A SAMPLING OF ISENTROPE ALTITUDE CROSS-SECTIONS
USING THE MICROWAVE TEMPERATURE PROFILER

Bruce L. Gary

2001.12.31

Abbreviations

    IAC = isentrope altitude cross-section (all altitudes are pressure altitude)
    DC951211 = coded way to refer to DC-8 data for flight of 1995 December 11
    MTP = Microwave Temperature Profiler (MTP/DC8 is the 3-channel DC-8 unit, MTP/ER2 is the 2-channel ER-2 unit)
    CAT clear air turbulence

    CA = California (Moffett Field)
    AK = Alaska
    HI = Hawaii (Barber's Point, Oahu)
    ICE = Iceland
    KS = Kansas
    Az = Azores

Introduction

This web page is meant to be a resource for Dr. Liwen Laura Pan, who is studying the atmospheric transition between the tropics and mid-latitudes.

My objective is to present graphical presentations of isentrope altitude cross-sections, IACs, derived from remote temperature profile data taken by JPL's Microwave Temperature Profiler, MTP, on its many flights in the subtropics and elsewhere (for comparison).  Two MTP instruments have so far produced such data, the MTP/ER2 and the MTP/DC8.  On some occasions the MTP/ER2 instrument has been flown on aircraft other than the ER-2, such as the WB57 (I shall refer to such data as being produced by the MTP/B57).  Similarly, the MTP/DC8 instrument has on occasion flown on other aircraft, such as the NCAR L-188C Electra (producing MTP/188 data).  I will begin my survey of subtropical crossing data with MTP/DC8 missions, followed by MTP/ER2 missions.

Flight tracks will be presented for flight over land.  Isentrope altitude cross-sections, IACs, will either be plotted versus time, in kiloseconds (ks), or latitude.  (Sometimes a color-coded IAC will be included; their creation is labor intensive, so only a few are given).  On occasion (when the graphs already exist) I will also include additional supporting data (double tropopause versus latitude, tracer plots, wind plots) that may be useful in data interpreatation.

In viewing the tropopause altitude data recall that the MTP is 1) always right in specifying whether the tropopuase is above versus below flight level, 2) quite accurate in determining the altitude of the tropopause when it is close to flight level (i.e., within 2 km), and 3) not accurate in determining tropopause altitude when it is far from flight level.  In other words, the MTP tropopause is qualitatively reliable, and quantitatively reliable only when the tropopause is nearby.

The following flight data are grouped in two sections:  DC-8 data and ER-2 data.  Additional supporting data is available (BruceLGary@home.com).

List of Flights on This Web Page

    DC1995.12.08    CA/AK
    DC1995.12.11    AK/HI
    DC1995.12.22    HI/CA
    DC1996.02.01    AK/ICE
    DC1996.02.04    ICE/AK
    DC1996.02.08   AK/HI
    DC1996.02.19    HI/CA
    DC1996.05.10    KS/CA
    DC1997.10.29    CI/south/CI

    ER1997.04.22    CA/South/CA
    ER1997.04.24    CA/AK
    ER1997.05.15    AK/CA
    ER1997.06.23    CA/AK
    ER1997.07.12    AK/CA
    ER1997.09.21    AK/HI
    ER1997.09.25    HI/CA

MTP/DC8 Examples

DC 1995.12.08 ......................................................................................................................................

This is a transit flight from CA to AK, and must have flown by the subpolar jet.

Flight track with kilosecond tics labelled.  Green boxes are RAOB sites.

IAC for DC951208, showing tropopause disruption at about 20.5 to 21.0 ks.
 

DC 1995.12.11 ......................................................................................................................................

This flight is from Alaska to Hawaii, and crosses both the subpolar and subtropical jets.

Flight track of southward DC951211 flight.  After passing a polar jet the MTP showed a tropopause altitude jump and an asociated N2O and other tracers (ozone, CO2 and CH4) change (indicative of going from tropospheric to stratospehric air).  A mere 2.5 degrees later all tracers signaled a return to the troposphere.  At 49 degrees latitude, while flying at a constant altitude, we penetrated into stratospheric air (caused by a lowering tropopause).  Mid-flight, at 42 degrees latitude, a second tropopause appeared at a higher altitude and double tropopauses persisted for ~4 degrees of latitude.  After the lower altitude tropopause disappeared the DC-8 encountered a wind maximum, corresponding to the subtropical jet.  This was followed by moderate clear air turbulence, CAT.

IAC for DC951211, plotted versus latitude (times progresses leftward).  Solid black trace is DC-8 altitude. Isentropes are 10 K apart (at 43 North, at 8 km, theta = 310 K).

Color-coded air temperature derived from the MTP/DC8 instrument during the 1995 December 11 DC-8 flight from Alaska to Hawaii.  The arrows are subjective interpretations of a residual circulation that would produce the temperature patern measured by the MTP.  The "J" at 34.5 degrees latitude represents the sub-tropical jet.  White dots show MTP-measured tropopause altitudes.  The heavy dashed line is the "tracer tropopause" and is based on ozone and other tracers, described elsewhere.

This particularly good example of a subtropical jet crossing is described in more detail at http://members.home.net/bgary.mtp2/dc951211/index.html

DC 1995.12.22  ......................................................................................................................................

This is a flight from Hawaii to California.

Flight track with the first two kilosecond ticks labelled.  The subtropical jet is at 23.3 ks.

IAC for this flight.  There is a double tropopause from 24.5 to 30.8 ks, which is on the midlatitude side f the subtropical jet (at 23.3 ks).  Notice that the isentrope above flight level is steepest at the jet.  (Disregard the date error in this figure.)
 

DC 1996.01.24  ......................................................................................................................................

The following flight must have crossed the subpolar jet.

Flight track for DC960124, CA to AK.  Kilosecond ticks are labelled.

IAC for DC960124.

DC 1996.02.01  ......................................................................................................................................

This is an Arctic Winter flight, from Alaska to Iceland.

Flight track, with ks labels, for DC960201, from Alaska to Iceland.

IAC.  Maximum PV was predicted to be at about the 22 to 23 ks location.
 

DC 1996.02.04  ......................................................................................................................................

Here's the return flight, from Iceland to Alaska.

Flight track for DC960204, Iceland to AK.  Kilosecond ticks are labelled.

IAC, showing tropopause jumps 36 and 40 ks.  At 35 to 36 ks the MTP tropopause was at 18 km (not shown), which sometimes happens when flying inside the polar vortex.  In this situation the WMO definition for a tropopause, based as it is upon the temperature profile, is totally misleading.
 

DC 1996.02.08  ......................................................................................................................................

This flight is similar to the previous one, as it goes from Alaska to Hawaii.

Flight track with a summary of events en route.  Again, both the subpolar and subtropical jets were crossed, and MTP-measured tropopauses behaved in correlated ways.  Tracers confirmed tropopause crossings.

IAC versus time.  Double tropopauses exist from 53.5 to 56.3 ks.

IAC versus latitude.  The double tropopause extends from 32 to 39 degrees latitude.

Zoom of he IAC versus time fgiure, showing details of the altitude changes of the lower tropopause.

An additional zoom factor, showing the relationship between CAT and tropopause behavior.  At 54.2 ks moderate CAT was encountered, which coincides with an uplift of the lower tropopause.  This uplift may have been produced by the CAT (that produced adiabatic cooling throughout the turbulently mixed altitude region).

A detailed investigation of this flight is at DC960208.  The focus of this web page is an investigation of evidence for the theory that vertical compression precedes (triggers) CAT.
 

DC 1996.02.19  ......................................................................................................................................

This flight parallels the subtropical jet, then goes north of it, and finally approaches before landing.

Flight track for DC960219.  Ticks are every 2 kiloseconds (ks), starting at 18 ks.  Green squares are RAOB sites.

IAC for DC960219.  Isentropes are 5 K apart.  Tropopause altitdues are shown by small blue triangles.  There actually were two tropopauses for most of this flight, but in this graph only the lower one is shown.  The following 3 figures show both tropopauses.

Double tropopause altitudes versus time for DC960219.

Double tropopause theta versus time for DC960219.

Double tropopause theta versus latitude for DC960219.

N2O versus time for DC960219.  N2O switches from tropospheric values to stratospheric values at 18.5 ks, which corresponds to the time MTP began to detect double tropopauses.  The same pattern exists for CH4, CO and CO2 (plots available upon request; tracer/tracer scatter plots are also available).

DC 1996.05.10  ......................................................................................................................................

This May 1996 flight is from Kansas to California, at the end of the SUCCESS mission.

IAC (versus time).  The tracer tropopause was at theta = 333.5 K (which the DC-8 crossed at 48.2 ks).

There was a double tropopause from the beginning of the flight to 48 ks, and when the upper tropopause (at 16 km) disappeared the lower tropopause rose abruptly from 11.0 to 12 .0 km and slowly rose to 12.6 km by the end of the flight.

This flight exhibits what I have termed a "jumping tropopause" because the lower tropopause abruptly jumps back and forth between two nearby altitudes (11.0 and 11.5 km).  This flight is described in greater detail at DC960510 .

DC 1997.10.29  ......................................................................................................................................

On October 29, 1997, the DC-8 flew a SONWEX Mission local south survey flight from the Azores.  It is said that this flight flew through a "cut-off low" pressure field feature.

Ground track for DC971027.  Kilosecond ticks are shown for only the outbound (southward) portion of flight.

IAC for DC971029.  Tropopause symbols are shown.  The steep isentrope slope at 62.7 ks is associated with a tropopause jump from 13.1 to 14.7 km. Since this was observed during level flight, with no altitude changes, it is very likely "real."  Additional support for the reality of this tropopause jump comes from the fact that the same tropopause behavior is seen at 43.9 ks, when the DC-8 was flying through the same region (in the opposite direction).

A more detailed analysis of this flight data is available at DC971029.
 

MTP/ER2 Examples

ER-2 MTP data covers a smaller altitude region since the MTP/ER2 instrument has only 2-channels, instead of the 3 in the MTP/DC8.  The MTP/ER2 is an older instrument, and is more difficult to calibrate, so this is an additional factor contributing to a smaller altitude coverage.

ER 1997.04.22  ......................................................................................................................................

This is a flight south and back from ARC.

Note that this IAC is plotted versus latitude instead of time.  Since the flight came back on itself there are two traces for each isentrope.  Both traces are at essentially the same altitude except for the 21 to 22 degrees latitude and 19 to 22 km region.    The tropopause was at 11.7 km during ascent, 14.6 km during the dip and 11.7 km during descent.

ER 1997.04.24  ......................................................................................................................................
 

Flight track for CA to AK flight ER970424.

IAC for CA to AK ER970424 flight.  I don't know why the IACs are distorted at 70.0 to70.3 ks.  The tropopause was at 12.8 km during ascent, 10.0 km during the dip and 10.8 km during descent.

ER 1997.05.15  ......................................................................................................................................

Flight track for AK to CA flight ER970515.

IAC for AK to CA flight ER970515.  The tropopause was at 8.1 km during ascent and 12.0 km during descent.

ER 1997.06.23  ......................................................................................................................................

Flight track for CA to AK flight ER970623.

IAC for CA to AK flight ER970523.  The tropopause was at 13.2 km during ascent and 10.7 km during descent.

ER 1997.07.12  ......................................................................................................................................

Flight track for AK to CA flight ER970712.

IAC for AK to CA flight ER970712.  The tropopause was at 10.6 km during ascent and 12.4 km during descent.

ER 1997.09.21  ......................................................................................................................................

Flight track for the AK to HI ER-2 flight of 1997.09.21.  Kilosecond time ticks are labelled.

IAC for 1997.09.21 flight.  Tropopause crossings are shown by the light purple lines.  The sub-tropical jet must be north of 39 degrees latitude, where an altitude "dip" was performed.  Perhaps it is coincident with the steep isentropes at about 42 degrees latitude.

ER 1997.09.25  ......................................................................................................................................

Flight track for ER-2's 1997.09.25 flight from HI to CA, with kilosecond tics labelled.

IAC for 1997.09.25 flight.  Tropopause crossings are shown by the light purple lines.  The sub-tropical jet must be north of 36 degrees north latitude.  The entire flight was within the stratosphere, and MTP measurements show essentially no slope of the isentrope surfaces.
 
 
 
 

____________________________________________________________________

This site opened:  October 26, 2001 Last Update:  December 31, 2001