By Richard Willoughby
May 2021
(The author estimates the availability of the NASA Earth observation satellite datasets used in this analysis.)
Now a four-part series that analyzes the role of atmospheric water in regulating the Earth’s thermal equilibrium.
Part 1 An analysis of the temperature of warm pools in the tropical ocean and the processes of temperature limitation
Part 2 Explains the mechanism of deep convection and concludes with the persistence of clouds over the warm pools of the ocean.
part 3 Investigates the global energy balance of the oceans over an annual cycle from month to month to determine the role of atmospheric water in regulating the energy balance.
Part 4: The atmospheric gear change
Total precipitation water and free convection
In Part 2 of this analysis it was briefly mentioned that the atmosphere can only form a degree of free convection (LFC) if the total precipitation water (TPW) exceeds 30 mm. The conditions listed below all produce an LFC at 500m:
- Surface temperature 298 K, relative humidity 52% and TPW 3.1 cm
- Surface temperature 293 K, relative humidity 71% and TPW 3.1 cm
- Surface temperature 288K, saturated and TPW 3.2 cm
This shows that an LFC can form under strongly varying surface temperatures and relative humidity, but that the TPW remains constant for an LFC 500 m above the surface level close to 3.1 cm.
Part 2 also quantified the rate of condensation at 7.3 mm / day when all OLRs exist above the atmospheric column. This state will certainly continue as soon as the TPW reaches 3.1 cm, as water vapor, water condensate and ice are absorbed in long waves. With an LFC of 500 m and a TPW of 3.1 cm, there is 2.3 cm (23 mm) of water above the LFC. It would therefore take 75 hours for the column to develop the full CAPE. It is likely that divergence or other disturbances will disturb all development, so a downpour is weak.
It is observed that cloudburst cycles become more frequent once the TPW reaches 4.5 cm. Typical surface conditions for occasional downpours are 296 K and 80% humidity. This results in an LFC at 2000 m with 10 mm of water vapor above the LFC and 7 mm of water above freezing point when the relative humidity is constant. The full CAPE can be recharged in 33 hours and the cirrus cloud persistence is nominally 70% of the full CAPE development phase.
Atmosphere in overdrive
An interesting observation comes when an understanding of deep convection described in Part 2 and above is combined with the actual ToA output EMR data analyzed in Part 3. Figure 17 shows the twelve monthly regression lines for the EMR versus the TPW on a single graph.
Figure 17: Regression lines for twelve monthly plots of ToA outbound EMR flow versus TPW
Referring to Figure 17, at 4.5 cm, there is a vertical line labeled “Threshold” that gives the least squares error to the intersection points. This is the TPW where the atmosphere goes into high gear and deep convection sets in. Above the threshold, the atmospheric water cools mainly through regular downpours that catapult water vapor over the LFC to form a highly reflective cumulus cloud and then a persistent cirrus cloud while the CAPE is charging. As soon as deep convection sets in, the increased reflection of the ToA insulation trumps the decrease in the OLR, so that the ToA radiant power increases.
Below the threshold, the water vapor acts as a heating agent by lowering the radiant temperature of the atmospheric column, thereby lowering the ToA-OLR without creating a highly reflective cloud.
As the surface temperature cools, the slope of the regression lines or the atmospheric water cooling coefficient (AWCC) introduced in Part 3 is negative. It is evident that the radiant power of the atmosphere above the threshold is reduced compared to the months when the surface has warmed and the AWCC is positive.
Atmospheric water fills the atmosphere with the ability to shift gears in response to changes in surface temperature. The normal gait and overdrive conditions differ by the TPW threshold of 4.5 cm. In ordinary devices, atmospheric water is a heating medium, and in overdrive it is a coolant. It certainly does not cause a “greenhouse effect” that only warms the planet. Atmospheric water can stabilize surface temperature by allowing more surface irradiation and reducing OLR performance when the ocean surface is cool and limiting surface irradiation more than reducing OLR with reflective cloud when the surface is warm. The deep convection provides a precise regulation temperature of 30 ° C on an annual average over warm pools in the open ocean.
Current climate models parameterize clouds and atmospheric water is treated as a “greenhouse gas” if it is present in the atmosphere as a gas, liquid or solid. The solid phase is a key factor in the formation of reflective clouds. These phases all respond to the surface temperature at the bottom of the atmospheric column and the surface pressure to a much lesser extent in the observed area. The atmospheric gear change by 45 mm TPW is not a simple process that can be emulated with a few cloud parameters.
Date links for the referenced dates
https://neo.sci.gsfc.nasa.gov/view.php?datasetId=CERES_LWFLUX_M
https://neo.sci.gsfc.nasa.gov/view.php?datasetId=CERES_SWFLUX_M
https://neo.sci.gsfc.nasa.gov/view.php?datasetId=MYD28M
https://neo.sci.gsfc.nasa.gov/view.php?datasetId=MYDAL2_M_SKY_WV&date=2021-04-01
https://www.pmel.noaa.gov/tao/drupal/disdel/
Note that the data was obtained from these locations for different time intervals, usually monthly.
The author
Richard Willoughby is a retired electrical engineer with 30 years experience in the Australian mining and mineral processing industries. He has worked in large operations, corporate research and development, and mine development. He spent another ten years as a technical risk advisor in the global insurance industry, where he developed an ongoing interest in natural disasters and climate change.
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