Examination of historical climate records indicates a significant relation between the El Nin??o/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 Nin??o and La Nin??a 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 Nin??a events), winters with NINO3.4 anomalies > 1??C (El Nin??o 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 Nin??o events primarily affect precipitation characteristics of weather types at New Orleans, whereas the effects of La Nin??a events are most apparent in weather-type frequencies. During El Nin??o events, precipitation for some of the weather types is greater than during neutral and La Nin??a 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 Nin??a events are indicative of a northward shift in storm tracks and/or a decrease in storm frequency in southern Louisiana.
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Effects of ENSO on weather-type frequencies and properties at New Orleans, Louisiana, USA