System Earth 2b

Atmosphere II

Misha Velthuis

m.velthuis@uva.nl

Fri 13 Sept 2024

Last Tuesday

Driving force

Vertical

Horizontal

Meridional

Zonal

Extra stuff #1

Extra stuff #2

Possible quiz questions

Today

Geostrophic wind

Simple global model of air flow

Adding continents and oceans

Adding water vapour

Geostrophic wind

Geostrophic wind without friction

Geostrophic wind with friction

Simple global surface flow model

Surface flows

Does it fit with our lives?

The world right now

Adding land and water

Thermal conductivity

The rate at which heat passes through a column of material,

given a certain temperature gradient.

Water = high thermal conductivity

Good at passing on heat.

Land = low thermal conductivity

Bad at passing on heat.

Heat capacity

The energy required to raise the temperature of a unit of mass

of a substance by 1 K without changing its volume.

Water = high heat capacity

Lot of energy required to raise temperature

Land = low heat capacity

Little energy required to raise temperature

Other relevant differences

Water = the water (and thus the heat it absorbs) is mixed

Water = some radiation passes through top layer and is absorbed by lower layers

As a result

On water, heat mixes/spreads +

increases and decreases slowly.

On land, heat does not mix/spread +

increases and decreases quickly.

Resulting dynamics

Sea breeze

Quick check

Link to hourly data KNMI

import pandas as pd
import matplotlib.pyplot as plt

# Read data
df = pd.read_csv('/home/misha/Downloads/ijmuide/jaren.txt', skiprows=31, header=0)

# Remove spaces in column names
df = df.rename(columns=lambda x: x.replace(' ', ''))

# Turn data to numerical data
df = df.apply(pd.to_numeric, errors='coerce')

# Get average wind speed per hour of the day
df = df.groupby('HH')['FF'].mean().reset_index()

# Visualize
plt.bar(df['HH'], df['FF'])
plt.xlabel('Hour of the Day')
plt.ylabel('Average Wind Speed (in 0.1 m/s)')
plt.title('Average Wind Speed per Hour (IJmuiden 2011-2020)')
plt.grid(True)

plt.savefig('/home/misha/Nextcloud/mnotes/org-roam/presentations/images/wind-speed2.png')

Actually, it would be interesting to also explore wind direction. Anyone?

Continentality: temperature

Because remember:

Continentality: pressure

In January…
… continents cool down fast: relatively high pressure zones
… oceans cool down slow (retain heat): relatively low pressure zones

Note that this is mean sea level pressure (MSLP): adjusted for altitude. Air pressure in Medellín is lower than in Baranquilla because it has altitude of 1600 m. (15% less oxygen). But that is corrected for in pressure maps like these.

Note that on the SH, the simple global flow model (of Kump et al. figure 4.11) remains more or less in tact: south of the ITCZ, we find a band of high pressure zones followed by a band of lower pressure zones, which is in turn followed by a band of slightly higher pressures. To be sure, these zonal bands are "disrupted" by the land mass of South America, Africa and Australia, but they remain clearly visible. Also, the location of these bands doesn't change that much across the year.

On the NH, in contrast, the bands are more severly disrupted by the (more prominent) presence of land mass.

Note that these are averages. Zoom.earth shows that reality can deviate from these averages.

Continentality: pressure

Monsoon

Happening right now.

Adding water vapour

Water vapor

Water in gas phase

Clouds

Water drops (liquid phase) or ice crystals (solid phase) suspended in the atmosphere

Phase changes

Phase exchange at the interface

Evaporation:

The higher the temperature (average kinetic energy of molecules), the more water molecules attain the "escape velocity" to escape the bonds of liquid water, the more evaporation.

Condensation:

The higher the water vapor concentration, the more likely water molecules are "caught" again by the molecular bonds of liquid water.

Dynamic equilibrium

When evaporation = condensation. At this point we say that the vapor pressure has reached the "saturation vapor pressure".

At different temperatures, the water vapor concentration at which there exists a dynamic equilibrium (the saturation vapor pressure) is different.

Kump et al. on vapor pressure:

"One way of expressing the amount of water vapor present in the atmosphere is to measure the contribution that water vapor makes to the atmospheric pressure. We saw in Chapter 3 that air is composed of numerous different gasses. Each gas exerts its own pressure. What is measured as the atmospheric pressure is the sum of all partial pressures of the individual gases - that is, the pressure each gas would exert if it were the only gas present. The pressure exerted by water vapor is referred to as the vapor pressure." (p. 78)

vapor pressure < saturation vapor pressure

vapor pressure > saturation vapor pressure

Saturation vapor pressure

Air rises, it cools, it rains

Latent heat

Hurricanes

Tuesday: quiz 1

Read all literature

Study slides