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A sidebar guide to earth.nullschool.net
Quick Reference
Air
Wind
Temp
RH
WPD
3HPA
CAPE
TPW
TCW
MSLP
MI
Wind speed + direction
Air temperature
Relative Humidity
Wind Power Density
3-hour Precip. Accumulation
Convective Potential Energy
Total Precipitable Water
Total Cloud Water
Mean Sea Level Pressure
Misery Index
Ocean
SST
SSTA
HTSGW
pCO2
FGCO2
Sea Surface Temperature
SST Anomaly
Significant Wave Height
Partial Pressure of CO2
Sea-Air CO2 Flux Density
Chem
COsc
CO2sc
SO2sm
Carbon monoxide concent.
Carbon dioxide concent.
Sulfur dioxide surface mass
Particulates
DUex
PM1
PM2.5
PM10
SO4ex
Dust extinction
Particulate Matter < 1 µm
Particulate Matter < 2.5 µm
Particulate Matter < 10 µm
Sulfate Extinction
Air
Height
Height is measured in pressure (in hectopascals, or hPa).
1 hectopascal (hPa) = 1 millibar (mb). Pressure decreases as you go higher in elevation. Because air pressure varies with temperature, heights are approximate. 
hPa
Sfc
1000
850
700
500
250
70
10
Meters
0
~100
~1,500
~3,500
~5,000
~10,500
~17,500
~26,500
Feet
0
~330
~5,000
~11,500
~16,500
~34,500
~57,500
~87,000
Layer
Sea level
Vorticity
Jet  stream
Stratosphere
Wind
Wind speed and direction at specified height. Note: animated speed relative to map is not to scale.
Temp
Air temperature at specified height
RH
Relative humidity at specified height
WPD
Instantaneous wind power density, a measure of wind power available to wind turbines
3HPA
+
+
3-hour precipitation accumulation - the total predicted amount of rain, snow, or other precipitation predicted over the next three hours
CAPE
Convective Available Potential Energy, a measure of the instability of the atmosphere. Nonzero CAPE can lead to the formation of cumulus and cumulonimbus clouds, and potentially severe weather
TPW
Total Precipitable Water, or the total amount of rain that would fall if all of the water in the air above that point were to precipitate
TCW
Total Cloud Water, or the total mass per volume of water and ice in cloud form
MSLP
Mean Sea Level Pressure, or atmospheric pressure at sea level
MI
Misery Index, or the perceived temperature (as opposed to actual temperature) due to humidity (in hot environments) or wind chill (in cold environments).
Ocean
A note on update frequency
Unlike atmospheric model data, 
- Currents are updated every 5 days
- SST and SSTA are updated daily
- Waves are updated every 3 hours
SST
SSTA
Sea Surface Temperature Anomaly,
or the difference between current SST and the average daily SST from 1981-2011
HTSGW
Significant Wave Height, the average height (from trough to crest) of the highest 1/3 of waves at a particular point in the ocean. More details on this definition here.
pCO2
Partial Pressure of CO2 in seawater at the surface. The units of pCO2 are in µatm, which is roughly equivalent to parts per million, or ppm. (Compare to ppmv of CO2sc in the Chem section). When the ocean and atmosphere interact, CO2 passes between them. When the ocean's pCO2 is lower than the atmosphere's ppmv, atmospheric CO2 is dissolved into ocean water. When the opposite is true, CO2 is released from the ocean into the atmosphere. In addition to atmospheric CO2 levels, the ocean's pCO2 levels are influenced by things like biological photosynthesis, respiration, and calcification.
FGCO2
Sea-Air CO2 Flux Density, the rate at which CO2 passes between the ocean and the atmosphere (see detail of pCO2 above). Positive values mean that more CO2 passing from the ocean to the atmosphere, negative values mean the opposite. Units are in mols per square meter per year (one mol of CO2 is approximately 44g or 1.55 oz).
Chem
COsc
The concentration of carbon monoxide in the air at the Earth's surface (note CO is measured in parts per billion per volume (ppbv) while CO2 is measured in parts per million per volume (ppmv). This is a good tool for searching for forest fires.
CO2sc
The concentration of carbon dioxide in the air at the Earth's surface
SO2sm
The mass of sulfur dioxide in the air at the Earth's surface. (Sulfur dioxide comes from both natural and man-made sources. For example, see heavily industrialized areas with many coal-fired plants. Also, find Hawaii on the map, and turn off animation to see sulfur dioxide coming from the erupting volcano Mauna Loa, as well as the exhaust from ships along major shipping lanes).
Particulates
DUex
The aerosol optical thickness (AOT) of light at 550 nm due to dust.
PM1
The mass of atmospheric particles with a diameter less than 1 micron
PM2.5
The mass of atmospheric particles with a diameter less than 2.5 microns
PM10
The mass of atmospheric particles with a diameter less than 10 microns
SO4ex
The aerosol optical thickness (AOT) of light at 550 nm due to sulfate.
About aerosol optical thickness

An aerosol is air containing particles. Common particles are dust, smoke, soot, and water droplets (clouds). These particles absorb and scatter sunlight, reducing the amount of light reaching the ground. This reduction of light as it passes through the atmosphere is called extinction.

Aerosol Optical Thickness (AOT) is (the log of) the ratio between the power of incoming light and the power of transmitted light. The thicker the aerosol, the less light passes through.

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