# Assignment: Global average budgets in the CESM pre-industrial control simulation#

This notebook is part of The Climate Laboratory by Brian E. J. Rose, University at Albany.

## Learning goals#

Students completing this assignment will gain the following skills and concepts:

• Continued practice working with the Jupyter notebook

• Familiarity with atmospheric output from the CESM simulation

• More complete comparison of the global energy budget in the CESM control simulation to the observations

• Validation of the annual cycle of surface temperature against observations

• Opportunity to formulate a hypothesis about these global temperature variations

• Python programming skills: basic xarray usage: opening gridded dataset and taking averages

## Instructions#

• Complete the required problems below.

• Remember to set your cell types to Markdown for text, and Code for Python code!

• Remember to actually answer the questions. Written answers are required (not just code and figures!)

• Make sure that your notebook runs cleanly without errors:

• From the Kernel menu, select Restart & Run All

• Did the notebook run from start to finish without error and produce the expected output?

• If yes, save again and submit your notebook file

• If no, fix the errors and try again.

## Problem 1: The global energy budget in the CESM control simulation#

Compute the global, time average of each of the following quantities, and compare them to the observed values from the Trenberth and Fasullo (2012) figure in the course notes:

• Incoming Solar Radiation, or Insolation

• Reflected Solar Radiation at the top of atmosphere

• Solar Radiation Reflected by Surface

• Solar Radiation Absorbed by Surface

• Solar Radiation Refelected by Clouds and Atmosphere (you can calculate this as the difference between the reflected radiation at the top of atmosphere and reflected radiation at the surface)

• Total Absorbed Solar Radiation (ASR) at the top of atmosphere

• Solar Radiation Absorbed by Atmosphere (you can calculate this as the residual of your budget, i.e. what’s left over after accounting for all other absorption and reflection)

• Upward emission from the surface

• Downwelling radiation at the surface

• Other surface fluxes:

• “Thermals”, or sensible heat flux. You will find this in the field called SHFLX in your dataset.

• “Evapotranspiration”, or latent heat flux. You will find this in the field called LHFLX in your dataset.

Note we will look more carefully at atmospheric absorption and emission processes later. You do not need to try to calculate terms such as “Emitted by Atmosphere” or “Atmospheric Window”

• Is the CESM control simulation at (or near) energy balance?

• Do you think this simulation is near equilibrium?

• Summarize in your own words what you think are the most important similarities and differences of the global energy budgets in the CESM simulation and the observations.

## Problem 2: Verifying the annual cycle in global mean surface temperature against observations#

In the class notes we plotted the timeseries of global mean surface temperature in the CESM control simulation, and found an annual cycle. The purpose of this exercise is to verify that this phenomenon is also found in the observed temperature record. If so, then we can conclude that it is a real feature of Earth’s climate and not an artifact of the numerical model.

For observations, we will use the NCEP Reanalysis data.

Reanalysis data is really a blend of observations and output from numerical weather prediction models. It represents our “best guess” at conditions over the whole globe, including regions where observations are very sparse.

The necessary data are all served up over the internet. We will look at monthly climatologies averaged over the 30 year period 1981 - 2010.

You can browse the available data here: https://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.derived.html

Surface air temperature is contained in a file called air.2m.mon.ltm.nc, which is found in the collection called Surface Fluxes.

Here’s a link directly to the catalog page for this data file: https://www.esrl.noaa.gov/psd/thredds/catalog/Datasets/ncep.reanalysis.derived/surface_gauss/catalog.html?dataset=Datasets/ncep.reanalysis.derived/surface_gauss/air.2m.day.ltm.nc

Now click on the OPeNDAP link. A page opens up with lots of information about the contents of the file. The Data URL is what we need to read the data into our Python session. For example, this code opens the file and displays a list of the variables it contains:

import xarray as xr
url = "http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/ncep.reanalysis.derived/surface_gauss/air.2m.mon.ltm.nc"
ncep_air2m = xr.open_dataset(url, decode_times=False)

ncep_air2m

<xarray.Dataset>
Dimensions:             (lat: 94, lon: 192, time: 12, nbnds: 2)
Coordinates:
* lat                 (lat) float32 88.54 86.65 84.75 ... -84.75 -86.65 -88.54
* lon                 (lon) float32 0.0 1.875 3.75 5.625 ... 354.4 356.2 358.1
* time                (time) float64 -1.577e+07 -1.577e+07 ... -1.576e+07
Dimensions without coordinates: nbnds
Data variables:
climatology_bounds  (time, nbnds) float64 ...
air                 (time, lat, lon) float32 ...
valid_yr_count      (time, lat, lon) float32 ...
Attributes:
Conventions:                    COARDS
description:                    Data is from NMC initialized reanalysis\n...
platform:                       Model
NCO:                            20121012
history:                        Created 2021/07/26 by doMonthLTMNC4
title:                          monthly mean air.2m from the NCEP Reanalysis
dataset_title:                  NCEP-NCAR Reanalysis 1
References:                     http://www.psl.noaa.gov/data/gridded/data...
not_missing_threshold_percent:  minimum 3% values input to have non-missi...
_NCProperties:                  version=2,netcdf=4.7.0,hdf5=1.10.5,

The temperature data is called air. Take a look at the details:

ncep_air2m.air

<xarray.DataArray 'air' (time: 12, lat: 94, lon: 192)>
[216576 values with dtype=float32]
Coordinates:
* lat      (lat) float32 88.54 86.65 84.75 82.85 ... -84.75 -86.65 -88.54
* lon      (lon) float32 0.0 1.875 3.75 5.625 7.5 ... 352.5 354.4 356.2 358.1
* time     (time) object 0001-01-01 00:00:00 ... 0001-12-01 00:00:00
Attributes: (12/13)
long_name:     Long Term Mean Monthly Mean of Air Temperature
valid_range:   [150. 400.]
units:         degK
precision:     2
GRIB_id:       11
GRIB_name:     TMP
...            ...
level_desc:    2 m
statistic:     Long Term Mean
parent_stat:   Mean
dataset:       NCEP Reanalysis Derived Products
actual_range:  [199.70786 312.07498]
_ChunkSizes:   [  1  94 192]

Notice that the dimensions are (time: 12, lat: 94, lon: 192). The time dimension is calendar months. But note that the lat/lon grid is not the same as our model output!

Think about how you will handle calculating the global average of these data.

• Make a well-labeled timeseries graph of the global-averaged observed average surface air temperature climatology.

• Verify that the annual cycle we found in the CESM simulation also exists in the observations.

• In your own words, suggest a plausible physical explanation for why this annual cycle exists.

## Credits#

This notebook is part of The Climate Laboratory, an open-source textbook developed and maintained by Brian E. J. Rose, University at Albany.