El Niño Dynamics

Bringer of storms and droughts, the El Niño∕Southern Oscillation results from the complex, sometimes chaotic interplay of ocean and atmosphere

El Niño Dynamics

Bringer of storms and droughts, the El Niño∕Southern Oscillation results from the complex, sometimes chaotic interplay of ocean and atmosphere

Dynamics of Decadal Climate Variability and Implications for its Prediction

The temperature record of the last 150 years is characterized by a long-term warming trend, with strong multidecadal variability superimposed. The multidecadal variability is also seen in other (societal important) parameters such as Sahel rainfall or Atlantic hurricane activity. The existence of the multidecadal variability makes climate change detection a challenge, since Global Warming evolves on a similar timescale. The ongoing discussion about a potential anthropogenic signal in the Atlantic hurricane activity is an example. A lot of work was devoted during the last years to understand the dynamics of the multidecadal variability, and external as well as internal mechanisms were proposed. This White Paper focuses on the internal mechanisms relevant to the Atlantic Multidecadal Oscillation/Variability (AMO/V) and the Pacific Decadal Oscillation/Variability (PDO/V). Specific attention is given to the role of the Meridional Overturning Circulation (MOC) in the Atlantic. The implications for decadal predictability and prediction are discussed

The impact of current and possibly future sea surface temperature anomalies on the frequency of Atlantic hurricanes

A brief summary of the current capabilities of a high resolution global numerical prediction model towards resolving the life cycles of hurricanes is first presented. Next, we illustrate the results of season long integrations for the years 1987 and 1988 using the observed sea surface temperature (SST) anomalies over the global oceans. The model being used here is the FSU atmospheric global spectral model at the horizontal resolution of T42 and with 16 vertical layers. The main emphasis of this study is on hurricane tracks for these and for global warming experiments. The global warming scenarios were modeled using doubled CO2 and enhanced SST anomalies. The model being atmospheric does not simulate the ocean, and SST anomalies need to be prescribed. It is assumed in these experiments that the SST anomalies of the doubled CO2 world appear similar to those of the current period but that they are slightly warmer over the global tropics. That is determined using a simple proportionality relationship requiring an enhancement of the global mean SST anomaly over the tropics. Such an enhancement of the SST anomaly of an El Nino year 1987 amplifies the SST anomaly for the El Nino of the double CO2 atmosphere somewhat. The La Nina SST anomalies were similarly enhanced for the double CO2 atmosphere during 1988. These hurricane season experiments cover the period June through October for the respective years. It was necessary to define the thresholds for a model simulated hurricane; given such a definition we have compared first the tracks and frequency of storms based on the present day CO2 simulations with the observed storms for 1987 and 1988. Those comparisons were noted to be very close to the observed numbers of the storms. The doubled CO2 storms show a significant enhancement of the frequency of storms for the La Nina periods, however there was no noticeable change for the El Nino experiments. We have also run an experiment using the SST anomalies from a triple CO2 climate run made at the Max Planck Institut at Hamburg, This experiment simulated some 7 hurricanes over the Atlantic Ocean. The intensity of hurricanes, inferred from maximum winds at 850 mb, show that on the average the storms are slightly more intense for the double CO2 experiments compared to the storms simulated from current CO2 conditions. The triple CO2 storms were slightly stronger in this entire series of experiments

Tropical air-sea interaction in general circulation models

An intercomparison is undertaken of the tropical behavior of 17 coupled ocean-atmosphere models in which at least one component may be termed a general circulation model (GCM). The aim is to provide a taxonomy—a description and rough classification—of behavior across the ensemble of models, focusing on interannual variability. The temporal behavior of the sea surface temperature (SST) field along the equator is presented for each model, SST being chosen as the primary variable for intercomparison due to its crucial role in mediating the coupling and because it is a sensitive indicator of climate drift. A wide variety of possible types of behavior are noted among the models. Models with substantial interannual tropical variability may be roughly classified into cases with propagating SST anomalies and cases in which the SST anomalies develop in place. A number of the models also exhibit significant drift with respect to SST climatology. However, there is not a clear relationship between climate drift and the presence or absence of interannual oscillations. In several cases, the mode of climate drift within the tropical Pacific appears to involve coupled feedback mechanisms similar to those responsible for El Niño variability. Implications for coupled-model development and for climate prediction on seasonal to interannual time scales are discussed. Overall, the results indicate considerable sensitivity of the tropical coupled ocean-atmosphere system and suggest that the simulation of the warm-pool/cold-tongue configuration in the equatorial Pacific represents a challenging test for climate model parameterizations

The 1983 drought in the West Sahel: a case study

Some drought years over sub-Saharan west Africa (1972, 1977, 1984) have been previously related to a cross-equatorial Atlantic gradient pattern with anomalously warm sea surface temperatures (SSTs) south of 10°N and anomalously cold SSTs north of 10°N. This SST dipole-like pattern was not characteristic of 1983, the third driest summer of the twentieth century in the Sahel. This study presents evidence that the dry conditions that persisted over the west Sahel in 1983 were mainly forced by high Indian Ocean SSTs that were probably remanent from the strong 1982/1983 El Niño event. The synchronous Pacific impact of the 1982/1983 El Niño event on west African rainfall was however, quite weak. Prior studies have mainly suggested that the Indian Ocean SSTs impact the decadal-scale rainfall variability over the west Sahel. This study demonstrates that the Indian Ocean also significantly affects inter-annual rainfall variability over the west Sahel and that it was the main forcing for the drought over the west Sahel in 1983

Forecasting global ENSO-related climate anomalies

Long-range global climate forecasts have been made by use of a model for predicting a tropical Pacific sea surface temperature (SST) in tandem with an atmospheric general circulation model. The SST is predicted first at long lead times into the future. These ocean forecasts are then used to force the atmospheric model and so produce climate forecasts at lead times of the SST forecasts. Prediction of the wintertime 500 mb height, surface air temperature and precipitation for seven large climatic events of the 1970 to 1990s by this two-tiered technique agree well in general with observations over many regions of the globe. The levels of agreement are high enough in some regions to have practical utility. -Author

The Genus Harmonia (Coleoptera, Coccinellidae) in the Middle East Region

Şenal, Derya (Bilecik, Author)The harlequin ladybird, Harmonia axyridis (Pallas, 1773), is native to Asia buthas been introduced to many countries, both intentionally and unintentionally. In the MiddleEast region, H. axyridis was so far only known from Iran and Turkey. This study reports H.axyridis for the fi rst time from a country with a hot desert climate, Saudi Arabia. The singlespecimen that was found is most likely the result of unintentional release. Successful spreadingof H. axyridis in Saudi Arabia will be limited because of high temperatures during summerand scarcity of prey (aphids). New records from Iran and Turkey suggest fast spreading ofH. axyridis in these parts of the Middle East. In addition, we also present new records fromIran and Turkey for H. quadripunctata (Pontoppidan, 1763), the other species in the genusthat occurs in the Middle East region. A key and illustrations are provided for both species.WOS:000465172700014Q

Forecasting global ENSO-related climate anomalies

Long-range global climate forecasts have been made by use of a model for predicting a tropical Pacific sea surface temperature (SST) in tandem with an atmospheric general circulation model. The SST is predicted first at long lead times into the future. These ocean forecasts are then used to force the atmospheric model and so produce climate forecasts at lead times of the SST forecasts. Prediction of the wintertime 500mb height, surface air temperature and precipitation for seven large climatic events of the 1970 1990s by this two-tiered technique agree well in general with observations over many regions of the globe. The levels of agreement are high enough in some regions to have practical utility