Über die Autorin bzw. den Autor

Auszug. © Genehmigter Nachdruck. Alle Rechte vorbehalten.

Natural History of the White-Inyo Range, Eastern California

University of California Press

Introduction

The highest range of the many mountain ranges that are arranged en echelon in the Great Basin between the Sierra Nevada and the Wasatch Mountains is the White Mountains, situated along the California-Nevada border about 225 mi (362 km) east of the Pacific Coast. Climatically, this location is transitional between the moderating maritime influence of the Pacific Ocean and the more extreme continental influence of interior North America. The very large variation in elevation within the range, from 4,0005,000 ft (1,2001,500 m) at the base to 14,246 ft (4,343 m) at the summit, results in rapid and significant changes in temperature and precipitation within short horizontal distances. Any air mass reaching the White Mountains must pass over an assemblage of other ranges that vary in width and altitude. By far the most important of these mountain barriers is the equally high Sierra Nevada, lying immediately to the west, which, by inducing air to rise, clouds to form, and precipitation to fall, intercepts some of the moisture from Pacific storms in the winter half of the year. To the north, east, and south are a series of lower ranges that have lesser climatic influence. Topographically, the least impeded avenue of approach for an air mass is from the southeast, but significant movement of air from this direction is uncommon. When it does occur, normally in July or August, the result may be spectacular thunderstorms with high precipitation intensities.

Atmospheric Circulation Patterns

Unlike other features of the physical environment, the gases that constitute the atmosphere are invisible, so that it is necessary to use indirect means to describe graphically and to map continuously changing atmospheric conditions. Atmospheric motions are complex, but when studied they are found to follow patterns. To understand the weather regimes of the White-Inyo mountains, it is helpful to recognize three principal scales of motion, each roughly an order of magnitude greater than the next.

The first and largest of these is the synoptic scale , so called because it is analyzed from numerous soundings, measurements, and observations made at the same time at hundreds of locations around the world. This is the scale of the familiar weather maps seen in daily newspapers and on television. These surface and upper-air charts cover horizontal distances of 100 to 2,000 mi (160 to 3,200 km) and depict such features as low- and high-pressure areas, cyclones, and anticyclones, air masses, weather fronts, and regions of precipitation. Generally, these features progress in a predictable manner,

and from them it is possible to produce, by computerized prediction models, future patterns of airflow, moisture, temperature, clouds, and precipitation. These are used to forecast, with varying degrees of certainty, weather conditions for a particular region for a few days following receipt of the climatic data.

The second scale of atmospheric motion, the mesoscale , describes airflow patterns over distances of, say, 1 to 100 mi (or 1.6 to 150 km), a range that includes many of the spectacular cloud formations and weather conditions experienced in and near the mountains of eastern California (Plates 1.11.8). These phenomena are closely related to the synoptic flow patterns but are controlled and shaped by major terrain features such as the Sierra Nevada and the White-Inyo Range.

The third scale, the toposcale , applies to weather and climatic conditions within a distance of, say, 1 mi (1.6 km) that vary in relation to prominent features shown on local (15-minute or 7.5-minute series) topographic maps. Thus, under differing synoptic and mesoscale conditions different air temperatures, wind velocities, and snow accumulations are measured, whether the location is on a mountain ridge or in a canyon, on a windward or leeward slope, or in a broad valley.

In the sections that follow we discuss the principal patterns that affect the White-Inyo Range, its inhabitants, and its visitors in each of these different scales. We begin with a survey of synoptic-scale airflow and its relation to seasonal weather.

Synoptic-Scale Circulation

Weather Regimes

Figure 1.1 shows the principal airflow patterns and air-mass types or source regions that determine regional weather in different seasons of the year. The arrows indicate the directions of air movement near and above the crest of the major mountain ranges, at levels between 10,000 and 20,000 ft (3 to 6 km) above sea level. The open circles are locations from which twice-daily (near 4 A.M. and 4 P.M. PST) rawinsonde balloon ascents are made to obtain data on air temperature, humidity, and wind velocity, from which upper-air (e.g., 500 mb) weather maps are plotted and analyzed. The black circle indicates the location of the Bishop Airport, the nearest (3 mi, or 5 km) National Weather Service station to the White-Inyo Range.

The air that flows across California at any time of year is most likely to have passed over some part of the Pacific Ocean. In summer the Pacific Anticyclone (a large, slow-moving clockwise whirl of air) lies just west of California, bringing an onshore flow of cool marine air, stratus clouds, and fog to the coast and mostly clear, dry air to the Sierra and White-Inyo Range. During much of the summer the Great Basin Anticyclone develops over the warm plateau region of Nevada and Utah. When this whirl expands and shifts westward, a flow of moist maritime tropical air from the Gulf of California or the Gulf of Mexico may persist for a few days before the normally dry Pacific flow reasserts itself. Thus, during the summer season the mountainous terrain of eastern California and western Nevada is contested for by two air masses, with that from the northern or central Pacific usually prevailing.

Figure 1.1
Major airflow patterns and air mass types affecting California and the Great
Basin. Rawinsonde stations shown are: