Author: Charles Blaisdell, Ph.D. Chemical Engineer
abstract
Yes, it's about hot air, hot air and low humidity air coming from any patch of land, resulting in lower annual evaporation of water over time (many years). Due to the lack of evaporative cooling, this type of plot has higher temperatures and lower specific humidity SH than its original state, and can create plumes that block higher “vapor pressure deficit” VPD air. Urban heat islands, urban heat island effect, forest to farmland, forest fires and mining are all typical examples of such plots. The size of this plume is an amplification factor for cloud delay. High VPD air mixes with air passing through lower cloud zones (cumulus heights) and delays cloud formation somewhere.
Data from weather balloon “soundings” indicate that over cloud-free UHI a stream of higher VPD air is produced whose area may be 1 to 4 times larger than that of UHI, consistent with models. The plume is created by the lower density of hot-low specific humidity SH air (lower ET, evapotranspiration) rising from the UHI and forcing turbulence (mixing) with the very low SH air in the upper atmosphere. On cloudy days, cooler higher SH air has higher density and specific humidity and does not rise as quickly or at all. The cloud-free sounding data also indicate that the cloud-delayed VPD is preserved as air rises from the massif.
Plumes amplify the size of high VPD air in a particular patch and may become a climate change factor if the size, water evaporation, or albedo of the particular patch changes. Cities are expanding, forest land is decreasing, and mining is increasing. The amount of change in all special regions of the planet is not yet known, but is likely to be enormous. Plume size will amplify any special effects of climate change on cloud cover (or albedo).
introduce
Scientists have long known that Earth's cloud cover (CC) is a key part of seasonal and annual climate variability (1). WUWT's Willis Eschenbach (2) proposed a theory about how increasing cloud cover could cool the Earth (or how decreasing cloud cover could warm the Earth). The author fully agrees with the Willis theory and proposes a theory as to what causes changes in cloud cover. The theory of Reduced Cloud Global Warming (CRGW) is that over time, water evaporation from specific lands on Earth decreases (UHI, deforestation, mining, etc.), causing higher VPD air to rise in plumes to Delays the formation of cloud cover or thinner clouds. There are fewer clouds, more sunlight, higher temperatures, and more water evaporation, which can be considered a higher global specific humidity. The CRGW theory is most applicable to the period from 1970 to the present. The subject of this article is the plume part of the theory.
Figure 1. Plume visuals provided by Ann Cosgrove and Max Berkelhammer(3)
An important variable in the CRGW model is the size of the hot dry air plume that rises due to local land changes, see Figure 1 . Plume size increases the area of Earth over which high VPD air can delay (or dilute) cloud formation. For example, if a UHI has area X and produces a plume twice the size of the UHI, the area of Earth affected by the UHI is 2X. Ann Cosgrove and Max Berkelhammer (2021) (3) modeled a plume over Chiago that was 2-4 times larger than its source UHI. Fan Yifan et al. (2017) (4) also obtained roughly the same results. This plume is warmer and drier than the surrounding air, giving the plume a higher VPD (less potential cloud cover).
VPD and cloud cover (score)
VPD (Vapor Pressure Deficit) is defined as the difference between saturated vapor pressure Psw and actual vapor pressure Pw (VPD = Psw – Pw). VPD is a logical relationship between atmospheric temperature and humidity (specific humidity, SH) that predicts the chance of cloud formation. As VPD approaches 0, the atmosphere becomes saturated and cloud formation is likely. (Although, super saturation (no clouds) may occur, or particles in the air may cause clouds before 0). On a single point basis, VPD is very nonlinear: clouds are 0 and no clouds > 0. For more information on VPD and cloud, see Blaisdell (2024) (10).
Sound and plume size
To better understand rising air over urban heat islands, weather balloon “soundings” were analyzed to get some clues about plume size. Weather balloon soundings are released around the world twice a day at 12 noon and 12 am GMT (Zulu time). For plume size, the data need to be sunny and cloudless. The chosen location is a group of urban agglomerations called “Quad Cities Ia.-Il”. (Davenport, IL, Bettendorf, IL, Moline, IL, Rock Island, IL). The region has grown to include other cities, including Coal Valley Airport, which provides land-based weather data. The balloons are released at 6:00 am and 6:00 pm local time in the middle of the Quad Cities (Davenport, Iowa), not far from the airport. The 6:00 pm time works in the summer, but not in the winter (there is no sunlight at 6:00 pm in the winter). The University of Wyoming College of Engineering (5) conducted the July 2022 soundings and ranked daily weather data from the Weather Underground (6) for cloud-free days to obtain a representative sample of days with higher plume potential.
Meteorologists plot the sounding data on a strange graph called “slope T log P” (the x-axis (temperature) is tilted 45⁰ to the right, and the y-axis (pressure) is on a logarithmic scale (this plotting method may be used All data retained) Charts with mixing ratio (specific humidity), dew point isolines added to help; but for climate change, clear sky data provide some insight into the invisible plumes produced by UHI rising air, see the website ( 7 ) for a detailed summary of the Skew T Log P plot.
Skewed T Log P plot in Figure 2 (7).
Figure 2 is the only data set that is helpful in understanding urban heat island plumes. It is about 600-800 mb (4000m – 2000m) below the area where cumulus clouds form. Radiation is reflected at surfaces as shortwave radiation or is absorbed and reflected as longwave radiation (which heats the land and air and evaporates water) or is used by plants and evaporates water. The air produced by these processes can rise, stay, or sink, depending on its density relative to the surrounding air. Hot air rises and cold air sinks. Adding water to air reduces its density at the same temperature, but the process of water evaporation causes the air to cool down, making it denser. Buoyancy calculations are needed to determine the direction of air flow. The rising air will mix with very dry (and cold) air from the upper atmosphere. The initial velocity of this air (if rising) (in the range 0 to about 3000m) should be related to the plume size. The specific humidity SH profile (Fig. 3-a) shows the dilution of low SH air from the upper atmosphere (above 4000 m). The slope and height of SH profiles in the lower atmosphere show the availability of ground moisture (Denissen (2021) (8)), with higher and more vertical slopes indicating lower soil moisture. Likewise, a shorter rise time (cooler air does not rise as quickly as hot air) indicates higher ground moisture.
Figure 3b shows VPD, Pws-Pw, and Figure 3c shows the rising air velocity data for one detection. Above the initial rise of the hot air (about 1600m in this case), the passing weather front mixes with the surface air, forming a stream of air with a higher VPD (or T-Td) that mixes with the total air in the atmosphere, There may be reduced cloud cover somewhere in the atmosphere. The contribution of each urban heat island to total global VPD growth is very small, but the sum of all urban heat islands (and other similar phenomena such as deforestation and mining) over many years can be very large.
Based on the detected temperature data, buoyancy can be calculated. Assuming that the air rises on average 3000m, the speed of the rising air can be estimated based on the buoyancy force. Data for 38 days from July to August 2022 were screened for cloud-free daylight (higher probability of plumes with more than 3 detection data points in stable regions). Table 1 shows the 12 days of survival.
The speed of rising air is calculated by the buoyancy equation (see equation (9) for derivation):
B = (Ti – Ts)/Ts * 9.8
Where:
B = Buoyancy, unit is m/sec^2 or N/kg
Ti = Circle temperature of detection data point = Tii – 9.8 * (Hi – Hii)/1000 (K)
Tii = Dry cycle rate of initial detection temperature (K)
Hii = initial height (meters)
Hi = height of the detected data point (in meters)
Ts = temperature of the detection data point (K)
Speed of air rising due to buoyancy:
V = incremental distance traveled/time to travel the distance, d/t, unit is meters/second
d = incremental detection distance between data points
t = (d * 2 / B)^(1/2) seconds
The initial average velocity for clear sky soundings (see Table 1) is not directly related to the plume size, but is a very simple estimate:
Plume size, P = D / V * Hr
Where:
V = average velocity meters/second
D = distance from ground to cloud (assuming 3000m)
Hr = time of day to maintain this speed. (assuming 8 hours)
Conclusion from Table 1: There is a large variation in buoyancy velocity (and therefore plume size). The calculation formula of plume size factor Pf is:
Pf = 3000 meters to cloud height/v(m/sec) * 3600 seconds/hour * 8 hours/day
Pf = How much area is increased by the area of the special plot.
Table 1 is by no means a strict calculation of plume dimensions, but it does provide a good comparison with models (4) (3). It also means that the plume size is variable at each location, and the average value may be different at other locations. Places with less evaporation are expected to have hotter air rising, producing higher velocities and larger plumes; similarly, places with high evaporation should have smaller or no plumes.
Table 1. Clear sky data for the month of July 2022.
The actual plume may be smaller than this value due to turbulent mixing in the 2000m – 4000m range, where the SH sounds like a rapid decrease. Clear sky detection data indeed shows that high-killing cloud VPD (>0) remains within the range of 2000m to 4000m.
Plume size is an important multiplication factor in the CRGW model. A literature search revealed that not enough research has been done on the urban heat island effect or other land change plume sizes, leaving opportunities for other researchers. No physical measurements of plume dimensions could be found.
discuss
Balloon soundings show clear sky plumes consistent with models, with high VPD air generated by low ET surface air killing clouds reaching the cloud level. In the CRGW model, plume size will still be a large range (1-4x) variable. More research is needed on the global variability and size of plumes. Can satellites help? Satellites can see large amounts of smoke from forest fires. This brief study of sounding data gave me a great respect for meteorology and is the most I have ever learned about meteorology!
bibliography
- “Clouds and relative humidity in climate models; or what really regulates cloud cover?” by Walcek, C. (1996) Network linking clouds and relative humidity in climate models; or what really regulates cloud cover? ? (Technical Report) | Osti Government
Relevant
