R Code for Climate Mathematics:
Theory and Applications
A Cambridge University Press book By
SSP Shen and RCJ Somerville
Version 1.0 released in July 2019 and coded by Dr. Samuel Shen, Distinguished Professor
San Diego State University, California, USA
Email: sshen@sdsu.edu
Version 2.0 compiled and updated by Momtaza Sayd
San Diego State University May 2021
Version 3.0 compiled and updated by Joaquin Stawsky
San Diego State University June 2022
Chapter 3: Basic Statistical Methods for Climate Data Analysis
Mean, variance, standard deviation, skewness, kurtosis, and quantiles
#R can directly read data from a remote data website
setwd("~/sshen/climmath/data") #set the working directory
dat1 <- read.table("aravg.ann.land_ocean.90S.90N.v4.0.0.2015.txt")
dim(dat1)## [1] 136 6tmean15 <- dat1[,2] #Take only the second column of this data matrix
head(tmean15) #The first five values## [1] -0.367918 -0.317154 -0.317069 -0.393357 -0.457649 -0.468707#[1] -0.367918 -0.317154 -0.317069 -0.393357 -0.457649 -0.468707
mean(tmean15)## [1] -0.2034367#[1] -0.2034367
sd(tmean15)## [1] 0.3038567#[1] 0.3038567
var(tmean15)## [1] 0.09232888#[1] 0.09232888
library(e1071) ## Warning: package 'e1071' was built under R version 4.1.3#This R library is needed to compute the following parameters
#install.packages("e1071") #if it is not installed on your computer
skewness(tmean15)## [1] 0.7141481#[1] 0.7141481
kurtosis(tmean15)## [1] -0.3712142#[1] -0.3712142
median(tmean15)## [1] -0.29694#[1] -0.29694
quantile(tmean15,probs = c(0.05,0.25, 0.75, 0.95))## 5% 25% 75% 95%
## -0.5792472 -0.4228540 -0.0159035 0.3743795# 5% 25% 75% 95%
#-0.5792472 -0.4228540 -0.0159035 0.3743795
Correlation, covariance, and linear trend
#Plot Fig. 3.1
yrtime15 <- seq(1880, 2015)
reg8015 <- lm(tmean15 ~ yrtime15)
# Display regression results
reg8015##
## Call:
## lm(formula = tmean15 ~ yrtime15)
##
## Coefficients:
## (Intercept) yrtime15
## -13.208662 0.006678par(mar = c(4,4,4,1))
# Plot the temperature time series and its trend line
plot(yrtime15,tmean15,xlab = "Year",ylab = "Temperature [°C]",
main = "Global Annual Mean Land and Ocean Surface\nTemperature Anomalies 1880-2015", type = "l", lwd = 2,
cex.lab = 1.1,cex.axis = 1.1,cex.main = 1.35)
abline(reg8015, col = "red")
text(1932, 0.4, "Linear Temperature Trend 0.67 °C/century",
col = "red",cex = 1.1)
#Covariance
x <- yrtime15
y <- tmean15
cov(x, y)## [1] 10.36856#Correlation
cor(tmean15, yrtime15)## [1] 0.8659857#Verify this result by formulas
x <- yrtime15
y <- tmean15
sx <- sd(yrtime15)
sy <- sd(tmean15)
cxy <- cov(x,y)
rxy <- cxy/(sx*sy)
#The same result as cor(tmean15, yrtime15)
rxy## [1] 0.8659857#Verify the linear trend by formulas
rxy*sy/sx #verified## [1] 0.006677908cxy/sx^2 #verified## [1] 0.006677908
Histogram of a set of data
h <- hist(tmean15, main = "Histogram of 1880-2015 Temperature Anomalies",
xlab = expression(paste("Temperature Anomalies [", degree, "C]")),
xlim = c(-1,1), ylim = c(0,50))
xfit <- seq(-1,1, length = 100)
areat <- sum((h$counts)*diff(h$breaks[1:2]))#Normalization area
#diff(h$breaks[1:2]) <- h$breaks[2] - h$breaks[1]
#is the histogram's bin width
yfit <- areat*dnorm(xfit, mean = mean(tmean15), sd = sd(tmean15))
#Plot the normal fit on the histogram
lines(xfit,yfit,col = "blue",lwd = 2,cex.lab = 1.1,cex.axis = 1.1,cex.main = 1.35)
Box plot
boxplot(tmean15, ylim = c(-0.8,0.8),
ylab = expression(paste("Temperature Anomalies [", degree, "C]")),
cex.lab = 1.1)
Plot Fig. 3.4
#Use setwd("working directory") to work in the desired directory
#rm(list = ls())
setwd("~/sshen/climmath/data")
par(mgp = c(1.5,0.5,0))
ust <- read.csv("USJantemp1951-2016-nohead.csv",header = FALSE)
soi <- read.csv("soi-data-nohead.csv", header = FALSE)
soid <- soi[,2] #Take the second column SOI data
soim <- matrix(soid,ncol = 12,byrow = TRUE)
#Make the SOI into a matrix with each month as a column
soij <- soim[,1] #Take the first column for Jan SOI
ustj <- ust[,3] #Take the third column: Jan US temp data
setEPS()
# postscript("fig0304.eps", height = 7, width = 7)
par(mar = c(4.5,5,2.5,1), xaxs = "i", yaxs = "i")
plot(soij,ustj,xlim = c(-4,4), ylim = c(-8,8),
main = "January SOI and the U.S. Temperature Anomalies",
xlab = "SOI [Dimensionless]",
ylab = expression(paste("Temperature Anomalies [", degree, "F]")),
pch = 19, cex.lab = 1.1,cex.axis = 1.1,cex.main = 1.35)
#Plot the scatter plot
soiust <- lm(ustj ~ soij) #Linear regression
abline(soiust, col = "blue", lwd = 4) #Linear regression line
# dev.off()
Plot Fig. 3.5
#Q-Q plot for the standardized temperature anomalies
tstand <- (tmean15-mean(tmean15))/sd(tmean15)
set.seed(101)
qn <- rnorm(136) #Simulate 136 points by N(0,1)
qns <- sort(qn)#Sort the points
qq2 <- qqnorm(qns,col = "blue",lwd = 2,cex.lab = 1.1,cex.axis = 1.1,cex.main = 1.35)
setEPS()
# postscript("fig0305.eps", height = 7, width = 7)
par(mar = c(4.5,5,3,1), xaxs = "i", yaxs = "i")
qt <- qqnorm(tstand,
main = "Q-Q plot for the Standardized Global Temp.\n Anomalies vs N(0,1)",
ylab = "Quantile of Temperature Anomalies",
xlab = "Quantile of N(0,1)", xlim = c(-3,3),ylim = c(-3,3),
cex.lab = 1.1,cex.axis = 1.1,cex.main = 1.35)
qqline(tstand, col = "red", lwd = 3)
points(qq2$x, qq2$y, pch = 19, col = "purple")
# dev.off()
Plot Fig. 3.6
plot.new()
layout(matrix(c(1,2,3), 1, 3, byrow = TRUE),
widths = c(3,3,3), heights = c(1,1,1))
lasvegas <- c(0.58,0.42)
sandiego <- c(0.4,0.6)
seattle <- c(0.16,0.84)
names(lasvegas) <- c("Clear","Cloudy")
names(sandiego) <- c("Clear","Cloudy")
names(seattle) <- c("Clear","Cloudy")
barplot(lasvegas,col = c("skyblue","gray"), ylim = c(0,1),
ylab = "Probability", cex.lab = 1.2)
mtext("Las Vegas", side = 3, line = 1)
barplot(sandiego,col = c("skyblue","gray"), ylim = c(0,1))
mtext("San Diego", side = 3, line = 1)
barplot(seattle,col = c("skyblue","gray"), ylim = c(0,1))
mtext("Seattle", side = 3, line = 1)
mtext(expression(bold("Probability Distribution of Cloudiness")),
cex = 1.2,side = 3, line = -1.5, outer = TRUE)
Plot Fig. 3.7
# Density function, probability, and normalization of N(0,1)
#par(mar = c(4.0,4.0,1.5,0.5))
cord.x <- c(-3,seq(-3,3,0.01),-1)
cord.y <- c(0,dnorm(seq(-3,3,0.01)),0)
# Make a curve
curve(dnorm(x,0,1), xlim = c(-3,3), lwd = 3,
main = 'PDF of the Standard Normal Distribution',
xlab = "Random Variable x",
ylab = 'Probability Density',
cex.lab = 1.1,cex.axis = 1.1,cex.main = 1.35)
# Add the shaded area using many lines
polygon(cord.x,cord.y,col = 'skyblue')
polygon(c(-1.5,-1.5, -1.2, -1.2),c(0, dnorm(-1.5),
dnorm(-1.2), 0.0),col = 'white')
text(0,0.18, "Area = 1", cex = 1.1)
text(-1.65,0.045,"f(x)")
text(-1.35,0.075,"dx")
text(-1.6,0.0125,"x")
text(-0.9,0.0125,"x + dx")
arrows(-2,0.2,-1.35,0.13, length = 0.1)
text(-2,0.21,"dA = f(x)dx")
text(0,0.09,expression(paste(integral(f(x)*dx,- infinity,infinity)," = 1")))
Plot Fig. 3.8
#Normal distribution plot
x <- seq(-8, 8, length = 200)
plot(x,dnorm(x, mean = 0, sd = 1), type = "l", lwd = 4, col = "red",
ylim = c(0,1),
xlab = "Random Variable x",
ylab = "Probability Density",
main = expression(Normal~Distribution ~ N(mu,sigma^2)))
lines(x,dnorm(x, mean = 0, sd = 2), type = "l", lwd = 2, col = "blue")
lines(x,dnorm(x, mean = 0, sd = 0.5), type = "l", lwd = 2, col = "black")
lines(x,dnorm(x, mean = 3, sd = 1), type = "l", lwd = 2, col = "purple")
lines(x,dnorm(x, mean = -4, sd = 1), type = "l", lwd = 2, col = "green")
# ex.cs1 <- expression(plain(sin) * phi, paste("cos", phi))
ex.cs1 <- expression(paste(mu, " = 0",~","~ sigma," = 1"),
paste(mu, " = 0",~","~ sigma, " = 2"),
paste(mu, " = 0",~","~ sigma, " = 1/2"),
paste(mu, " = 3",~","~ sigma, " = 1"),
paste(mu, " = -4",~","~ sigma, " = 1"))
legend("topleft",legend = ex.cs1, lty = 1,
col = c('red','blue','black','purple','green'), cex = 1, bty = 'n')
Calculate probability from a normal distribution
mu <- 0
sig <- 1
intg <- function(x){(1/(sig*sqrt(2*pi)))*exp(-(x-mu)^2/(2*sig^2))}
integrate(intg,-2,2)## 0.9544997 with absolute error < 1.8e-11#Or using the R built-in function dnorm to get the same result
integrate(dnorm,-2,2)## 0.9544997 with absolute error < 1.8e-11integrate(dnorm,-1.96,1.96)## 0.9500042 with absolute error < 1e-11
Plot Fig. 3.9
#Plot t-distribution by R
n <- 50
x <- seq(-4, 4, length = 200)
plot(x,dt(x, df = 3), type = "l", lwd = 4, col = "red",
ylim = c(0,0.6),
xlab = "Random Variable t",
ylab = "Probability Density",
main = "Student t-distribution T(t,df)",
cex.lab = 1.1,cex.axis = 1.1,cex.main = 1.35)
lines(x,dt(x, df = 1), type = "l", lwd = 2, col = "blue")
lines(x,dt(x, df = 2), type = "l", lwd = 2, col = "black")
lines(x,dt(x, df = 6), type = "l", lwd = 2, col = "purple")
lines(x,dt(x, df = Inf), type = "l", lwd = 2, col = "green")
#ex.cs1 <- expression(plain(sin) * phi, paste("cos", phi))
ex.cs1 <- c("df = 3", "df = 1","df = 2","df = 6", expression(paste("df = ",infinity)))
legend("topleft",legend = ex.cs1, lty = 1,
col = c('red','blue','black','purple','green'), cex = 1, bty = "n")
Confidence interval simulation
mu <- 14 #true mean
sig <- 0.3 #true sd
n <- 50 #sample size
d <- 1.96*sig/sqrt(n)
lowerlim <- mu-d
upperlim <- mu+d
ksim <- 10000 #number of simulations
k <- 0 #k is the simulation counter
xbar <- 1:ksim
for (i in 1:ksim)
{
xbar[i] <- mean(rnorm(n, mean = mu, sd = sig))
if (xbar[i] >= lowerlim & xbar[i] <= upperlim)
k <- k+1
}
print(c(k,ksim),cex.lab = 1.1,cex.axis = 1.1,cex.main = 1.35)## [1] 9484 10000
Plot the histogram Fig. 3.10
hist(xbar,breaks = 51,
main = "Histogram of the Simulated\nSample Mean Temperatures",xaxt = "n",
xlab = expression(paste("Temperature [", degree, "C]")),
ylim = c(0,600),
cex.lab = 1.1,cex.axis = 1.1,cex.main = 1.35)
axis(1,pos = -20, at = c(13.92, mu, 14.08))
text(14,530,"95% Confidence Interval (13.92, 14.08)")
Plot Fig. 3.11
#Plot confidence intervals and tail probabilities
par(mar = c(2.5,3.5,2.0,0.5))
rm(list = ls())
par(mgp = c(1.4,0.5,0))
curve(dnorm(x,0,1), xlim = c(-3,3), lwd = 3,
main = 'Confidence Intervals and Confidence Levels',
xlab = "True Mean as a Random Variable", ylab = "",
xaxt = "n", cex.lab = 1.2)
title(ylab = 'Probability Density', line = 2, cex.lab = 1.2)
polygon(c(-1.96, seq(-1.96,1.96,len = 100), 1.96),
c(0,dnorm(seq(-1.96,1.96,len = 100)),0),col = 'skyblue')
polygon(c(-1.0,seq(-1.0, 1, length = 100), 1),
c(0, dnorm(seq(-1.0, 1, length = 100)), 0.0),col = 'white')
polygon(c(-3.0,seq(-3.0, -1.96, length = 100), -1.96),
c(0, dnorm(seq(-3.0, -1.96, length = 100)), 0.0),col = 'red')
polygon(c(1.96,seq(1.96, 3.0, length = 100), 3.0),
c(0, dnorm(seq(1.96, 3.0, length = 100)), 0.0),col = 'red')
points(c(-1,1), c(0,0), pch = 19, col = "blue")
points(0,0, pch = 19)
points(c(-1.96,1.96),c(0,0),pch = 19, col = "red")
text(0,0.02, expression(bar(x)), cex = 1.0)
text(-1.50,0.02, "SE", cex = 1.0)
text(-0.60,0.02, "SE", cex = 1.0)
text(1.50,0.02, "SE", cex = 1.0)
text(0.60,0.02, "SE", cex = 1.0)
text(0,0.2, "Probability\n= 0.68")
arrows(-2.8,0.06,-2.35,0.01, length = 0.1)
text(-2.5,0.09, "Probability\n= 0.025")