Diurnal precipitation regimes in the global tropics

Diurnal variations of the global tropical precipitation are documented by using two complementary Tropical Rainfall Measuring Mission (TRMM) datasets (3B42 and 3G68) for 1998–2006 in an attempt to provide a unified view of the diurnal cycle and a metric for evaluating numerical model performance. The 3B42 data have better spatial coverage; the 3G68 data offer more accurate diurnal phase information. The first and second empirical orthogonal function (EOF) modes represent the diurnal cycle and account for 89 % of the total variance in 3B42. The third and fourth EOF modes, which account for 10 % of the total variance, represent the semidiurnal cycle. Both datasets yield consistent spatial structures and temporal evolution, but they have different advantages: the patterns derived from 3B42 exhibit less noise, while 3G68 yields an arguably more accurate diurnal phase. The diurnal phase derived from 3G68 systematically leads 3B42 by about 3 h. Three tropical diurnal cycle regimes (oceanic, continental, and coastal) are identified according to the amplitude, peak time, and phase propagation characteristics of the diurnal precipitation. The oceanic regime is characterized by moderate amplitude and an early morning peak [0600–0900 Local Solar Time (LST)], found primarily in the oceanic convergence zones in the Pacific, Atlantic, and Indian Oceans. I