By Richard Willoughby
(The author appreciates the availability NASA’s Earth Observations satellite data sets used in this analysis.)
This is a three part series that analyses the role of atmospheric water in regulating Earth’s thermal balance.
Part 3 Examines the global ocean energy balance over an annual cycle month-by-month to identify the role of atmospheric water in regulating the energy balance.
Part 3: On the role of Atmospheric Water – Albedo trumps Long Wave Absorption and Re-emission
A study of the top of atmosphere electro-magnetic radiated power flux over the global oceans covering a twelve month period from August 2019 to July 2020 reveals that water in the atmosphere provided net radiated energy loss over the annual cycle.
The cooling or heating effect of atmospheric water is found to respond to the ocean surface temperature with slightly less than one month time lag. The gradient of the radiated power loss with respect to the atmospheric water quantity varies from month-to-month and is introduced here as the Atmospheric Water Cooling Coefficient (AWCC).
(All data sourced for this study is available from NASA’s Earth Observations web site.)
Water in Earth’s Atmosphere
Water is a small but key constituent of Earth’s atmosphere. In the tropics, the total water mass distributed throughout the entire atmospheric column can be as high as 70kg/sq.m. That corresponds to 70mm or 7cm above any given surface area. At the poles, the atmosphere contains negligible water.
The water in the atmosphere can exist in three phases – gas, liquid and solid. When water evaporates from a surface, it enters the atmosphere as a gas commonly referred to as water vapour. When water vapour cools it will form a liquid condensate or solid ice depending on the atmospheric temperature where the phase change occurs. If the temperature is higher than 0C then the water vapour condenses to liquid water. If the temperature is lower than 0C then the water vapour solidifies to solid ice. Liquid water and solid ice in the atmosphere are the fundamental constituents of clouds.
Water in its three phases in the atmosphere has a profound effect on the global energy balance. All phases absorb and emit long wave electro-magnetic radiation (OLR) emitted from the surface of the earth and the atmosphere. The solid phase dominates the reflection of short wave electro-magnetic radiation (SWR) thereby reducing the insolation reaching the surface and absorbed by the oceans.
Atmospheric Water & Radiating Power
There are three electro-magnetic radiated power fluxes observed at the top of Earth’s atmosphere:
- Incoming short wave solar radiation
- Reflected short wave radiation
- Outgoing long wave radiation
The incoming insolation varies from 1320W/sq.m to 1420W/sq.m over an annual cycle due to the eccentricity in Earth’s orbit. The peak insolation occurs in early January in the present era. The area average over the spherical surface ranges accordingly from 330W/sq.m up to 355W/sq.m.
For the Earth to have a stable temperature, the incoming SWR from the sun must be balanced at the top of the atmosphere by reflected SWR and the OLR. However the insolation arriving is varying over a year resulting in energy being stored in the oceans when the insolation is high and then released when the insolation is lower. The high thermal inertia of the oceans dampens the surface temperature variation. An additional heat storage factor results from the distribution of water over the surface of the globe with the peak insolation occurring when the southern hemisphere, with its high proportion of surface water, has the highest exposure to the sun. Due to the variation in heat stored, variation in atmospheric water and global distribution of atmospheric water, it is possible to examine how atmospheric water alters Earth’s total radiated power flux (the sum of reflected SWR and OLR) throughout the year.
For convenience of analysis the year was considered in monthly intervals. The specific twelve months examined were August 2019 to July 2020. Over the twelve months, it was observed that the radiated power flux peaked in July 2020 at 360W/sq.m. in locations where atmospheric water ranged from 2cm to 3cm as displayed in Figure 13. For July 2020, there was a strong upward trend in radiating power with atmospheric water averaging 4.2W/sq.m/cm. This gives rise to the herein named coefficient, Atmospheric Water Cooling Coefficient (AWCC).
Figure 13: Radiated power flux above ocean surface as a function of atmospheric water content – July 2020. (Data courtesy NASA Earth Observatory 1X1 degree)
December 2019 also had peak radiated power flux of 360W/sq.m but the peak occurred in locations where the atmospheric water was less than 1cm per Figure 14.
Figure 14: Radiated power flux above ocean surface as a function of atmospheric water content – December 2019.
As shown in Figure 14, for December2019 the AWCC was minus 3.3W/sq.m/cm. Of the twelve months, nine had a positive cooling coefficient and three had a negative cooling coefficient. The average AWCC over the twelve months examined was 1.39W/sq.m/cm as displayed in Figure 15.
Figure 15: Radiated power flux above ocean surface as a function of atmospheric water content – combined twelve months August 2019 to July 2020. Excludes any location having sea ice coverage during any month of the period studied.
AWCC Response to Ocean Surface Temperature
Examining the way the AWCC varied over the twelve months, it became apparent that the AWCC is responsive to the ocean surface temperature so this was tested as observed in Figure 16.
Figure 16: Atmospheric Water Cooling Coefficient charted with average Ocean Surface Temperature over twelve months – August 2019 to July 2020 for AWCC and July 2019 to June 2020 for SST advanced 1 month
In Figure 16 the temperature has been advanced one month to time adjust the lagged response. There is a delay between the ocean surface temperature increasing and the increase in the AWCC of around 20 days so advancing the temperature by one month gives better alignment of the curves. Likewise a fall in ocean surface temperature leads to a reduction in the AWCC.
AWCC and “Greenhouse Effect”
NASA provides the following description for the “Greenhouse Effect”:
The greenhouse effect is a process that occurs when gases in Earth’s atmosphere trap the Sun’s heat. This process makes Earth much warmer than it would be without an atmosphere. The greenhouse effect is one of the things that makes Earth a comfortable place to live.
The main greenhouse gases are:
- Water vapor
- Carbon dioxide
- Nitrous oxide
During the day, the Sun shines through the atmosphere. Earth’s surface warms up in the sunlight. At night, Earth’s surface cools, releasing heat back into the air. But some of the heat is trapped by the greenhouse gases in the atmosphere. That’s what keeps our Earth a warm and cozy 58 degrees Fahrenheit (14 degrees Celsius), on average.
Actual observed data shows that total ocean radiated power flux, the sum of OLR and reflected SWR, is positively correlated with water in the atmosphere over the twelve months examined. In fact the atmospheric water exhibits a regulating response to ocean surface temperature when area average is 18.5C with the AWCC positive above this value and negative below.
It is further noted that, like the twelve month total chart in Figure 15 and July chart in Figure 13, ten of the twelve individual months examined exhibited an increase in radiated power between locations having atmospheric water in the range 5 to 5.5cm and those locations above 5.5cm. That is the result of convective instability over tropical oceans.
Actual observations of the attributes of water in the atmosphere contradict the heat trapping assumption of atmospheric water described by the “Greenhouse Effect”. Water in the atmosphere is not heat trapping but rather a temperature regulating component that increases radiating power when the surface warms and reduces radiated power when the surface cools. Overall, atmospheric water is a cooling agent. Without atmospheric water, the surface of Earth’s oceans would be warmer than the current temperature, not cooler; atmospheric water is a surface temperature limiting agent with some precision at 30C (303K).
The concept of the “Greenhouse Effect” demonstrates a misunderstanding of how Earth’s average surface temperature is achieved. The energy balance of the oceans, and consequently the entire earth, are related primarily to the upper and lower thermostatic limits on ocean surface temperature. The area of 30C warm pools expand and contract in response to variation in the top of atmosphere insolation due to the orbital eccentricity combined with the extent of water surface exposed more directly to the sun. Sea ice expands and contracts in reverse to the warm pools but to reduce heat loss from water below the ice due to the low thermal conductivity of the sea ice. The temperature of the ocean water surface ranges from minus 2C (271K) to 30C (303K). It should be no surprise that the average surface temperature of the globe is 14C (574/2=287K) given the distribution of water having equatorial dominance over polar extent causing average ocean surface temperature higher than 14C and average elevation of land at 800m with more land at higher latitudes than equatorial resulting in average land temperature being slightly less than 14C.
Climate models are based on a flawed assumption. Until they can replicate the actual physics of deep convection tightly linked to surface temperature rather than the naive parameterisation of clouds they will remain nothing more than extended weather models with useful predictive ability of a few days.
I have used many months from these sets. All the charts and images are independently produced meaning not copied images from these links.
There is also data from the moored buoys that I refer to:https://www.pmel.noaa.gov/tao/drupal/disdel/