Fig. 114—Typical afternoon cloud composition at Santa Ana during the dry season.
Fig. 115—Temperature curve for Abancay drawn from data obtained by hourly readings on September 27, 1911. Dry bulb readings are shown by a heavy solid line, wet bulb readings by a dotted line. The heavy broken line shows the normal curve when the sky is unobscured by cloud. The reduction in temperature with cloud is very marked.
| FREQUENCY OF DIURNAL VARIABILITY AT COCHABAMBA, 1906 | ||||||||||||||
| Degrees F. | J. | F. | M. | A. | M. | J. | J. | A. | S. | O. | N. | D. | Total No. of days | |
| 0 | 1 | 3 | 10 | 12 | 6 | 10 | 9 | 6 | 9 | 6 | 3 | 4 | 79 | |
| 0-1 | 5 | — | 3 | 5 | 3 | 3 | — | 4 | — | 3 | 1 | 1 | 28 | |
| 1-2 | 10 | 10 | 13 | 11 | 15 | 7 | 14 | 11 | 15 | 10 | 14 | 13 | 143 | |
| 2-3 | 7 | 11 | 3 | 1 | 5 | 8 | 7 | 4 | 3 | 6 | 7 | 6 | 68 | |
| 3-4 | 6 | 2 | 2 | 1 | 2 | 2 | 1 | 6 | 3 | 4 | 3 | 5 | 37 | |
| 4-5 | — | — | — | — | — | — | — | — | — | 1 | 1 | 1 | 3 | |
| Over 5 | 2 | 2 | — | — | — | — | — | — | — | 1 | 1 | 1 | 7 | |
A series of curves shows the daily march of temperature at various locations along the seventy-third meridian. Figs. 109 to 113 are for the Urubamba Valley. Respectively they relate to Pongo de Mainique, 1,200 feet elevation (365 m.), the gateway to the eastern plains; Yavero, 1,600 feet (488 m.), where the tributary of this name enters the main stream; Santo Anato, 1,900 feet (580 m.); Sahuayaco, 2,400 feet (731 m.), and Santa Ana, 3,400 feet (1,036 m.), one of the outposts of civilization beyond the Eastern Cordillera. The meteorological conditions shown are all on the same order. They are typical of dry season weather on the dry floor of a montaña valley. The smooth curves of clear days are marked by high mid-day temperatures and great diurnal range. Santo Anato is a particularly good illustration: the range for the 24 hours is 38° F. (21.1° C.). This site, too, is remarkable as one of the most unhealthful of the entire valley. The walls of the valley here make a sharp turn and free ventilation of the valley is obstructed. During the wet season tertian fever prevails to a degree little known east of the Cordillera, though notorious enough in the deep valleys of the plateau. The curves show relative humidity falling to a very low minimum on clear days. At Santo Anato and Santa Ana, for example, it drops below 30 per cent during the heat of the day. Afternoon cloudiness, however, is a common feature even of the dry season. A typical afternoon cloud formation is shown in [114] . The effect on temperature is most marked. It is well shown in the curve for August 20 and 22 at Yavero. Cloudiness and precipitation increase during the summer months. At Santa Ana the rainfall for the year 1894-95 amounted to 50 inches, of which 60 per cent fell between December and March. For a discussion of topographic features that have some highly interesting climatic effects in the eastern valleys of Peru see Chapter VI.