No abstract

No abstract

The central Pacific near‐equatorial convergence zone (CZ) lies north of the equator throughout the year. On an average it moves between 4°N in spring and 8°N in autumn, probably in response to annual variation in the strengths of the northeast and southeast trade winds. For 6 weeks in the period November 1977 to January 1978 a NOAA P‐3 research aircraft flew between Hawaii and Tahiti, southward along 150°W and northward along 158°W, at a frequency of one round trip per week. During this time the CZ lay near its climatological latitude. Late season North Pacific and early season South Pacific tropical cyclones caused the CZ to be more variable than usual, especially along 158°W. The aircraft flew at an altitude of 250 m between 11°N and 0.5°S, and the data from these segments of the flights have made possible an examination of the CZ in unprecedented detail. High resolution satellite images, high and low cloud movement vectors, soundings from several island stations, and soundings made by the aircraft while it descended to and ascended from the low‐level segments were all used to determine the large‐ and small‐scale influences on the CZ at the time of each traverse. From the aircraft data time series of selected variables and time‐latitude sections showing variables averaged over 1/4° latitude were plotted. The types of CZ's encountered had several common features and yet were remarkably diverse. Ten s averages revealed that the CZ was almost always clearly delineated by abrupt changes in temperature and humidity. In many cases, convergence and rainfall were greatest at these boundaries while divergence was large somewhere between. Narrow zones with low moist static energy were frequently encountered within the CZ, indicating that a midtropospheric dry layer and compensating sinking existed within the CZ, a region which had been commonly thought to be merely a funnel for moist surface air to be moved to the upper troposphere where the energy of condensation is exported to higher latitudes. Measurements from the gust probe showed that turbulent fluxes of sensible and latent heat were not necessarily greatest in the CZ, implying that the associated sea surface temperature maximum did not regulate the position or intensity of the convergence zone. There are indications that the upper troposphere played an important role. Soundings showed that the trade wind inversion extended to the latitude of the CZ without significant change in height along the trade wind trajectory. The inversion may even extend across the CZ and thus inhibit deep convection. At least in the central Pacific it appears that the CZ may make only a small contribution to the Hadley cell and have little effect on mid‐latitude circulations.

No abstract

No abstract

No abstract

No abstract

No abstract