Hovmöller diagram
The Hovmöller diagram is a common representation of data in meteorology and ozeonography , with which both the temporal change and the spatial variability of a quantity can be represented in a diagram.
Layout and function
In the Hovmöller diagram, a scalar quantity is generally plotted against a space-time scale. A spatial dimension is typically plotted along one axis and time is plotted on the other. The spatial component can be, for example, the geographical latitude , the geographical longitude , but also the height ( vertical profile ). A third, scalar measured value (such as temperature, pressure) or a characteristic value can then be color-coded. There are also diagrams under the name in which such latter quantities are plotted along the axis if they correlate to a spatial dimension (such as air pressure ↔ altitude).
The representation goes back to Ernest Aabo Hovmøller (1912–2008), a Danish meteorologist who presented this shape in 1949.
The diagram is particularly suitable for visualizing dynamic processes in synopsis , climatology or atmospheric physics and oceanography , such as propagation and wave phenomena , or the periods of the macroscale mechanisms of the ocean and atmosphere climate system (oscillations of teleconnection ).
Examples
| The diagram on the left shows the position of the highs in red tones and lows in blue tones; diagonal structures of the upper half show the regular westerly wind drift of about 8 degrees of longitude per day. Vertical patterns are created by a blockade in which the action centers remain stationary. This blockage is quantified in the diagram on the right.
The hemisphere-wide blockade is caused by strong standing Rossby waves of the northern jet stream , and is related to an intensified El Niño (particularly high pressures and strong blockages in the Pacific around 180 °). It causes extreme weather conditions worldwide. The period is spring / early summer 2015, with heat waves in India in May, in Pakistan and Central Asia in June, in Europe and the American west coast in July. The first chart is the classic trough -and- bridges -diagram (Trough-and-Ridge Diagram) , as it was presented by Hovmöller. |
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| X-axis: longitude (0 ° –0 ° eastward) Y-axis: time (in 5-day intervals) Color scale: mean 500-hPa altitude anomaly over 45 ° N-60 ° N, 5-day moving average |
X-axis: length (90 ° E – 90 ° E eastward) Y-axis: time (in 5-day intervals) color scale: blocking index (Tibaldi-Molteni) |
| The diagram shows the deviations in the wind direction of the high-altitude currents in the period 1981–1991 (westerly winds red, easterly winds blue, zero line black) in the vicinity of the equator depending on the air pressure. The spatial component is not measured in a length scale, but indicated using the air pressure. Thus, the height range (the y-axis) corresponds approximately to a height of 20 to 35 km above the earth's surface.
The diagram illustrates fluctuations in the jet stream that are likely to be related to solar activity. |
literature
- Ernest Hovmöller: The Trough-and-Ridge diagram . In: Tellus . tape 1 , no. 2 , May 1949, p. 62-66 , doi : 10.1111 / j.2153-3490.1949.tb01260.x .
Web links
Individual evidence
- ↑ Construction of Hovmöller Diagrams. Chapter 3. in DA Ahijevych, RE Carbone, JD Tuttle, SB Trier: Radar Data and Climatological Statistics Associated with Warm Season Precipitation Episodes over the Continental US NCAR Technical Note 448 + STR, doi: 10.5065 / D6PK0D39 ( download pdf , on opensky. ucar.edu; online , web.archive.org).
- ↑ a b Connaissez-vous les diagrams de Hovmoller? In: La chronique météo de Philippe Jeanneret . April 26, 2011, accessed July 14, 2015.
- ↑ cf. Anomalous Equatorial Zonal Wind. Figure T14 of the Climate Diagnostics Bulletin , NOAA-NWS-CPC.