

Woody plants are often better indicators than grasses of long-term climate shifts in arid regions because they are buffered against short-term fluctuations by their deep root systems. This study examines data held in classified intelligence archives to determine trends in the distribution of woody plants in western Sudan. Despite several decades of recent drought, there is no significant evidence of a trend.

Item #d96sep68

"Trends in the Intensity and Frequency of Heavy Rainfall in Tropical Australia and Links with the Southern Oscillation," R. Suppiah (Div. Atmos. Res., CSIRO, PMB 1, Aspendale, Vic. 3195, Australia), K.J. Hennessy, Aust. Meteor. Mag., 45(1), 1-17, Mar. 1996.

Daily rainfall data between September and April from 53 stations were examined for the period 1910 to 1989. Increasing trends in the 90th and 95th percentile rainfall intensity and frequency occur at most stations, but few are statistically significant. Relationships between the Southern Oscillation Index and these heavy rainfall parameters were stronger during 1950-1989 relative to 1910-1949, suggesting a change in large-scale atmospheric circulation patterns.