Search Results

You are looking at 1 - 10 of 43 items for

  • Author or Editor: A. J. MITCHELL x
  • Refine by Access: All Content x
Clear All Modify Search
A. J. MITCHELL

Abstract

No Abstract Available.

Full access
A. J. MITCHELL

SYNOPSIS

This paper describes Lake Okeechobee as to area, depth, configuration, drainage area, and other features, particularly with reference to the hurricane disasters of 1926 and 1928.

Lake Okeechobee is in the south-central portion of the Florida peninsula; it is between 30 and 40 miles in diameter. The surface of the lake is between 700 and 800 square miles; its depth varies from a maximum of 15 feet to only a few inches at the outer circumference, especially on the south and west shores where the water is shallow. The configuration of the lake is nearly round, and its drainage area comprises 5,300 square miles. The Everglades, an area about 90 miles long and 40 miles wide, compose an area of 4,500 square miles; they are just to the south of the lake and over which shore (south) the flood waters of Lake Okeechobee found their exit to a large extent. It was to drain these glades that inspired the first efforts of Gov. N. B. Broward in seeking a platform in race for governor. Broward made the race on “Draining the Everglades,” which platform carried him into the State's executive chair, and later to the very door of the United States Senate, but a cruel fate decreed that he should not enter; he died before he took his seat.

I have, thus, termed the Lake Okeechobee and Everglades project: An industrial baby, born of a political exigency.

Progress now being made to offset the dreadful incidents which have attended tropical storms in the Okeechobee region during the last few years should prove reassuring to many who have property and other interests in the Everglades district. The State of Florida and the Federal Government are constructing levees on and around the lake to the end that disasters such as those that attended the hurricanes of 1926 and 1928 shall not recur.

Full access
A. J. MITCHELL

Abstract

No Abstract Available.

Full access
A. J. MITCHELL

Abstract

No Abstract Available.

Full access
A. J. MITCHELL

Abstract

No Abstract Available.

Full access
J. A. Mitchell
and
Raphael Zon
Full access
David A. Rahn
and
Christopher J. Mitchell

Abstract

Observations from commercial aircraft [e.g., the Aircraft Meteorological Data Relay (AMDAR) automated weather reports] have been increasing dramatically. Two main applications of the aircraft data are use in short-term forecasts and assimilation into numerical weather prediction models. Now that more than 10 years of measurements exist, using this dataset to construct a description of the long-term climatological behavior (a “climatology”) of the lower atmosphere is explored with two main objectives. The first objective is to examine strengths and weaknesses of using the dataset to construct a climatology of the lower atmosphere. Unlike the traditional twice-daily radiosonde launches, the high frequency of observations at major airports allows for an unprecedented set of diurnal information at many locations globally. The second objective is to obtain a climatology of the lower atmosphere of Southern California, specifically at Los Angeles, San Diego, and Ontario, during the spring and summer when the boundary layer is well defined and easily detected. The June 2001–14 climatology reveals that the deepening of the boundary layer overnight is consistent with a cloud-topped boundary layer. Whereas the average boundary layer height decreases right after sunrise at San Diego, at Los Angeles the deeper boundary layer persists about 4 h after sunrise and then decreases rapidly over 2 h as the onshore sea breeze strengthens. Morning intrusions of the marine air inland are easily detected at Ontario in some months but are practically nonexistent during July and August.

Full access
C. A. Senior
and
J. F. B. Mitchell

Abstract

The importance of the representation of cloud in a general circulation model is investigated by utilizing four different parameterization schemes for layer cloud in a low-resolution version of the general circulation model at the Hadley Centre for Climate Prediction and Research at the United Kingdom Meteorological Office. The performance of each version of the model in terms of cloud and radiation is assessed in relation to satellite data from the Earth Radiation Budget Experiment (ERBE). Schemes that include a prognostic cloud water variable show some improvement on those with relative humidity-dependent cloud, but all still show marked differences from the ERBE data. The sensitivity of each of the versions of the model to a doubling of atmospheric C02 is investigated. Midlevel and lower-level clouds decrease when cloud is dependent on relative humidity, and this constitutes a strong positive feedback. When interactive cloud water is included, however, this effect is almost entirely compensated for by a negative feedback from the change of phase of cloud water from ice to water. Additional negative feedbacks are found when interactive radiative properties of cloud are included and these lead to an overall negative cloud feedback. The global warming produced with the four models then ranges from 5.4° with a relative humidity scheme to 1.9°C with interactive cloud water and radiative properties. Improving the treatment of ice cloud based on observations increases the model's sensitivity slightly to 2.1°C. Using an energy balance model, it is estimated that the climate sensitivity using the relative humidity scheme along with the negative feedback from cloud radiative properties would be 2.8°C. Thus, 2.8°–2.1°C appears to be a better estimate of the range of equilibrium response to a doubling Of C02.

Full access
J. M. Gregory
,
J. F. B. Mitchell
, and
A. J. Brady

Abstract

A time-dependent climate-change experiment with a coupled ocean–atmosphere general circulation model has been used to study changes in the occurrence of drought in summer in southern Europe and central North America. In both regions, precipitation and soil moisture are reduced in a climate of greater atmospheric carbon dioxide. A detailed investigation of the hydrology of the model shows that the drying of the soil comes about through an increase in evaporation in winter and spring, caused by higher temperatures and reduced snow cover, and a decrease in the net input of water in summer. Evaporation is reduced in summer because of the drier soil, but the reduction in precipitation is larger. Three extreme statistics are used to define drought, namely the frequency of low summer precipitation, the occurrence of long dry spells, and the probability of dry soil. The last of these is arguably of the greatest practical importance, but since it is based on soil moisture, of which there are very few observations, the authors’ simulation of it has the least confidence. Furthermore, long time series for daily observed precipitation are not readily available from a sufficient number of stations to enable a thorough evaluation of the model simulation, especially for the frequency of long dry spells, and this increases the systematic uncertainty of the model predictions. All three drought statistics show marked increases owing to the sensitivity of extreme statistics to changes in their distributions. However, the greater likelihood of long dry spells is caused by a tendency in the character of daily rainfall toward fewer events, rather than by the reduction in mean precipitation. The results should not be taken as firm predictions because extreme statistics for small regions cannot be calculated reliably from the output of the current generation of GCMs, but they point to the possibility of large increases in the severity of drought conditions as a consequence of climate change caused by increased CO2.

Full access
K. D. Williams
,
C. A. Senior
, and
J. F. B. Mitchell

Abstract

A comparison of the response to increasing greenhouse gas concentrations of two versions of the Met Office's (Hadley Centre) coupled atmosphere–ocean model reveals differences that result in large local variations in the modeled impact of climate change. With the aim of understanding the important processes and feedbacks associated with climate change, and ultimately reducing uncertainty in predictions, a series of sensitivity experiments were performed using a coupled atmosphere–mixed layer ocean model. The primary differences in the atmospheric response of the coupled models studied are found to be due to changes made to the physical representation of the atmosphere rather than to the ocean. In particular, many of the different patterns of response can be explained through changes made to the boundary layer scheme combining in a nonlinear way with changes to the cloud scheme to alter the tropical temperature and precipitation response in the model. A new land surface exchange scheme largely accounts for the different Northern Hemisphere continental surface temperature response.

Full access