System Earth 3a

Atmosphere III

Misha Velthuis

m.velthuis@uva.nl

Tue 17 Sept 2024

Today

Quiz (20 minutes)

Answers to quiz

Recap

Atmosphere III

Quiz

Recap: last Thursday

Geostrophic wind

Simple global model of air flow

Adding continents and oceans

Adding water vapour (first intro)

Recap: questions/ remarks

Does climate change affect
the duration of the monsoon in India?

Amount

The boxplots represent the percentage changes in summertime precipitation per one-degree Celsius (% °C−1) according to the CMIP6 models for three future scenarios relative to near-term, mid-term, and long-term periods over the Northern African (NAF), Southern African (SAF), Indian (IND), Indo-China Peninsula (ICP), East Asian (EA), western-North Pacific (WNP), Australian (AU), Northern American (NAM), and Southern American (SAM) monsoon domains. Gray symbols indicate the individual CMIP6 models whereas the boxes indicate the spread (from the 25th to the 75th percentile, with the center lines representing the median) of the CMIP6 models

Moon, S., & Ha, K. J. (2020). Future changes in monsoon duration and precipitation using CMIP6. npj Climate and Atmospheric Science, 3(1), 45.

Link to image

By the way…

Duration

Atmosphere III

Saturation vapor pressure (end)

Latent heat

Reasons for uplift

Saturation vapor pressure

Saturation vapor pressure = dynamic equilibrium

vapor pressure < saturation vapor pressure

vapor pressure > saturation vapor pressure

Saturation vapor pressure

Why does it rain when air rises?

As air rises, it cools

Air rises, it cools, it rains

Reasons for uplift

Orographic uplift

Mixing of different densities (front)

Convection

But first: latent heat

Latent heat

Phase changes

Convection at ITCZ

Hurricanes

Third reason for uplift: convection

New concepts: dry and wet adiabatic cooling

Key new term: environmental lapse rate: the rate at which the temperature goes down with altitude.

The dry/wet adiabatic rate tells us how fast the temperature of a parcel of air will go down as it rises.
The environmental lapse rate tells us how fast the temperature of the air that the rising parcel will encounter is going down with altitude.

Bottom line: if the environmental lapse rate is higher (goes down faster) than the adiabatic rate, a parcel of air will rise.

In this figure:

The environmental temperature is always lower than the temperature of the rising parcel of air.
In other words, the rate at which the parcel of air cools down as it rises, is smaller than the rate at which the air it encounters is getting colder with altitude. As a result the parcel of air will be relatively warm at every altitude, and remain positively buoyant as it rises (= it will keep rising = instable).

System Earth 3a

Atmosphere III

Misha Velthuis

m.velthuis@uva.nl

Tue 17 Sept 2024

Today

Quiz

Recap: last Thursday

Recap: questions/ remarks

Does climate change affect the duration of the monsoon in India?

Amount

By the way…

Duration

Atmosphere III

Saturation vapor pressure

Saturation vapor pressure

Saturation vapor pressure = dynamic equilibrium

vapor pressure < saturation vapor pressure

vapor pressure > saturation vapor pressure

Saturation vapor pressure

Why does it rain when air rises?

As air rises, it cools

Air rises, it cools, it rains

Reasons for uplift

Orographic uplift

Mixing of different densities (front)

Convection

Latent heat

Phase changes

Convection at ITCZ

Hurricanes

Third reason for uplift: convection

New concepts: dry and wet adiabatic cooling

Next time:

Does climate change affect
the duration of the monsoon in India?