Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

So, what happens next?

Kate Thayer-Calder

CMMAP Grad Student Clqm

July 23, 2008

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

What Happened Before?• Undergraduate degree in Computer Science • Spent 3 years working as a software developer on

pharmaceutical robotic systems• Joined the group knowing basically nothing other

than “I like clouds!”

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

What Happened Next?• The MJO is an important

and poorly understood phenomenon

• Many GCMs are unable to simulate the MJO

• We have two versions of the same model - one produces an MJO and one does not

• GOALS: understand more about the models and more about the MJO

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

Basics of the MJO

• 30 to 70 day Oscillation, aka the intraseasonal oscillation

• Starts in the Indian Ocean and slowly travels eastward (at 4-6 m/s or 9-13 mi/hr)

• Spans 10º-20º of latitude and 50º-100º of longitude– Zonal wavenumbers 1-4

• Generally equatorially trapped, but can move northward or southward in certain cases.

• More commonly appears in boreal winter

Lin et al. 2006

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

Basics of the MJO

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

Current MJO Status

• EOF analysis used at BMRC to determine the current phase of the MJO• Forecasts done using a statistical model instead of traditional model

MJO

You Are Here

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

The Problem

• The MJO is well observed, but not necessarily well understood

• Many models have difficulty simulating the MJO– Only 2 of 14 IPCC AR4 models

came close to having realistic MJO variability

– Study suggests that the convective parameterizations in the models are the source of the differences

• It is difficult to accurately simulate the MJO if we do not understand it!

Lin et al. 2006

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

CAM Deep Convection• Triggered by instability,

clouds persist until CAPE is mostly depleted

• All detrainment occurs at cloud top, which must be above minimum of saturated MSE

• All downdrafts exit below cloud base, and all clouds in the ensemble have the same base

Zhang and McFarlane (1995)

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*

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Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

SP-CAM Clouds and Convection• A 2-D Cloud Resolving Model is

embedded in each GCM gridcell.• Clouds are explicitly simulated,

allowing for many types, heights, and sizes of clouds.

• Nudging from the LS values keeps the CRMs from drifting.

• Results are returned to the LS as sub-grid scale tendencies due to clouds and radiation.

• Currently, momentum is not fedback to the LS, and only the LS surface parameterizations are used.

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

Moistening Through Many Levels

96%

84%

96%

60%

82%

80%

>70%

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

Discharge-Recharge Oscillation

• Proposes MJO is an intrinsic oscillatory state of the tropics• During suppressed convection regimes, shallow clouds moisten and

destabilize the area• Extra-tropical stochastic forcing sets off large-scale convection• Huge convective systems travel through the tropics restabilizing the area and

suppressing convection after their passage.

From Bladé and Hartman 1993

Figure from Benedictand Randall 2007

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

Discharge-Recharge Oscillation

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

Moistening Through Many Levels• CRM in the SP-CAM does

a better job of increasing relative humidity through the column, and loading the lowest levels with vapor

• Heaviest rain occurs in a column with very high relative humidity, downdrafts are not as effective here

• The CAM is much dryer through all layers

75%

65%

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

Cycle of the MJO

• Basic shape of SP-CAM, TC and ERA-40 are all very similar, well correlated precipitation and moistening keeps the cycle running

• Disconnect between precipitation and increasing moisture breaks the Discharge-Recharge Oscillation in the CAM

Rainrate (mm/hr) Rainrate (mm/hr) Rainrate (mm/hr)

TP

W (

kg/m

2 )

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

What’s Happening Now?

• Defended my thesis last spring

• Accepted into the Phd program

• Taught a class on global climate change to undergraduates at Colorado College

• Working on the paper from my thesis

• Have to take the Prelims

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

What Happens Next?

• I have to decide exactly what I’m going to propose for my Phd dissertation– Will probably continue working with tropical

dynamics– Will continue working with models, would

like to add in some new observational toys – Would like to add an aspect of studying

climate change to my research as well– Hope to continue to like clouds

Katherine Thayer-Calder | Grad Student Colloquium | July 23, 2008

Questions?