Phil J. Englehart

Defining Intraseasonal Rainfall Variability within the North American Monsoon

Abstract This study provides an empirical description of intraseasonal rainfall variability within the North American monsoon (NAM) region. Applying particular definitions to historical daily rainfall observations, it demonstrates that distinct intraseasonal rainfall modes exist and that these modes differ considerably from the monsoon core region in northwest Sonora (SON), California, to its northward extension in southeast Arizona (AZ). To characterize intraseasonal rainfall variability (ISV), separate P-mode principal component (PC) analyses were performed for SON and AZ. The results indicate that in each area, much of the ISV in rainfall can be described by three orthogonal modes. The correlations between ISV modes and total seasonal rainfall reinforce the notion of differing behaviors between the monsoon’s core and extension. For SON all three ISV modes exhibit significant correlation with seasonal rainfall, with the strongest relationship in evidence for the ISV mode, which is related to rainfall in...

Assessing Warm Season Drought Episodes in the Central United States

Abstract Recurrent drought episodes are a signature feature of the climate of the central United States. Using a particular set of definitions, this study examines some of the basic statistical features of previous drought episodes. It shows that there are distinct intraseasonal preferences for the onset of long periods of dry weather and that these preferences vary regionally in ways that are consistent with seasonal climate controls. Evaluation of past drought occurrences indicates that there is no simple or strong teleconnection between drought and the El Nino–Southern Oscillation (ENSO) phenomenon. Individual drought episodes certainly evolve with unique character. However, based on analysis of large-scale variations in sea level pressure patterns, evidence is presented for systematic links between drought and the interdecadal climate mode often referred to as the Pacific decadal oscillation (PDO).

Dissecting the Macro-scale Variations in Mexican Maize Yields (1961-1997)

This paper offers a macro-scale view of maize production in Mexico. It provides the quantitative association between interannual variability in maize yield and fluctuations in seasonal rainfall. It also highlights trends in production variables, and shows that significant trends are present in many of Mexicos state-level rainfall series. The study presents a three-variable model relating yield to rainfall variations. Analysis of model residuals indicates a tendency for nonrandom serial behavior, particularly in the 1990s where the model consistently underestimates yield. This result is consistent with the major geographic shift in maize cultivation from the traditional, rain-fed production core to states in the Northwest. Here, maize production is largely irrigated so that yields presumably are less sensitive to climate fluctuations.