Effects of ENSO on weather-type frequencies and properties at New Orleans, Louisiana, USA

Abstract

Examination of historical climate records indicates a significant relation between the El Niño/Southern Oscillation (ENSO) and seasonal temperature and precipitation in Louisiana. In this study, a 40 yr record of twice daily (06:00 and 15:00 h local time) weather types are used to study the effects of ENSO variability on the local climate at New Orleans, Louisiana. Tropical Pacific sea-surface temperatures (SSTs) for the NINO3.4 region are used to define ENSO events (i.e. El Niño and La Niña events), and daily precipitation and temperature data for New Orleans are used to define weather-type precipitation and temperature properties. Data for winters (December through February) 1962-2000 are analyzed. The 39 winters are divided into 3 categories; winters with NINO3.4 SST anomalies < -1°C (La Niña events), winters with NINO3.4 anomalies > 1°C (El Niño events), and neutral conditions (all other years). For each category, weather-type frequencies and properties (i.e. precipitation and temperature) are determined and analyzed. Results indicate that El Niño events primarily affect precipitation characteristics of weather types at New Orleans, whereas the effects of La Niña events are most apparent in weather-type frequencies. During El Niño events, precipitation for some of the weather types is greater than during neutral and La Niña conditions and is related to increased water vapor transport from the Tropics to the Gulf of Mexico. The changes in weather-type frequencies during La Niña events are indicative of a northward shift in storm tracks and/or a decrease in storm frequency in southern Louisiana.