Alguna grafica sigue haciendo cosas "extrañas"... por lo pronto, ya estamos por encima de 2007 y 2009...

La temperatura media del ártico a punto para volver por debajo de 0º y muy por debajo de la media de los últimos 40 años.

Cita de: El_Buho en Lunes 26 Julio 2010 01:16:27 AM
La temperatura media del ártico a punto para volver por debajo de 0º y muy por debajo de la media de los últimos 40 años.

Las pequeñas sorpresas que os comuniqué hace ya unos meses para el verano parece que empiezan a salir a la luz de forma tangible. Veremos como va evolucionando todo, pero va por el buen camino.
El Buho ha dado un importante dato sobre la temperatura media del Artico y esto no es nada más que el principio.
                                       Un saludo para todos.

Cita de: El_Buho en Lunes 26 Julio 2010 01:16:27 AM
La temperatura media del ártico a punto para volver por debajo de 0º y muy por debajo de la media de los últimos 40 años.

Aquí hay un Gif animado con la temperatura de todos los años DMI entre 1958 y 2010, los valores actuales parecen los mas bajos de toda la serie en verano.

http://www.warwickhughes.com/agri/arctic52.gif

Interesante entrada en Realclimate sobre este tema, escrita por el jefe del grupo de investigación "Hielo marino en el sistema terrestre" del Max Planck Institute en alemán, y traducida al inglés, por el mismo según parece, para realclimate.

http://www.realclimate.org/index.php/archives/2010/07/an-icy-retreat/

Como muchos ya habreis visto, el NSIDC ha actualizado su apartado de noticias y análisis con una entrada de fecha 20 de julio.
http://nsidc.org/arcticseaicenews/

En ella dan cuenta de la ralentización en el deshielo durante el mes de julio, vinculándola con la transición en los patrones de circulación atmosférica dominantes de uno cercano a la "Dipole Anomaly" y con altas presiones sobre el Ártico en junio, a otro más próximo al patrón NAO/AO+ en julio, con bajas presiones sobre el Ártico.
Como ya habíamos comentado por aquí, este modo de circulación observado en juLio favorece los cielos cubiertos y las temperaturas bajas en el Ártico Central, además de tender a dispersar el hielo, aumentando la extensión ocupada por la banquisa.

En esa línea se enmarcan las temperaturas por debajo de la media y próximas a los 0º que registra la gráfica danesa que citabais algunos mensajes más arriba para la banda latitudinal 80-90ºN .
También en esa línea, en las imágenes de las webcams se han podido observar recongelaciones temporales de las "piscinas" de deshielo superficial.

Aún queda verano, y habrá que seguir observando como evolucionan las condiciones.

Saludos.

Se gunda ronda de previsiones de expertos para el mínimo de este verano (valor mensual de septiembre):

"The July Outlook for arctic sea ice extent in September 2010 shows some notable adjustments from the June Outlook, with both downward and upward revisions from last month.

Downward revisions reflect in part rapid ice loss observed during June together with the presence of the Arctic Dipole Anomaly (DA), which promotes clear skies, warm air temperatures, and winds that push ice away from coastal areas and encourages melt. Upward revisions reflect the slowdown of ice loss during the first two weeks of July and a change in atmospheric conditions to cooler, cloudier weather."



http://www.arcus.org/search/seaiceoutlook/2010/july

Veo que el inefable Wilson se mantiene fuerte en su postura de un milloncejo de kms2...

Wilson en sus trece.


Algunos titulares:
Los modelos discrepan. Mientras nuestro viejo conocido PIOMAS pilotado por Zhang insiste en un valor bajo, de 4.7 ó 4.8 millones de km2., los modelos de Kauker et al. y McLaren et al., en cambio, pronostican un mínimo parecido al del año pasado, en torno a 5.5 millones de km2. En parte se basan en la presencia de sólido hielo multianual en el mar de Siberia Oriental. Hay observaciones de campo confirmando su presencia. Aunque ojo, porque con bajas presiones dominando el Ártico esta zona es la más expuesta a las invasiones de aire cálido.

"Of interest is that the PIOMAS (Pan-Arctic Ice-Ocean Modeling and Assimilation System) model continues to indicate that the ice is very thin, leading Lindsay and Zhang to predict a new record low for September 2010 with an R2 value of 0.84, suggesting a high degree of skill in the forecast. The numerical modeling methods of Kauker et al. and McLaren et al., however, predict a return to September 2009 conditions, based in part on the presence of older and thicker ice in the East Siberian Sea."
"Field observations summarized in the contribution by Hutchings and discussed in this month's Regional Outlook  indicate that starting ice thicknesses were comparable to last year in the Beaufort and Chukchi Seas, and that after getting off to a fast start, melt has slowed down considerably, resulting in below-normal melt rates. Buoys show this ice moving into the East Siberian Sea, lending some support to the notion of thicker, more enduring ice in this region.

A lot will depend on the persistence of the low pressure over the central Arctic Ocean. Ice divergence has spread the ice out, slowing the decline in sea ice extent during the first two weeks of July. Yet at the same time, this ice divergence is starting to create openings in the ice pack that readily absorb solar energy, which can lead to more melt. If the ice is as thin as the PIOMAS model suggests, the rate of ice loss is likely to speed up considerably in the next couple of weeks"

"Although ice extent at the end of June 2010 was slightly lower than that observed in 2007 (Figure 2), the persistence of the Arctic Dipole Anomaly (DA) throughout the summer of 2007 resulted in an acceleration of ice loss in July that led to the record low ice extent in September 2007. In May and June 2010, the DA was present again, helping to speed up ice loss by promoting clear skies, advection of warm air into the Arctic, and strong offshore winds that move ice away from the coasts. However, in July the sea level pressure (SLP) pattern shifted back to a more typical low pressure region over the central Arctic Ocean (Figure 3), causing ice divergence that has significantly slowed ice loss during the first two weeks of July (Figure 2). This shift is an early repeat of last year."

Presión media a nivel del mar del 1 al 19 de julio:


"From July 1-July 20, the rate of ice loss averaged -79,810 square kilometers per day. This is a decrease from the average rate of ice loss for June 2010 of -85,210 square kilometers per day, and is slower than climatology (average of -84,050 square kilometers per day for 1979-2000)."

Edad estimada del hielo, 21 de junio de 2010:




Y otra cosa: sigue la unanimidad en el que el Paso del Noroeste no se abrirá este año.
Veremos. Aspecto hace un par de días:

DMI contra GISS: diferencias de metodo.

---

Aunque podría ir también en el apartado de temperatura global sobre todo por la incidencia de dicha zona en el dato de anomalías de temperaturas global de GISS Temperature Paper lo pondré aquí.



GISS Arctic vs DMI Arctic: differences in method




Dear DMI:

I am an American journalist completing a book about climate change and have been studying your Arctic temperature graph for some time. The graph says that the data are obtained by the use of a model.

I wonder if you can tell me how many temperature stations the average represents, and why the word model is used. (I would anticipate the word "model" to be a predictive computer analysis, as opposed to descriptive.)

Would it be possible to clear this up?

Thank you in advance.

Sincerely yours,

Harold Ambler





To which Dybkjær responded:

Dear Harold

Concerning your question about the number of in situ temperature observations (direct measurements) there is available in the Arctic – the brief answer is – there are not many! My guess is that the number of buoys in the Arctic Ocean that provide near-real-time temperature observations for e.g. numerical weather prediction (NWP) models are around 50. The number of land based weather stations on the rim of the Arctic Ocean are probably even less. You must contact WMO (world meteorological organization) for more accurate numbers.  So by dividing the area that the 'mean temperature' graph represents by 100 temperature observations, you will of course find that each observation must represent an enormous area. That is exactly why you want to use NWP models to estimate distributed temperatures in the Arctic.

The NWP models used for the 'mean plus 80N temperature'-graph on ocean.dmi.dk are, as you mention, a predictive numerical model. However, before you let the model 'go' to do the weather forecast calculations, you must estimate the initial state of the atmosphere. The initial state of the atmosphere is the best guess, based of all observation you have available and the coupled physical constrains of the model. The approximately 100 in situ surface temperature observations is only a very limited part of 'all available observations' you feed into the model. You have measurements from airplanes, atmospheric profiling instruments mounted on balloons and then of course the far most valuable input to NWP models today – a huge amount of observations from satellite.

From these data sources all kinds of atmospheric variables are measured/estimated and assimilated into the NWP models. From a 'bargain' between the coupled model physics and all the applied observations the model calculates the best initial state of the entire atmosphere. That initial state – the model analysis – is the best guess of e.g. distributed surface temperatures in the Arctic you get.

Hope you can use this clarification.

Best Regards

Gorm /Center for Ocean and Ice, DMI

I found Dybkjær's response helpful and also confusing. Below are follow-up questions I sent him paired with his responses:



Hi Gorm,

Thank you for your response.

I think I am understanding you somewhat and have a few follow-up questions:





1. Does DMI's 'mean plus 80N temperature'-graph use measurements from airplanes?


All available observations, including measurements from airplanes, are used by the models to calculate the best guess of the atmospheric condition. This 'best guess' (or 'analysis') is calculated 4 times per day of which the 00z and 12z are the basis for the 'plus 80North' temperature graph. I must recommend you to contact "European Centre for Medium-Range Weather Forecasts" (ecmwf.int) for details on the amount of observation they use for any of their model analysis.


2. Do you use measurements from satelllites?

Dybkjær: A huge amount of satellite data are also used to produce the 'best guess'... (see above)

3. Do you use measurements from balloons?

see above

4. Does the number of data-sources change on a daily basis?

Yes – but I do not believe this has a significant effect on the day to day quality. Contact the ECMWF!

5. Do you adjust for this?

No

6. If you do use the sources listed in 1-3, who provides you with the data?

At DMI we get most of our ground based measurements through the WMO – satellite data we either retrieve our selves or get them through various data networks. I guess the same is the case at ECMWF, who run the models used for the temperature graph we are talking about here – so for more details on this please contact ECMWF.

7. Some of the spikes in the record look extraordinarily sharp, and I had previously understood such moments to be cases where sub-polar air overran the Arctic basin. But I wonder if, to some extent, they represent the model over-reacting to a single spike in data from just a few sources? For instance, when I eyeball the temperatures around the Arctic basin, they don't in every case appear to correspond to the spikes on your graph?

I believe – in general terms – that the spikes of the graph are realistic, but to discuss this further we have to look at specific cases. As I mentioned in an earlier mail, the 'plus 80 North mean temperature'-values are the mean of all model grid points in a regular 0.5 degree grid – meaning that along each half degree parallel North of 82N, you have 720 temperature values! That means that the 'plus 80 North mean temperature' is strongly bias towards the temperatures in the very central arctic and therefore less affected by temperatures along the rim of the Arctic Ocean. Therefore – You can use all the plotted 'plus 80 North mean temperature' graphs to compare one year to another or the climate line and you should NOT compare the mean temperatures to a specific temperature measurement.

8. The word model is still confounding here: Basically, the graph represents initial conditions for you to run the model predictions. But the initial conditions are not generated by the model. They are generated by you and the staff at DMI, correct?

The initial conditions are generated by the model using state-of-the-art atmosphere physical knowledge.

Pues vamos bien, las extrapolaciones del GISS a 1200 km le meten 4 grados mínimo de anomalia al polo, y las mediciones en la zona del gráfico que encontré sobre temperaturas por encima de los 80ºN lo meten por debajo de la media de los últimos 40 años.
Creo que este tema debería estar en seguimiento de la temperatura global.

Este año, según las imágenes de las webcams el deshielo superficial se ha iniciado entre el 20 y el 25 de junio, tras algunos amagos anteriores. Aquí tenemos una imagen de la segunda webcam el día 26 de junio, en la que se observa ya claramente deshielo en la superficie:


En pocos días el deshielo progresó formándose las típicas "piscinas" que observamos en esta imagen del 7 de julio:


No obstante, ya desde esa primera semana de julio el deshielo se ralentizó mucho, alternándose días de parcial recongelación con otros en los que vuelven a observarse las "piscinas". (Esto se ha debido al cambio de patrón de circulación atmosférica al que ya nos hemos referido anteriormente por aquí, con bajas presiones sobre la zona de las webcams, cielos cubiertos, precipitaciones de nieve y temperaturas relativamente bajas para la fecha.)
En esta imagen del día 23 de julio podemos ver la superficie recongelada e incluso cubierta de nieve:


Durante los días de esta última imagen, la estación situada junto a la webcam registraba unos -2ºC (ver aquí)

En los últimos días, continúan los altibajos, las temperaturas han subido hasta los 0ºC, y esta es la última imagen disponible, de ayer 29 de julio. La "piscina" vuelve a ser observable:


Por otro lado, es interesante el mapa mostrando la deriva de la webcam desde su instalación en abril. Ver la línea roja:


Lo más habitual en los últimos años era que las placas de hielo sobre las que se sitúan las webcams fueran atrapadas por la Deriva Transpolar para terminar expulsadas a finales de verano por el estrecho de Fram.
Este año no parece que tal cosa vaya a suceder.
Su desplazamiento en los tres primeros meses ha sido relativamente lento, en consonancia con una Deriva Transpolar debilitada. Durante el último mes, han cambiado de dirección en su deriva, reflejando la transición de circulación anticiclónica a ciclónica ocurrida en julio.

Deshielo superficial de la banquisa ártica en 2010 visto por las webcams