1998: Evaluation of the Trenberth Mechanism for Displacement of the Jet Stream Pattern During ENSO Events and the Ensuing Weather Anomalies

Researchers: Errol Brown, Mitch Fox, Dorothy Louis, Ron Miller, and Raysa Rodriguez

The ocean team studies the interaction between the atmosphere and ocean. Of particular importance is their combined response to the energy reaching earth from the sun and influence on our climate. This energy is the driving force of global movements (transports and fluxes) of heat, water and momentum resulting in different regional climates. Individual research projects in this group deal with the general characteristics of the ocean such as temperature, salinity and currents. We plan to use this knowledge to understand the long term patterns (climate) and variations from the norm due to climate phenomenon such as El Niño and North Atlantic Oscillation.

Project Goal for 1998-99

Based on earlier research by Trenberth et al, (1996), the Oceans team has hypothesized that the 1997 ENSO, the so-called "El Niño of the Century", should have produced major anomalies in extratropical wind and precipitation patterns to accompany the observed large anomalies in tropical Pacific Sea Surface Temperature (SST). Our preliminary research documents large SST anomalies in the tropical equatorial pacific. When comparing previous ENSO events of the base period 1982-97, we find that the 1997 ENSO is at least comparable to that of 1982-83. We speculated on the strange occurrence of so many tornadoes in anomalous places such as the Carolinas and Virginia. While not totally unheard of in this region, the relative abundance of these events leads us to attempt to correlate them to the ENSO of 1997.

In addition, the period of 13 consecutive days of rainfall in the Northeast and Middle Atlantic States may have also previously occurred but again we hypothesize on the possible relationship to the ENSO. Questions asked include: how well has the GISS Atmospheric General Circulation Model (AGCM) predicted the events for the Fall, Winter, and Spring of 1997-98 time period? Also to be addressed are the teleconnections, if any, between ENSO and the North Atlantic Oscillation (NAO). Is there a connection, and are these phenomena linked to other regions globally? We will try to answer these questions and investigate the AGCM's replication of the real world's connectivity. Establishing these teleconnections can show us areas in the world that we should see good predictability.

Science Questions

1. Are the pressure, wind, and precipitation patterns of the eastern US for the ENSO period (1997-98) anomalous compared to the base period (1982-97)? (Trenberth Mechanism)
2. Are these patterns anomalous when compared to the other ENSOs of the period, such as 1982-83 and 1986-87?
3. Why were the hurricanes of the 1996 season so mild and infrequent?
4. Are the anomalous tornadoes of the Carolinas and Virginia related to the ENSO?
5. Did the AGCM successfully simulate the observed anomalies of 1997-98?
6. Teleconnections, how well are different regions of the atmosphere correlated with each other?

Hypotheses

1. Dr. Trenberth's Mechanism: The Jet Stream which steers our weather is diverted from its normal path by ENSO and sometimes split with a North Polar Jet moving over Canada and a Subtropical Jet carrying moisture to southern California and the Gulf Coast.
2. Dr. Hansen's chaos hypothesis is that the higher latitudes experience weather patterns and climate that is more often the result of the natural chaos of the system and that the weather patterns and climate of the lower latitudes is more often the result of the interplay of deterministic factors. Does the correct answer depend upon whether it is the winter or summer season we are looking at?
3. Dr. Gray's Hurricane Hypothesis: The most damaging hurricanes occur when several factors act in concert to produce the best conditions such as great depth (200 feet)of warm water (80°F), supporting wind circulation from the east at all levels in the atmosphere, many seed disturbances coming from the western coast of Africa near the equator, and supporting upper air high or strong stratospheric Jet from the east (easterly QBO). Does the ENSO somehow interfere with the upper air support necessary for the development of the tropical cyclone?

Research Tasks

1. Calculation of seasonal, annual, and base period SST, SLP, (and Geopotential heights 250 and 500 mb levels) as indicators of wind.
2. Calculation of seasonal and annual anomalies for SST, SLP, and Global Wind Patterns.
3. Production of global distribution charts for anomalies of SST, SLP, and Jet Stream Wind Patterns for the ENSO events of 1982-83, 1986-87, 1997-98.
4. Calculation of ENSO and NAO indices for 1950-97, correlation of those indices with each other plus global SST and SLP.
5. Production of teleconnection maps of the Northern Hemisphere based on model SLP output as well as air pressure at the 300 mbs Geopotential Height.
6. Interpretation of the charts and the creation of annotations for charts.
7. Comparison of the observed data to the model data provided by the AGCM.

Data

The Reynolds _OI_ SST Global Database for the period (1982-97) as well as data for SLP and geopotential heights of the 250, and 500 mb levels which can be prepared in hdf format.

Model

AGCM data for the base period 1982-97 will be used to produce and compare maps of observations to the simulations (predictions) of the AGCM Model A 1997 which will depict SST, SLP, Global Winds and Precipitation Patterns. Runs B295DM12 (climatological SST) and B299AM12 (observed sea ice and SST) will be used to create the teleconnection maps.