Atmospheric Modeling (5 ECTS)

● Lectures:– Mon 10.15-12.00, Physicum D105

– Tue 10.15-12.00, Physicum D104

● Exercises:– Mon 14.15-16.00, Physicum D105

● Teachers– Michael Boy, Dynamicum 1D01b

– Sampo Smolander, Dynamicum 1D09a

– Kenty Ortega, Dynamicum 1D16b

– Risto Makkonen, Physicum B415

● Course web page– http://www.courses.physics.helsinki.fi/fys/atmodel/

– slides, links to Fortran-guides, timetable

Atmospheric Modeling (5 ECTS)

● Preceding studies:

A basic knowledge in one programming language (Fortran, MATLAB, C+, …) is required. However, we will use the first two lectures and exercises to give a short and comprehensive introduction and training to Fortran. Each student should have access to one computer and we will help to install a Fortran compiler if not already available.

Course content

● Introduction to Fortran

● Introduction to boundary layer meteorology modeling

● Including chemistry in the model

● Implementing emissions

● Modeling aerosol dynamical processes

● Overview of atmospheric models and complex modeling techniques

Course structure

● Lectures● Exercise

– Developing a chemical transport model including biogenic emissions, chemistry and aerosol dynamics

– Bring your exercise material to the exercise session on memory stick, paper, or your laptop

● Exam– Based on lecture content

– Your model must be ready before the exam

Timetable for first week● Mon 10.15-12.00

– introduction to course

– starting Fortran introduction

– 1st exercise given (small Fortran task)

● Mon 14.15-16.00– Checking that everyone has an environment for

editing, compiling and running Fortran

● Tue 10.15-12.00– Fortran introduction continues

– Checking 1st exercise

– Example of solving an equation in Fortran

Atmospheric modeling

Atmospheric modeling

Atmospheric modeling

Emissions-anthropogenic (SO

2, black carbon, ...)

-natural (organic compounds, dust, ...)

Meteorology-transport, radiative fluxes, ...

Chemistry & aerosols-OH, O

3, photolysis, ...

-aerosol formation, condensation, ...

Atmospheric modeling

Emissions

nucleation condensationchem

istry

chemistry

Atmospheric particle formation

How to make the computer solve our equations?

Modern programming languages

C, C++

Python

Java

Perl

Actionscript

Matlab

OCaml

Why would we use a programming language from the 50's?

Fortran(FORmula TRANslation)

● Simple to learn, less mistakes by beginners● Almost all current scientific computational code

is written in Fortran– Availability of well tested libraries, especially for

mathematics

● More space for compiler optimization, fast code● Portability of code

#include <iostream> int main(){ std::cout << "Hello World!" << std::endl; return 0;}

C++

program hello print *,"Hello World!" end program hello

Fortranpublic class HelloWorld { public static void main(String[] args) {

System.out.println("Hello, world!");

}}

Java

print "Hello, World!"

Python

The classic ”Hello World!” example.

PROGRAM squarerootexample! Comments start with an exclamation point. ! Some exponentiation and squareroot computations.! You will find data type declarations, couple arithmetic operations! and an interface that will ask values for these computations. IMPLICIT NONE !do not use implicit variable declarationsREAL :: x, y

! Command line interface. Ask a number and read it in WRITE (*,*) 'Give a value (number) for x:'READ (*,*) x

y=x**2+1 ! exponentiation and addition arithmetic

WRITE (*,*) 'given value for x:', xWRITE (*,*) 'computed value of x**2 + 1:', y! SQRT(y), Return the square root of the argument yWRITE (*,*) 'computed value of SQRT(x**2 + 1):', SQRT(y)

END PROGRAM squarerootexample

Data types

INTEGER An integer number

REAL A real number

COMPLEX A pair of real numbers used in complex arithmetic

LOGICAL TRUE or FALSE

CHARACTER A string consisting one or more characters

!Variables can be initialized at their declarationIMPLICIT NONE! After declaration and initialization the value of a variable can be ! changed whenever neededINTEGER :: n0INTEGER :: n1=0

REAL :: a, bREAL :: r1=0.0

COMPLEX :: cCOMPLEX :: imag_unit=(0.1, 1.0)

CHARACTER(LEN=80) :: placeCHARACTER(LEN=80) :: name='James Bond'

LOGICAL :: test0 = .TRUE.LOGICAL :: test1 = .FALSE.

! How to define constants? After declaration it can not be changedREAL, PARAMETER :: pi=3.14159

Precision

• The precision of a variable may be declared using the KIND-statement

1) SELECTED_INT_KIND(r)2) SELECTED_REAL_KIND(p)3) SELECTED_REAL_KIND(p,r)

Explanations:1) integer, range between -10r < n < 10r 2) real, precision at least p decimals3) real, range -10r < x < 10r and precision at least p decimals

INTEGER, PARAMETER :: short=SELECTED_INT_KIND(4)INTEGER, PARAMETER :: double=SELECTED_REAL_KIND(12,100)INTEGER (KIND=short) :: indexREAL (KIND=double) :: x,y,zCOMPLEX (KIND=double) :: c

x=1.0_double; y=2.0_double * ACOS(x)

OperatorsArithmetic operatorsREAL :: x,yINTEGER :: i = 10x=2.0**(-i) !exponentiation and negation precedence: firstx=x*REAL(i) !multiplication and type change precedence: secondx=x/2.0 !division precedence: secondi=i+1 !addition precedence: thirdi=i-1 !subtraction precedence: third

Relational operators .LT. or < !less than.LE. or <= !less than or equal to.EQ. or == !equal to.NE. or /= !not equal to.GT. or > !greater than.GE. or >= !greater than or equal to

Logical operators.NOT. !logical negation precedence: first.AND. !logical conjunction precedence: second.OR. !logical inclusive disjunction precedence: third.EQV. !logical equivalence precedence: fourth.NEQV. !logical nonequivalence precedence: fourth

L1 L2 .AND. .OR. .EQV. .NEQV.

F F F F T F

F T F T F T

T F F T F T

T T T T T F

LOGICAL :: L1, L2! How to determine the values of logical expressions! F means .FALSE. T means .TRUE.

Logical operators

Control structures1) IF THEN ELSE (branching)2) SELECT CASE (selecting) 3) DO (looping) PROGRAM test_ifIMPLICIT NONEREAL :: x,y,eps,t

WRITE(*,*)' Give x and y :'READ(*,*)x, yeps = EPSILON(x)

IF (ABS(x) > eps) THEN t=y/xELSE WRITE(*,*)'division by zero' t=0.0END IFWRITE(*,*)' y/x = ',tEND PROGRAM

Control structures: IF, ELSE, ELSE IF

PROGRAM test_if

IMPLICIT NONEREAL :: x,y,eps,t

WRITE(*,*)' Give x and y :'READ(*,*)x, yeps = EPSILON(x) IF (ABS(x) > eps) THEN IF (y > eps) THEN t=y/x ELSE IF (ABS(y) < eps) THEN t = 0.0 ELSE t = 1.0 END IFEND IF

END PROGRAM

Control structures: SELECT CASE-SELECT CASE statements matches the entries of a list against the case index. Only one found match is allowed.-Usually arguments are character strings or integers.-DEFAULT-branch if no match found. -If there is no CASE DEFAULT and no match found then the statement following END SELECT is executed... INTEGER :: iLOGICAL :: isprimenumber...SELECT CASE (i) CASE (2,3,5,7) ! variables are not allowed on the list isprimenumber = .TRUE. CASE (1,4,6,8:10) ! case value range, form low:high isprimenumber = .FALSE. CASE DEFAULT ! DEFAULT-branch isprimenumber = testprinumber(i) ! function callEND SELECT...

Control structures: DO, DO WHILE1) DO-loop with an integer counter (count controlled)

INTEGER :: i, stepsize, NumberOfPointsINTEGER, PARAMETER :: max_points=100000REAL :: x_coodinate(max_points), x, totalsum...stepsize=2DO i = 1, NumberOfPoints, stepsize x_coordinate(i) = i*stepsize*0.05END DO

2) DO WHILE-construct (condition controlled loop)

totalsum = 0.0READ(*,*) xDO WHILE (x > 0) totalsum = totalsum + x; READ(*,*) xEND DO

Control structures: DO, DO WHILE3) DO-loop without loop control

REAL :: x, totalsum, epstotalsum = 0.0DO READ(*,*) x IF (x < 0) THEN EXIT ! inside loop control, exit the loop END IF totalsum = totalsum + xEND DO

4) DO-loop, “repeat until” styleeps = 1000.0*EPSILON(1.0)DO ... !Iterative loop body where ABS(x) is getting smaller and smaller IF (ABS(x) < eps) THEN EXIT ! inside loop control, exit the loop END IFEND DO

Control structures: example

PROGRAM gcd! Computes the greatest common divisor, EUCLIDEAN ALGORITHM IMPLICIT NONE INTEGER, PARAMETER :: long = SELECTED_INT_KIND(9) INTEGER (KIND=long) :: m, n, t WRITE(*,*)' Give positive integers m and n :' READ(*,*) m, n WRITE(*,*)'m:', m,' n:', n positivecheck: IF (m > 0 .AND. n > 0) THEN main_algorithm: DO WHILE (n /= 0) t = MOD(m,n) m = n n = t END DO main_algorithm WRITE(*,*)'Greatest common divisor: ',m ELSE WRITE(*,*)'Negative value entered' END IF positivecheck END PROGRAM gcd

Exercise #1

● Create a Fortran program that– reads a real number from a file

– calls a subroutine, which multiplies the value with pi● (subroutine should be in a separate module-file)

– prints the multiplied value to screen

● The whole program is about 15-20 lines