Madden–Julian oscillation in the context of "El Niño–Southern Oscillation"

Climatology (from Greek κλίμα, klima, "slope"; and -λογία, -logia) or climate science is the scientific study of Earth's climate, typically defined as weather conditions averaged over a period of at least 30 years. Climate concerns the atmospheric condition during an extended to indefinite period of time; weather is the condition of the atmosphere during a relative brief period of time. The main topics of research are the study of climate variability, mechanisms of climate changes and modern climate change. This topic of study is regarded as part of the atmospheric sciences and a subdivision of physical geography, which is one of the Earth sciences. Climatology includes some aspects of oceanography and biogeochemistry.

The main methods employed by climatologists are the analysis of observations and modelling of the physical processes that determine climate. Short term weather forecasting can be interpreted in terms of knowledge of longer-term phenomena of climate, for instance climatic cycles such as the El Niño–Southern Oscillation (ENSO), the Madden–Julian oscillation (MJO), the North Atlantic oscillation (NAO), the Arctic oscillation (AO), the Pacific decadal oscillation (PDO), and the Interdecadal Pacific Oscillation (IPO). Climate models are used for a variety of purposes from studying the dynamics of the weather and climate system to predictions of future climate.

A Hovmöller diagram is a common way of plotting meteorological data to highlight the behavior of waves, particularly tropical waves. The axes of Hovmöller diagrams depict changes over time of scalar quantities such as temperature, density, and other values of constituents in the atmosphere or ocean, such as depth, height, or pressure. Typically in that case, time is recorded along the abscissa, or x-axis, while 'vertical' values (of depth, height, pressure, etc.) are plotted along the ordinate, or y-axis.

The alternate orientation of axes may also be used, as a Hovmöller diagram may be plotted for longitude or latitude on the abscissa and for (advancing) time on the ordinate; then the contour values of a named physical field may be presented through color or shading.

Paul Rowland Julian (born October 12, 1929), a Fellow of the American Meteorological Society, is an American meteorologist who served as a longtime staff scientist at the National Center for Atmospheric Research (NCAR), was co-author with Roland Madden of the study establishing the Madden–Julian oscillation (MJO), and contributed to the international, multi-institutional Global Atmospheric Research Program (GARP), Tropical Wind, Energy Conversion, and Reference Level Experiment (TWERLE), and Tropical Ocean-Global Atmosphere (TOGA) meteorology research programs. The MJO meteorologic phenomenon he co-discovered is the largest element of the intraseasonal variability in the tropical atmosphere, a traveling pattern arising from large-scale coupling between atmospheric circulation and tropical deep convection. Description of the MJO remains an important contribution to climate research with relevance to modern short- and long-term weather and climate modeling.