Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.

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Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present

Statistics for Spatial Data.

From a societal, weather, and climate perspective, precipitation intensity, duration, frequency, and phase are as much of concern as total amounts, as these factors determine the disposition of precipitation once it hits the ground and how much runs off. At the extremes of precipitation incidence are the events that give rise to floods and droughts, whose changes in occurrence and severity have an enormous impact on the environment and society. Hence, advancing understanding and the ability to model and predict the character of precipitation is vital but requires new approaches to examining data and models. Various mechanisms, storms and so forth, exist to bring about precipitation. Because the rate of precipitation, conditional on when it falls, greatly exceeds the rate of replenishment of moisture by surface evaporation, most precipitation comes from moisture already in the atmosphere at the time the storm begins, and transport of moisture by the storm-scale circulation into the storm is vital....

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The Changing Character of Precipitation

An overview of model-based geostatistics.- Gaussian models for geostatistical data.- Generalized linear models for geostatistical data.- Classical parameter estimation.- Spatial prediction.- Bayesian inference.- Geostatistical design.

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Model-based Geostatistics

Global cooling in the Cenozoic, which led to the growth of large continental ice sheets in both hemispheres, may have been caused by the uplift of the Tibetan plateau and the positive feedbacks initiated by this event. In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr.

Tectonic forcing of late Cenozoic climate

A comparison of rain rates retrieved from the Nimbus 5 electronically scanning microwave radiometer brightness temperatures and observed from shipboard radars during the Global Atlantic Tropical Experiment (GATE) phase I shows that the beam filling error is the major source of discrepancy between the two. When averaged over a large scene (the GATE radar array, 400 km in diameter), the beam filling error is quite stable, being 50 percent of the observed rain rate. This suggests the simple procedure of multiplying retrieved rain rates by 2 (correction factor). A statistical model of the beam filling error is developed by envisioning an idealized instrument field-of-view that encompasses an entire gamma distribution of rain rates. A modeled correction factor near 2 is found for rain rate and temperature characteristics consistent with GATE conditions. The statistical model also suggests that the correction factor varies from 1.5 to 2.5 for suppressed to enhanced tropical convective regimes, and decreases to 1.5 as the freezing level and average depth of the rain column decreases to 2.5 km.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JD095iD03p02187%4010.1002/%28ISSN%292169-8996.MESOPRE1

The beam filling error in the Nimbus 5 electronically scanning microwave radiometer observations of Global Atlantic Tropical Experiment rainfall

Atmospheric water vapor content over the global oceans is measured to study the air-sea interactions associated with El Nino/Southern Oscillation. A scanning multichannel microwave radiometer measured brightness temperatures of the earth-atmosphere system at 6.6, 10.7, 18, 21, and 37 GHz, and from these data water vapor content is derived. The seasonal mean distribution of water vapor for the regular season cycle from 1979-1981 are examined; the minima associated with the subtropical anticyclones in the Pacific and Atlantic Oceans in the Northern and Southern hemispheres, and the Walker circulation in the tropical Pacific Ocean are analyzed. The positive and negative anomalies in water vapor during the 1982-1983 El Nino event, which correspond to convergence and enhanced convective activity, are investigated. It is concluded that during El Nino events a system of convection and subsidence exists; the subsidence slows the supply of water vapor and cloud growth in the convectively active center and the Walker circulation is reversed.

El Niño and Atmospheric Water Vapor: Observations from Nimbus 7 SMMR

Atmospheric GCMs have shown that thermally forced monsoon circulations are enhanced by the strengthened seasonal cycle of solar heating that results when summer solstice occurs near perihelion. However, observations indicate that the tropical climatic response reaches a maximum thousands of years after solstice-perihelion alignment. The reasons for this lag are addressed by examining the response to the precession cycle. The model utilized suggests that some features of the monsoon circulation may reach maximum intensity about 3000 yr after solstice-perihelion alignment as the result of a direct thermal response to the astronomical forcing.

Tropical climatic phase lags and earth's precession cycle

A systematic approach is suggested for modeling the probability distribution of rain rate. Rain rate, conditional on rain and averaged over a region, is modeled as a temporally homogeneous diffusion process with appropiate boundary conditions. The approach requires a drift coefficient-conditional average instantaneous rate of change of rain intensity-as well as a diffusion coefficient-the conditional average magnitude of the rate of growth and decay of rain rate about its drift. Under certain assumptions on the drift and diffusion coefficients compatible with rain rate, a new parametric family-containing the lognormal distribution-is obtained for the continuous part of the stationary limit probability distribution. The family is fitted to tropical rainfall from Darwin and Florida, and it is found that the lognormal distribution provides adequate fits as compared with other members of the family and also with the gamma distribution.

A Probability Distribution Model for Rain Rate

Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) measurements at five frequencies in the region 6.6 to 37 GHz, at a resolution of 155 km, are analyzed to infer precipitation over the global oceans. The microwave data show, on this spatial scale, that the combined liquid water in the clouds and rain increases the brightness temperature almost linearly with frequency in the 6.6-18-GHz region, while at 37 GHz such a simple relationship is not noticed. Further, as the atmospheric water-vapor absorption and the effects of scattering by precipitation particles are relatively weak at 6.6 and 10.7 GHz, a technique to remotely sense the liquid water content in the atmosphere is developed based on the brightness measurements at these two frequencies. Seasonal mean patterns of liquid water content in the atmosphere derived from SMMR over global oceans relate closely to climatological patterns of precipitation. Based on this, an empirical relationship is derived to estimate precipitation over the global oceans, with an accuracy of about + or - 30 percent, on a seasonal basis from satellite measurements made during the three years (1979-81) before the recent El Nino event. The deviations from these three-year means, in the precipitation, produced by the 1982-83 el Nino event are then deduced from the SMMR measurements. In the Pacific, the precipitation over the ITCZ in the north, the South Pacific Convergence Zone, and the oceans around Indonesia is drastically reduced. At the same time a substantial increase in precipitation is observed over the normally dry central and eastern equatorial Pacific Ocean.

David A. Short

Papers

The beam filling error in the Nimbus 5 electronically scanning microwave radiometer observations of Global Atlantic Tropical Experiment rainfall

El Niño and Atmospheric Water Vapor: Observations from Nimbus 7 SMMR

Tropical climatic phase lags and earth's precession cycle

A Probability Distribution Model for Rain Rate

Rainfall over oceans inferred from Nimbus 7 SMMR - Application to 1982-83 El Nino