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 Nino/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 Nino and La Nina 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 Febru- ary) 1962-2000 are analyzed. The 39 winters are divided into 3 categories; winters with NINO3.4 SST anomalies 1°C (El Nino events), and neu- tral conditions (all other years). For each category, weather-type frequencies and properties (i.e. pre- cipitation and temperature) are determined and analyzed. Results indicate that El Nino events pri- marily affect precipitation characteristics of weather types at New Orleans, whereas the effects of La Nina events are most apparent in weather-type frequencies. During El Nino events, precipitation for some of the weather types is greater than during neutral and La Nina 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 Nina events are indicative of a northward shift in storm tracks and/or a decrease in storm frequency in southern Louisiana.